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Junio C Hamano	dca3482	2010-02-13 01:02:52	[diff] [blame]	1	<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User's Manual (for version 1.5.3 or newer)</title><link rel="stylesheet" href="docbook-xsl.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book" title="Git User's Manual (for version 1.5.3 or newer)"><div class="titlepage"><div><div><h1 class="title"><a name="id332960"></a>Git User's Manual (for version 1.5.3 or newer)</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="preface"><a href="#id332970">Preface</a></span></dt><dt><span class="chapter"><a href="#repositories-and-branches">1. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#exploring-git-history">2. Exploring git history</a></span></dt><dd><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-comments-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#Developing-With-git">3. Developing with git</a></span></dt><dd><dl><dt><span class="section"><a href="#telling-git-your-name">Telling git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#sharing-development">4. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a git repository via the git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via http</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">5. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#advanced-branch-management">6. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#git-concepts">7. Git concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></dd><dt><span class="chapter"><a href="#submodules">8. Submodules</a></span></dt><dd><dl><dt><span class="section"><a href="#_pitfalls_with_submodules">Pitfalls with submodules</a></span></dt></dl></dd><dt><span class="chapter"><a href="#low-level-operations">9. Low-level git operations</a></span></dt><dd><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory -> index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index -> object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database -> index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index -> working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hacking-git">10. Hacking git</a></span></dt><dd><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git's source code</a></span></dt></dl></dd><dt><span class="chapter"><a href="#glossary">11. Git Glossary</a></span></dt><dt><span class="appendix"><a href="#git-quick-start">A. Git Quick Reference</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></dd><dt><span class="appendix"><a href="#todo">B. Notes and todo list for this manual</a></span></dt></dl></div><div class="preface" title="Preface"><div class="titlepage"><div><div><h2 class="title"><a name="id332970"></a>Preface</h2></div></div></div><p>Git is a fast distributed revision control system.</p><p>This manual is designed to be readable by someone with basic UNIX
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2	command-line skills, but no previous knowledge of git.</p><p><a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a> and <a class="xref" href="#exploring-git-history" title="Chapter 2. Exploring git history">Chapter 2, <i>Exploring git history</i></a> explain how
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	3	to fetch and study a project using git—read these chapters to learn how
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	4	to build and test a particular version of a software project, search for
				5	regressions, and so on.</p><p>People needing to do actual development will also want to read
Junio C Hamano	ec87f52	2008-12-10 08:35:25	[diff] [blame]	6	<a class="xref" href="#Developing-With-git" title="Chapter 3. Developing with git">Chapter 3, <i>Developing with git</i></a> and <a class="xref" href="#sharing-development" title="Chapter 4. Sharing development with others">Chapter 4, <i>Sharing development with others</i></a>.</p><p>Further chapters cover more specialized topics.</p><p>Comprehensive reference documentation is available through the man
Junio C Hamano	f66ecee	2008-11-17 18:25:43	[diff] [blame]	7	pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command
				8	"git clone <repo>", you can either use:</p><div class="literallayout"><p>$ man git-clone</p></div><p>or:</p><div class="literallayout"><p>$ git help clone</p></div><p>With the latter, you can use the manual viewer of your choice; see
				9	<a class="ulink" href="git-help.html" target="_top">git-help(1)</a> for more information.</p><p>See also <a class="xref" href="#git-quick-start" title="Appendix A. Git Quick Reference">Appendix A, <i>Git Quick Reference</i></a> for a brief overview of git commands,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	10	without any explanation.</p><p>Finally, see <a class="xref" href="#todo" title="Appendix B. Notes and todo list for this manual">Appendix B, <i>Notes and todo list for this manual</i></a> for ways that you can help make this manual more
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	11	complete.</p></div><div class="chapter" title="Chapter 1. Repositories and Branches"><div class="titlepage"><div><div><h2 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></div><div class="section" title="How to get a git repository"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository"></a>How to get a git repository</h2></div></div></div><p>It will be useful to have a git repository to experiment with as you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	12	read this manual.</p><p>The best way to get one is by using the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> command to
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	13	download a copy of an existing repository. If you don't already have a
				14	project in mind, here are some interesting examples:</p><div class="literallayout"><p> # git itself (approx. 10MB download):<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	15	$ git clone git://git.kernel.org/pub/scm/git/git.git<br>
Junio C Hamano	4fbdd44	2009-01-06 05:56:24	[diff] [blame]	16	# the Linux kernel (approx. 150MB download):<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	17	$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git</p></div><p>The initial clone may be time-consuming for a large project, but you
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	18	will only need to clone once.</p><p>The clone command creates a new directory named after the project ("git"
				19	or "linux-2.6" in the examples above). After you cd into this
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	20	directory, you will see that it contains a copy of the project files,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	21	called the <a class="link" href="#def_working_tree">working tree</a>, together with a special
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	22	top-level directory named ".git", which contains all the information
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	23	about the history of the project.</p></div><div class="section" title="How to check out a different version of a project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-check-out"></a>How to check out a different version of a project</h2></div></div></div><p>Git is best thought of as a tool for storing the history of a collection
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	24	of files. It stores the history as a compressed collection of
				25	interrelated snapshots of the project's contents. In git each such
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	26	version is called a <a class="link" href="#def_commit">commit</a>.</p><p>Those snapshots aren't necessarily all arranged in a single line from
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	27	oldest to newest; instead, work may simultaneously proceed along
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	28	parallel lines of development, called <a class="link" href="#def_branch">branches</a>, which may
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	29	merge and diverge.</p><p>A single git repository can track development on multiple branches. It
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	30	does this by keeping a list of <a class="link" href="#def_head">heads</a> which reference the
				31	latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	32	you the list of branch heads:</p><div class="literallayout"><p>$ git branch<br>
				33	* master</p></div><p>A freshly cloned repository contains a single branch head, by default
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	34	named "master", with the working directory initialized to the state of
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	35	the project referred to by that branch head.</p><p>Most projects also use <a class="link" href="#def_tag">tags</a>. Tags, like heads, are
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	36	references into the project's history, and can be listed using the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	37	<a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command:</p><div class="literallayout"><p>$ git tag -l<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	38	v2.6.11<br>
				39	v2.6.11-tree<br>
				40	v2.6.12<br>
				41	v2.6.12-rc2<br>
				42	v2.6.12-rc3<br>
				43	v2.6.12-rc4<br>
				44	v2.6.12-rc5<br>
				45	v2.6.12-rc6<br>
				46	v2.6.13<br>
				47	...</p></div><p>Tags are expected to always point at the same version of a project,
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	48	while heads are expected to advance as development progresses.</p><p>Create a new branch head pointing to one of these versions and check it
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	49	out using <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>:</p><div class="literallayout"><p>$ git checkout -b new v2.6.13</p></div><p>The working directory then reflects the contents that the project had
				50	when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	51	branches, with an asterisk marking the currently checked-out branch:</p><div class="literallayout"><p>$ git branch<br>
				52	master<br>
				53	* new</p></div><p>If you decide that you'd rather see version 2.6.17, you can modify
				54	the current branch to point at v2.6.17 instead, with</p><div class="literallayout"><p>$ git reset --hard v2.6.17</p></div><p>Note that if the current branch head was your only reference to a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	55	particular point in history, then resetting that branch may leave you
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	56	with no way to find the history it used to point to; so use this command
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	57	carefully.</p></div><div class="section" title="Understanding History: Commits"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="understanding-commits"></a>Understanding History: Commits</h2></div></div></div><p>Every change in the history of a project is represented by a commit.
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	58	The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	59	current branch:</p><div class="literallayout"><p>$ git show<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	60	commit 17cf781661e6d38f737f15f53ab552f1e95960d7<br>
				61	Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)><br>
				62	Date: Tue Apr 19 14:11:06 2005 -0700<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	63	<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	64	Remove duplicate getenv(DB_ENVIRONMENT) call<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	65	<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	66	Noted by Tony Luck.<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	67	<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	68	diff --git a/init-db.c b/init-db.c<br>
				69	index 65898fa..b002dc6 100644<br>
				70	--- a/init-db.c<br>
				71	+++ b/init-db.c<br>
				72	@@ -7,7 +7,7 @@<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	73	<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	74	int main(int argc, char **argv)<br>
				75	{<br>
				76	- char sha1_dir = getenv(DB_ENVIRONMENT), path;<br>
				77	+ char sha1_dir, path;<br>
				78	int len, i;<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	79	<br>
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	80	if (mkdir(".git", 0755) < 0) {</p></div><p>As you can see, a commit shows who made the latest change, what they
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	81	did, and why.</p><p>Every commit has a 40-hexdigit id, sometimes called the "object name" or the
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	82	"SHA-1 id", shown on the first line of the "git show" output. You can usually
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	83	refer to a commit by a shorter name, such as a tag or a branch name, but this
				84	longer name can also be useful. Most importantly, it is a globally unique
				85	name for this commit: so if you tell somebody else the object name (for
				86	example in email), then you are guaranteed that name will refer to the same
				87	commit in their repository that it does in yours (assuming their repository
				88	has that commit at all). Since the object name is computed as a hash over the
				89	contents of the commit, you are guaranteed that the commit can never change
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	90	without its name also changing.</p><p>In fact, in <a class="xref" href="#git-concepts" title="Chapter 7. Git concepts">Chapter 7, <i>Git concepts</i></a> we shall see that everything stored in git
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	91	history, including file data and directory contents, is stored in an object
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	92	with a name that is a hash of its contents.</p><div class="section" title="Understanding history: commits, parents, and reachability"><div class="titlepage"><div><div><h3 class="title"><a name="understanding-reachability"></a>Understanding history: commits, parents, and reachability</h3></div></div></div><p>Every commit (except the very first commit in a project) also has a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	93	parent commit which shows what happened before this commit.
				94	Following the chain of parents will eventually take you back to the
				95	beginning of the project.</p><p>However, the commits do not form a simple list; git allows lines of
				96	development to diverge and then reconverge, and the point where two
				97	lines of development reconverge is called a "merge". The commit
				98	representing a merge can therefore have more than one parent, with
				99	each parent representing the most recent commit on one of the lines
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	100	of development leading to that point.</p><p>The best way to see how this works is using the <a class="ulink" href="gitk.html" target="_top">gitk(1)</a>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	101	command; running gitk now on a git repository and looking for merge
				102	commits will help understand how the git organizes history.</p><p>In the following, we say that commit X is "reachable" from commit Y
				103	if commit X is an ancestor of commit Y. Equivalently, you could say
Junio C Hamano	a638742	2007-08-25 03:54:27	[diff] [blame]	104	that Y is a descendant of X, or that there is a chain of parents
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	105	leading from commit Y to commit X.</p></div><div class="section" title="Understanding history: History diagrams"><div class="titlepage"><div><div><h3 class="title"><a name="history-diagrams"></a>Understanding history: History diagrams</h3></div></div></div><p>We will sometimes represent git history using diagrams like the one
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	106	below. Commits are shown as "o", and the links between them with
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	107	lines drawn with - / and \. Time goes left to right:</p><pre class="literallayout"> o--o--o <-- Branch A
				108	/
				109	o--o--o <-- master
				110	\
				111	o--o--o <-- Branch B</pre><p>If we need to talk about a particular commit, the character "o" may
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	112	be replaced with another letter or number.</p></div><div class="section" title="Understanding history: What is a branch?"><div class="titlepage"><div><div><h3 class="title"><a name="what-is-a-branch"></a>Understanding history: What is a branch?</h3></div></div></div><p>When we need to be precise, we will use the word "branch" to mean a line
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	113	of development, and "branch head" (or just "head") to mean a reference
				114	to the most recent commit on a branch. In the example above, the branch
				115	head named "A" is a pointer to one particular commit, but we refer to
				116	the line of three commits leading up to that point as all being part of
				117	"branch A".</p><p>However, when no confusion will result, we often just use the term
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	118	"branch" both for branches and for branch heads.</p></div></div><div class="section" title="Manipulating branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manipulating-branches"></a>Manipulating branches</h2></div></div></div><p>Creating, deleting, and modifying branches is quick and easy; here's
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	119	a summary of the commands:</p><div class="variablelist"><dl><dt><span class="term">
				120	git branch
				121	</span></dt><dd>
				122	list all branches
				123	</dd><dt><span class="term">
				124	git branch <branch>
				125	</span></dt><dd>
				126	create a new branch named <branch>, referencing the same
				127	point in history as the current branch
				128	</dd><dt><span class="term">
				129	git branch <branch> <start-point>
				130	</span></dt><dd>
				131	create a new branch named <branch>, referencing
				132	<start-point>, which may be specified any way you like,
				133	including using a branch name or a tag name
				134	</dd><dt><span class="term">
				135	git branch -d <branch>
				136	</span></dt><dd>
				137	delete the branch <branch>; if the branch you are deleting
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	138	points to a commit which is not reachable from the current
				139	branch, this command will fail with a warning.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	140	</dd><dt><span class="term">
				141	git branch -D <branch>
				142	</span></dt><dd>
				143	even if the branch points to a commit not reachable
				144	from the current branch, you may know that that commit
				145	is still reachable from some other branch or tag. In that
				146	case it is safe to use this command to force git to delete
				147	the branch.
				148	</dd><dt><span class="term">
				149	git checkout <branch>
				150	</span></dt><dd>
				151	make the current branch <branch>, updating the working
				152	directory to reflect the version referenced by <branch>
				153	</dd><dt><span class="term">
				154	git checkout -b <new> <start-point>
				155	</span></dt><dd>
				156	create a new branch <new> referencing <start-point>, and
				157	check it out.
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	158	</dd></dl></div><p>The special symbol "HEAD" can always be used to refer to the current
				159	branch. In fact, git uses a file named "HEAD" in the .git directory to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	160	remember which branch is current:</p><div class="literallayout"><p>$ cat .git/HEAD<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	161	ref: refs/heads/master</p></div></div><div class="section" title="Examining an old version without creating a new branch"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="detached-head"></a>Examining an old version without creating a new branch</h2></div></div></div><p>The <code class="literal">git checkout</code> command normally expects a branch head, but will also
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	162	accept an arbitrary commit; for example, you can check out the commit
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	163	referenced by a tag:</p><div class="literallayout"><p>$ git checkout v2.6.17<br>
				164	Note: moving to "v2.6.17" which isn't a local branch<br>
				165	If you want to create a new branch from this checkout, you may do so<br>
				166	(now or later) by using -b with the checkout command again. Example:<br>
				167	git checkout -b <new_branch_name><br>
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	168	HEAD is now at 427abfa... Linux v2.6.17</p></div><p>The HEAD then refers to the SHA-1 of the commit instead of to a branch,
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	169	and git branch shows that you are no longer on a branch:</p><div class="literallayout"><p>$ cat .git/HEAD<br>
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	170	427abfa28afedffadfca9dd8b067eb6d36bac53f<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	171	$ git branch<br>
				172	* (no branch)<br>
				173	master</p></div><p>In this case we say that the HEAD is "detached".</p><p>This is an easy way to check out a particular version without having to
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	174	make up a name for the new branch. You can still create a new branch
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	175	(or tag) for this version later if you decide to.</p></div><div class="section" title="Examining branches from a remote repository"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-remote-branches"></a>Examining branches from a remote repository</h2></div></div></div><p>The "master" branch that was created at the time you cloned is a copy
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	176	of the HEAD in the repository that you cloned from. That repository
				177	may also have had other branches, though, and your local repository
				178	keeps branches which track each of those remote branches, which you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	179	can view using the "-r" option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p><div class="literallayout"><p>$ git branch -r<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	180	origin/HEAD<br>
				181	origin/html<br>
				182	origin/maint<br>
				183	origin/man<br>
				184	origin/master<br>
				185	origin/next<br>
				186	origin/pu<br>
				187	origin/todo</p></div><p>You cannot check out these remote-tracking branches, but you can
				188	examine them on a branch of your own, just as you would a tag:</p><div class="literallayout"><p>$ git checkout -b my-todo-copy origin/todo</p></div><p>Note that the name "origin" is just the name that git uses by default
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	189	to refer to the repository that you cloned from.</p></div><div class="section" title="Naming branches, tags, and other references"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div><p>Branches, remote-tracking branches, and tags are all references to
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	190	commits. All references are named with a slash-separated path name
				191	starting with "refs"; the names we've been using so far are actually
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	192	shorthand:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	193	The branch "test" is short for "refs/heads/test".
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	194	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	195	The tag "v2.6.18" is short for "refs/tags/v2.6.18".
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	196	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	197	"origin/master" is short for "refs/remotes/origin/master".
				198	</li></ul></div><p>The full name is occasionally useful if, for example, there ever
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	199	exists a tag and a branch with the same name.</p><p>(Newly created refs are actually stored in the .git/refs directory,
				200	under the path given by their name. However, for efficiency reasons
				201	they may also be packed together in a single file; see
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	202	<a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>).</p><p>As another useful shortcut, the "HEAD" of a repository can be referred
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	203	to just using the name of that repository. So, for example, "origin"
				204	is usually a shortcut for the HEAD branch in the repository "origin".</p><p>For the complete list of paths which git checks for references, and
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	205	the order it uses to decide which to choose when there are multiple
				206	references with the same shorthand name, see the "SPECIFYING
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	207	REVISIONS" section of <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a>.</p></div><div class="section" title="Updating a repository with git fetch"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-With-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div><p>Eventually the developer cloned from will do additional work in her
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	208	repository, creating new commits and advancing the branches to point
				209	at the new commits.</p><p>The command "git fetch", with no arguments, will update all of the
				210	remote-tracking branches to the latest version found in her
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	211	repository. It will not touch any of your own branches—not even the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	212	"master" branch that was created for you on clone.</p></div><div class="section" title="Fetching branches from other repositories"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-branches"></a>Fetching branches from other repositories</h2></div></div></div><p>You can also track branches from repositories other than the one you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	213	cloned from, using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>:</p><div class="literallayout"><p>$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	214	$ git fetch linux-nfs<br>
				215	* refs/remotes/linux-nfs/master: storing branch 'master' ...<br>
				216	commit: bf81b46</p></div><p>New remote-tracking branches will be stored under the shorthand name
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	217	that you gave "git remote add", in this case linux-nfs:</p><div class="literallayout"><p>$ git branch -r<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	218	linux-nfs/master<br>
				219	origin/master</p></div><p>If you run "git fetch <remote>" later, the tracking branches for the
				220	named <remote> will be updated.</p><p>If you examine the file .git/config, you will see that git has added
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	221	a new stanza:</p><div class="literallayout"><p>$ cat .git/config<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	222	...<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	223	[remote "linux-nfs"]<br>
				224	url = git://linux-nfs.org/pub/nfs-2.6.git<br>
				225	fetch = +refs/heads/:refs/remotes/linux-nfs/<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	226	...</p></div><p>This is what causes git to track the remote's branches; you may modify
				227	or delete these configuration options by editing .git/config with a
				228	text editor. (See the "CONFIGURATION FILE" section of
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	229	<a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.)</p></div></div><div class="chapter" title="Chapter 2. Exploring git history"><div class="titlepage"><div><div><h2 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring git history</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-comments-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></div><p>Git is best thought of as a tool for storing the history of a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	230	collection of files. It does this by storing compressed snapshots of
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	231	the contents of a file hierarchy, together with "commits" which show
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	232	the relationships between these snapshots.</p><p>Git provides extremely flexible and fast tools for exploring the
Junio C Hamano	39381a7	2007-02-02 07:35:15	[diff] [blame]	233	history of a project.</p><p>We start with one specialized tool that is useful for finding the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	234	commit that introduced a bug into a project.</p><div class="section" title="How to use bisect to find a regression"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-bisect"></a>How to use bisect to find a regression</h2></div></div></div><p>Suppose version 2.6.18 of your project worked, but the version at
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	235	"master" crashes. Sometimes the best way to find the cause of such a
				236	regression is to perform a brute-force search through the project's
				237	history to find the particular commit that caused the problem. The
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	238	<a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p><div class="literallayout"><p>$ git bisect start<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	239	$ git bisect good v2.6.18<br>
				240	$ git bisect bad master<br>
				241	Bisecting: 3537 revisions left to test after this<br>
				242	[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</p></div><p>If you run "git branch" at this point, you'll see that git has
Junio C Hamano	9e39507	2008-07-31 22:11:21	[diff] [blame]	243	temporarily moved you in "(no branch)". HEAD is now detached from any
				244	branch and points directly to a commit (with commit id 65934…) that
				245	is reachable from "master" but not from v2.6.18. Compile and test it,
				246	and see whether it crashes. Assume it does crash. Then:</p><div class="literallayout"><p>$ git bisect bad<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	247	Bisecting: 1769 revisions left to test after this<br>
				248	[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</p></div><p>checks out an older version. Continue like this, telling git at each
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	249	stage whether the version it gives you is good or bad, and notice
				250	that the number of revisions left to test is cut approximately in
				251	half each time.</p><p>After about 13 tests (in this case), it will output the commit id of
				252	the guilty commit. You can then examine the commit with
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	253	<a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	254	report with the commit id. Finally, run</p><div class="literallayout"><p>$ git bisect reset</p></div><p>to return you to the branch you were on before.</p><p>Note that the version which <code class="literal">git bisect</code> checks out for you at each
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	255	point is just a suggestion, and you're free to try a different
				256	version if you think it would be a good idea. For example,
				257	occasionally you may land on a commit that broke something unrelated;
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	258	run</p><div class="literallayout"><p>$ git bisect visualize</p></div><p>which will run gitk and label the commit it chose with a marker that
Junio C Hamano	d32738e	2008-07-09 19:53:42	[diff] [blame]	259	says "bisect". Choose a safe-looking commit nearby, note its commit
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	260	id, and check it out with:</p><div class="literallayout"><p>$ git reset --hard fb47ddb2db...</p></div><p>then test, run "bisect good" or "bisect bad" as appropriate, and
Junio C Hamano	9e39507	2008-07-31 22:11:21	[diff] [blame]	261	continue.</p><p>Instead of "git bisect visualize" and then "git reset —hard
				262	fb47ddb2db…", you might just want to tell git that you want to skip
				263	the current commit:</p><div class="literallayout"><p>$ git bisect skip</p></div><p>In this case, though, git may not eventually be able to tell the first
Junio C Hamano	610d176	2008-11-28 06:27:13	[diff] [blame]	264	bad one between some first skipped commits and a later bad commit.</p><p>There are also ways to automate the bisecting process if you have a
Junio C Hamano	9e39507	2008-07-31 22:11:21	[diff] [blame]	265	test script that can tell a good from a bad commit. See
				266	<a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other "git
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	267	bisect" features.</p></div><div class="section" title="Naming commits"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="naming-commits"></a>Naming commits</h2></div></div></div><p>We have seen several ways of naming commits already:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	268	40-hexdigit object name
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	269	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	270	branch name: refers to the commit at the head of the given
				271	branch
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	272	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	273	tag name: refers to the commit pointed to by the given tag
				274	(we've seen branches and tags are special cases of
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	275	<a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>).
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	276	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	277	HEAD: refers to the head of the current branch
				278	</li></ul></div><p>There are many more; see the "SPECIFYING REVISIONS" section of the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	279	<a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> man page for the complete list of ways to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	280	name revisions. Some examples:</p><div class="literallayout"><p>$ git show fb47ddb2 # the first few characters of the object name<br>
				281	# are usually enough to specify it uniquely<br>
				282	$ git show HEAD^ # the parent of the HEAD commit<br>
				283	$ git show HEAD^^ # the grandparent<br>
				284	$ git show HEAD~4 # the great-great-grandparent</p></div><p>Recall that merge commits may have more than one parent; by default,
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	285	^ and ~ follow the first parent listed in the commit, but you can
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	286	also choose:</p><div class="literallayout"><p>$ git show HEAD^1 # show the first parent of HEAD<br>
				287	$ git show HEAD^2 # show the second parent of HEAD</p></div><p>In addition to HEAD, there are several other special names for
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	288	commits:</p><p>Merges (to be discussed later), as well as operations such as
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	289	<code class="literal">git reset</code>, which change the currently checked-out commit, generally
				290	set ORIG_HEAD to the value HEAD had before the current operation.</p><p>The <code class="literal">git fetch</code> operation always stores the head of the last fetched
				291	branch in FETCH_HEAD. For example, if you run <code class="literal">git fetch</code> without
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	292	specifying a local branch as the target of the operation</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git theirbranch</p></div><p>the fetched commits will still be available from FETCH_HEAD.</p><p>When we discuss merges we'll also see the special name MERGE_HEAD,
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	293	which refers to the other branch that we're merging in to the current
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	294	branch.</p><p>The <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	295	occasionally useful for translating some name for a commit to the object
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	296	name for that commit:</p><div class="literallayout"><p>$ git rev-parse origin<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	297	e05db0fd4f31dde7005f075a84f96b360d05984b</p></div></div><div class="section" title="Creating tags"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-tags"></a>Creating tags</h2></div></div></div><p>We can also create a tag to refer to a particular commit; after
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	298	running</p><div class="literallayout"><p>$ git tag stable-1 1b2e1d63ff</p></div><p>You can use stable-1 to refer to the commit 1b2e1d63ff.</p><p>This creates a "lightweight" tag. If you would also like to include a
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	299	comment with the tag, and possibly sign it cryptographically, then you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	300	should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	301	for details.</p></div><div class="section" title="Browsing revisions"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="browsing-revisions"></a>Browsing revisions</h2></div></div></div><p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	302	own, it shows all commits reachable from the parent commit; but you
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	303	can also make more specific requests:</p><div class="literallayout"><p>$ git log v2.5.. # commits since (not reachable from) v2.5<br>
				304	$ git log test..master # commits reachable from master but not test<br>
				305	$ git log master..test # ...reachable from test but not master<br>
				306	$ git log master...test # ...reachable from either test or master,<br>
				307	# but not both<br>
				308	$ git log --since="2 weeks ago" # commits from the last 2 weeks<br>
				309	$ git log Makefile # commits which modify Makefile<br>
				310	$ git log fs/ # ... which modify any file under fs/<br>
				311	$ git log -S'foo()' # commits which add or remove any file data<br>
				312	# matching the string 'foo()'</p></div><p>And of course you can combine all of these; the following finds
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	313	commits since v2.5 which touch the Makefile or any file under fs:</p><div class="literallayout"><p>$ git log v2.5.. Makefile fs/</p></div><p>You can also ask git log to show patches:</p><div class="literallayout"><p>$ git log -p</p></div><p>See the "—pretty" option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	314	display options.</p><p>Note that git log starts with the most recent commit and works
				315	backwards through the parents; however, since git history can contain
Junio C Hamano	ee1e428	2007-02-04 08:32:04	[diff] [blame]	316	multiple independent lines of development, the particular order that
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	317	commits are listed in may be somewhat arbitrary.</p></div><div class="section" title="Generating diffs"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generating-diffs"></a>Generating diffs</h2></div></div></div><p>You can generate diffs between any two versions using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	318	<a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>:</p><div class="literallayout"><p>$ git diff master..test</p></div><p>That will produce the diff between the tips of the two branches. If
Junio C Hamano	393e57f	2007-11-20 04:53:25	[diff] [blame]	319	you'd prefer to find the diff from their common ancestor to test, you
				320	can use three dots instead of two:</p><div class="literallayout"><p>$ git diff master...test</p></div><p>Sometimes what you want instead is a set of patches; for this you can
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	321	use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>:</p><div class="literallayout"><p>$ git format-patch master..test</p></div><p>will generate a file with a patch for each commit reachable from test
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	322	but not from master.</p></div><div class="section" title="Viewing old file versions"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="viewing-old-file-versions"></a>Viewing old file versions</h2></div></div></div><p>You can always view an old version of a file by just checking out the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	323	correct revision first. But sometimes it is more convenient to be
				324	able to view an old version of a single file without checking
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	325	anything out; this command does that:</p><div class="literallayout"><p>$ git show v2.5:fs/locks.c</p></div><p>Before the colon may be anything that names a commit, and after it
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	326	may be any path to a file tracked by git.</p></div><div class="section" title="Examples"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div><div class="section" title="Counting the number of commits on a branch"><div class="titlepage"><div><div><h3 class="title"><a name="counting-commits-on-a-branch"></a>Counting the number of commits on a branch</h3></div></div></div><p>Suppose you want to know how many commits you've made on "mybranch"
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	327	since it diverged from "origin":</p><div class="literallayout"><p>$ git log --pretty=oneline origin..mybranch \| wc -l</p></div><p>Alternatively, you may often see this sort of thing done with the
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	328	lower-level command <a class="ulink" href="git-rev-list.html" target="_top">git-rev-list(1)</a>, which just lists the SHA-1's
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	329	of all the given commits:</p><div class="literallayout"><p>$ git rev-list origin..mybranch \| wc -l</p></div></div><div class="section" title="Check whether two branches point at the same history"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-equal-branches"></a>Check whether two branches point at the same history</h3></div></div></div><p>Suppose you want to check whether two branches point at the same point
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	330	in history.</p><div class="literallayout"><p>$ git diff origin..master</p></div><p>will tell you whether the contents of the project are the same at the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	331	two branches; in theory, however, it's possible that the same project
				332	contents could have been arrived at by two different historical
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	333	routes. You could compare the object names:</p><div class="literallayout"><p>$ git rev-list origin<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	334	e05db0fd4f31dde7005f075a84f96b360d05984b<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	335	$ git rev-list master<br>
				336	e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>Or you could recall that the … operator selects all commits
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	337	contained reachable from either one reference or the other but not
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	338	both: so</p><div class="literallayout"><p>$ git log origin...master</p></div><p>will return no commits when the two branches are equal.</p></div><div class="section" title="Find first tagged version including a given fix"><div class="titlepage"><div><div><h3 class="title"><a name="finding-tagged-descendants"></a>Find first tagged version including a given fix</h3></div></div></div><p>Suppose you know that the commit e05db0fd fixed a certain problem.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	339	You'd like to find the earliest tagged release that contains that
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	340	fix.</p><p>Of course, there may be more than one answer—if the history branched
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	341	after commit e05db0fd, then there could be multiple "earliest" tagged
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	342	releases.</p><p>You could just visually inspect the commits since e05db0fd:</p><div class="literallayout"><p>$ gitk e05db0fd..</p></div><p>Or you can use <a class="ulink" href="git-name-rev.html" target="_top">git-name-rev(1)</a>, which will give the commit a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	343	name based on any tag it finds pointing to one of the commit's
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	344	descendants:</p><div class="literallayout"><p>$ git name-rev --tags e05db0fd<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	345	e05db0fd tags/v1.5.0-rc1^0~23</p></div><p>The <a class="ulink" href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	346	revision using a tag on which the given commit is based:</p><div class="literallayout"><p>$ git describe e05db0fd<br>
Junio C Hamano	4c6aa8a	2007-04-04 08:56:37	[diff] [blame]	347	v1.5.0-rc0-260-ge05db0f</p></div><p>but that may sometimes help you guess which tags might come after the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	348	given commit.</p><p>If you just want to verify whether a given tagged version contains a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	349	given commit, you could use <a class="ulink" href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p><div class="literallayout"><p>$ git merge-base e05db0fd v1.5.0-rc1<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	350	e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>The merge-base command finds a common ancestor of the given commits,
				351	and always returns one or the other in the case where one is a
				352	descendant of the other; so the above output shows that e05db0fd
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	353	actually is an ancestor of v1.5.0-rc1.</p><p>Alternatively, note that</p><div class="literallayout"><p>$ git log v1.5.0-rc1..e05db0fd</p></div><p>will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	354	because it outputs only commits that are not reachable from v1.5.0-rc1.</p><p>As yet another alternative, the <a class="ulink" href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	355	the commits reachable from its arguments with a display on the left-hand
				356	side that indicates which arguments that commit is reachable from. So,
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	357	you can run something like</p><div class="literallayout"><p>$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2<br>
				358	! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	359	available<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	360	! [v1.5.0-rc0] GIT v1.5.0 preview<br>
				361	! [v1.5.0-rc1] GIT v1.5.0-rc1<br>
				362	! [v1.5.0-rc2] GIT v1.5.0-rc2<br>
				363	...</p></div><p>then search for a line that looks like</p><div class="literallayout"><p>+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	364	available</p></div><p>Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	365	from v1.5.0-rc2, but not from v1.5.0-rc0.</p></div><div class="section" title="Showing commits unique to a given branch"><div class="titlepage"><div><div><h3 class="title"><a name="showing-commits-unique-to-a-branch"></a>Showing commits unique to a given branch</h3></div></div></div><p>Suppose you would like to see all the commits reachable from the branch
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	366	head named "master" but not from any other head in your repository.</p><p>We can list all the heads in this repository with
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	367	<a class="ulink" href="git-show-ref.html" target="_top">git-show-ref(1)</a>:</p><div class="literallayout"><p>$ git show-ref --heads<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	368	bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial<br>
				369	db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint<br>
				370	a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master<br>
				371	24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2<br>
				372	1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes</p></div><p>We can get just the branch-head names, and remove "master", with
				373	the help of the standard utilities cut and grep:</p><div class="literallayout"><p>$ git show-ref --heads \| cut -d' ' -f2 \| grep -v '^refs/heads/master'<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	374	refs/heads/core-tutorial<br>
				375	refs/heads/maint<br>
				376	refs/heads/tutorial-2<br>
				377	refs/heads/tutorial-fixes</p></div><p>And then we can ask to see all the commits reachable from master
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	378	but not from these other heads:</p><div class="literallayout"><p>$ gitk master --not $( git show-ref --heads \| cut -d' ' -f2 \|<br>
				379	grep -v '^refs/heads/master' )</p></div><p>Obviously, endless variations are possible; for example, to see all
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	380	commits reachable from some head but not from any tag in the repository:</p><div class="literallayout"><p>$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )</p></div><p>(See <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> for explanations of commit-selecting
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	381	syntax such as <code class="literal">—not</code>.)</p></div><div class="section" title="Creating a changelog and tarball for a software release"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div><p>The <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	382	any version of a project; for example:</p><div class="literallayout"><p>$ git archive --format=tar --prefix=project/ HEAD \| gzip >latest.tar.gz</p></div><p>will use HEAD to produce a tar archive in which each filename is
Junio C Hamano	2a8f6dc	2007-07-09 08:48:38	[diff] [blame]	383	preceded by "project/".</p><p>If you're releasing a new version of a software project, you may want
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	384	to simultaneously make a changelog to include in the release
				385	announcement.</p><p>Linus Torvalds, for example, makes new kernel releases by tagging them,
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	386	then running:</p><div class="literallayout"><p>$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7</p></div><p>where release-script is a shell script that looks like:</p><div class="literallayout"><p>#!/bin/sh<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	387	stable="$1"<br>
				388	last="$2"<br>
				389	new="$3"<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	390	echo "# git tag v$new"<br>
				391	echo "git archive --prefix=linux-$new/ v$new \| gzip -9 > ../linux-$new.tar.gz"<br>
				392	echo "git diff v$stable v$new \| gzip -9 > ../patch-$new.gz"<br>
				393	echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"<br>
				394	echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"<br>
				395	echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"</p></div><p>and then he just cut-and-pastes the output commands after verifying that
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	396	they look OK.</p></div><div class="section" title="Finding commits referencing a file with given content"><div class="titlepage"><div><div><h3 class="title"><a name="Finding-comments-With-given-Content"></a>Finding commits referencing a file with given content</h3></div></div></div><p>Somebody hands you a copy of a file, and asks which commits modified a
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	397	file such that it contained the given content either before or after the
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	398	commit. You can find out with this:</p><div class="literallayout"><p>$ git log --raw --abbrev=40 --pretty=oneline \|<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	399	grep -B 1 `git hash-object filename`</p></div><p>Figuring out why this works is left as an exercise to the (advanced)
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	400	student. The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a>, <a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	401	<a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a> man pages may prove helpful.</p></div></div></div><div class="chapter" title="Chapter 3. Developing with git"><div class="titlepage"><div><div><h2 class="title"><a name="Developing-With-git"></a>Chapter 3. Developing with git</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#telling-git-your-name">Telling git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></div><div class="section" title="Telling git your name"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="telling-git-your-name"></a>Telling git your name</h2></div></div></div><p>Before creating any commits, you should introduce yourself to git. The
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	402	easiest way to do so is to make sure the following lines appear in a
				403	file named .gitconfig in your home directory:</p><div class="literallayout"><p>[user]<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	404	name = Your Name Comes Here<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	405	email = you@yourdomain.example.com</p></div><p>(See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	406	details on the configuration file.)</p></div><div class="section" title="Creating a new repository"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-a-new-repository"></a>Creating a new repository</h2></div></div></div><p>Creating a new repository from scratch is very easy:</p><div class="literallayout"><p>$ mkdir project<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	407	$ cd project<br>
Junio C Hamano	4fbdd44	2009-01-06 05:56:24	[diff] [blame]	408	$ git init</p></div><p>If you have some initial content (say, a tarball):</p><div class="literallayout"><p>$ tar xzvf project.tar.gz<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	409	$ cd project<br>
				410	$ git init<br>
				411	$ git add . # include everything below ./ in the first commit:<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	412	$ git commit</p></div></div><div class="section" title="How to make a commit"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-make-a-commit"></a>How to make a commit</h2></div></div></div><p>Creating a new commit takes three steps:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	413	Making some changes to the working directory using your
				414	favorite editor.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	415	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	416	Telling git about your changes.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	417	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	418	Creating the commit using the content you told git about
				419	in step 2.
				420	</li></ol></div><p>In practice, you can interleave and repeat steps 1 and 2 as many
				421	times as you want: in order to keep track of what you want committed
				422	at step 3, git maintains a snapshot of the tree's contents in a
				423	special staging area called "the index."</p><p>At the beginning, the content of the index will be identical to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	424	that of the HEAD. The command "git diff —cached", which shows
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	425	the difference between the HEAD and the index, should therefore
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	426	produce no output at that point.</p><p>Modifying the index is easy:</p><p>To update the index with the new contents of a modified file, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To add the contents of a new file to the index, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To remove a file from the index and from the working tree,</p><div class="literallayout"><p>$ git rm path/to/file</p></div><p>After each step you can verify that</p><div class="literallayout"><p>$ git diff --cached</p></div><p>always shows the difference between the HEAD and the index file—this
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	427	is what you'd commit if you created the commit now—and that</p><div class="literallayout"><p>$ git diff</p></div><p>shows the difference between the working tree and the index file.</p><p>Note that "git add" always adds just the current contents of a file
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	428	to the index; further changes to the same file will be ignored unless
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	429	you run <code class="literal">git add</code> on the file again.</p><p>When you're ready, just run</p><div class="literallayout"><p>$ git commit</p></div><p>and git will prompt you for a commit message and then create the new
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	430	commit. Check to make sure it looks like what you expected with</p><div class="literallayout"><p>$ git show</p></div><p>As a special shortcut,</p><div class="literallayout"><p>$ git commit -a</p></div><p>will update the index with any files that you've modified or removed
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	431	and create a commit, all in one step.</p><p>A number of commands are useful for keeping track of what you're
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	432	about to commit:</p><div class="literallayout"><p>$ git diff --cached # difference between HEAD and the index; what<br>
				433	# would be committed if you ran "commit" now.<br>
				434	$ git diff # difference between the index file and your<br>
				435	# working directory; changes that would not<br>
				436	# be included if you ran "commit" now.<br>
				437	$ git diff HEAD # difference between HEAD and working tree; what<br>
				438	# would be committed if you ran "commit -a" now.<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	439	$ git status # a brief per-file summary of the above.</p></div><p>You can also use <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> to create commits, view changes in
Junio C Hamano	4cd1c0e	2007-08-06 04:39:14	[diff] [blame]	440	the index and the working tree files, and individually select diff hunks
				441	for inclusion in the index (by right-clicking on the diff hunk and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	442	choosing "Stage Hunk For Commit").</p></div><div class="section" title="Creating good commit messages"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-good-commit-messages"></a>Creating good commit messages</h2></div></div></div><p>Though not required, it's a good idea to begin the commit message
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	443	with a single short (less than 50 character) line summarizing the
				444	change, followed by a blank line and then a more thorough
				445	description. Tools that turn commits into email, for example, use
				446	the first line on the Subject line and the rest of the commit in the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	447	body.</p></div><div class="section" title="Ignoring files"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ignoring-files"></a>Ignoring files</h2></div></div></div><p>A project will often generate files that you do <span class="emphasis"><em>not</em></span> want to track with git.
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	448	This typically includes files generated by a build process or temporary
				449	backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with git
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	450	is just a matter of <span class="emphasis"><em>not</em></span> calling <code class="literal">git add</code> on them. But it quickly becomes
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	451	annoying to have these untracked files lying around; e.g. they make
Junio C Hamano	ea82cff	2009-03-18 01:54:48	[diff] [blame]	452	<code class="literal">git add .</code> practically useless, and they keep showing up in the output of
				453	<code class="literal">git status</code>.</p><p>You can tell git to ignore certain files by creating a file called .gitignore
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	454	in the top level of your working directory, with contents such as:</p><div class="literallayout"><p># Lines starting with '#' are considered comments.<br>
				455	# Ignore any file named foo.txt.<br>
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	456	foo.txt<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	457	# Ignore (generated) html files,<br>
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	458	*.html<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	459	# except foo.html which is maintained by hand.<br>
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	460	!foo.html<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	461	# Ignore objects and archives.<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	462	*.[oa]</p></div><p>See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for a detailed explanation of the syntax. You can
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	463	also place .gitignore files in other directories in your working tree, and they
				464	will apply to those directories and their subdirectories. The <code class="literal">.gitignore</code>
				465	files can be added to your repository like any other files (just run <code class="literal">git add
				466	.gitignore</code> and <code class="literal">git commit</code>, as usual), which is convenient when the exclude
				467	patterns (such as patterns matching build output files) would also make sense
				468	for other users who clone your repository.</p><p>If you wish the exclude patterns to affect only certain repositories
				469	(instead of every repository for a given project), you may instead put
				470	them in a file in your repository named .git/info/exclude, or in any file
				471	specified by the <code class="literal">core.excludesfile</code> configuration variable. Some git
				472	commands can also take exclude patterns directly on the command line.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	473	See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for the details.</p></div><div class="section" title="How to merge"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-merge"></a>How to merge</h2></div></div></div><p>You can rejoin two diverging branches of development using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	474	<a class="ulink" href="git-merge.html" target="_top">git-merge(1)</a>:</p><div class="literallayout"><p>$ git merge branchname</p></div><p>merges the development in the branch "branchname" into the current
Junio C Hamano	5706e0b	2009-11-24 10:54:16	[diff] [blame]	475	branch.</p><p>A merge is made by combining the changes made in "branchname" and the
				476	changes made up to the latest commit in your current branch since
				477	their histories forked. The work tree is overwritten by the result of
				478	the merge when this combining is done cleanly, or overwritten by a
				479	half-merged results when this combining results in conflicts.
				480	Therefore, if you have uncommitted changes touching the same files as
				481	the ones impacted by the merge, Git will refuse to proceed. Most of
				482	the time, you will want to commit your changes before you can merge,
				483	and if you don't, then <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> can take these changes
Junio C Hamano	167b138	2010-01-31 23:04:31	[diff] [blame]	484	away while you're doing the merge, and reapply them afterwards.</p><p>If the changes are independent enough, Git will automatically complete
Junio C Hamano	5706e0b	2009-11-24 10:54:16	[diff] [blame]	485	the merge and commit the result (or reuse an existing commit in case
				486	of <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>, see below). On the other hand,
				487	if there are conflicts—for example, if the same file is
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	488	modified in two different ways in the remote branch and the local
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	489	branch—then you are warned; the output may look something like this:</p><div class="literallayout"><p>$ git merge next<br>
				490	100% (4/4) done<br>
				491	Auto-merged file.txt<br>
				492	CONFLICT (content): Merge conflict in file.txt<br>
				493	Automatic merge failed; fix conflicts and then commit the result.</p></div><p>Conflict markers are left in the problematic files, and after
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	494	you resolve the conflicts manually, you can update the index
				495	with the contents and run git commit, as you normally would when
				496	creating a new file.</p><p>If you examine the resulting commit using gitk, you will see that it
				497	has two parents, one pointing to the top of the current branch, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	498	one to the top of the other branch.</p></div><div class="section" title="Resolving a merge"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="resolving-a-merge"></a>Resolving a merge</h2></div></div></div><p>When a merge isn't resolved automatically, git leaves the index and
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	499	the working tree in a special state that gives you all the
				500	information you need to help resolve the merge.</p><p>Files with conflicts are marked specially in the index, so until you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	501	resolve the problem and update the index, <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> will
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	502	fail:</p><div class="literallayout"><p>$ git commit<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	503	file.txt: needs merge</p></div><p>Also, <a class="ulink" href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	504	files with conflicts will have conflict markers added, like this:</p><div class="literallayout"><p><<<<<<< HEAD:file.txt<br>
				505	Hello world<br>
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	506	=======<br>
				507	Goodbye<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	508	>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>All you need to do is edit the files to resolve the conflicts, and then</p><div class="literallayout"><p>$ git add file.txt<br>
				509	$ git commit</p></div><p>Note that the commit message will already be filled in for you with
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	510	some information about the merge. Normally you can just use this
				511	default message unchanged, but you may add additional commentary of
				512	your own if desired.</p><p>The above is all you need to know to resolve a simple merge. But git
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	513	also provides more information to help resolve conflicts:</p><div class="section" title="Getting conflict-resolution help during a merge"><div class="titlepage"><div><div><h3 class="title"><a name="conflict-resolution"></a>Getting conflict-resolution help during a merge</h3></div></div></div><p>All of the changes that git was able to merge automatically are
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	514	already added to the index file, so <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> shows only
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	515	the conflicts. It uses an unusual syntax:</p><div class="literallayout"><p>$ git diff<br>
				516	diff --cc file.txt<br>
				517	index 802992c,2b60207..0000000<br>
				518	--- a/file.txt<br>
				519	+++ b/file.txt<br>
				520	@@@ -1,1 -1,1 +1,5 @@@<br>
				521	++<<<<<<< HEAD:file.txt<br>
				522	+Hello world<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	523	++=======<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	524	+ Goodbye<br>
				525	++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>Recall that the commit which will be committed after we resolve this
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	526	conflict will have two parents instead of the usual one: one parent
				527	will be HEAD, the tip of the current branch; the other will be the
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	528	tip of the other branch, which is stored temporarily in MERGE_HEAD.</p><p>During the merge, the index holds three versions of each file. Each of
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	529	these three "file stages" represents a different version of the file:</p><div class="literallayout"><p>$ git show :1:file.txt # the file in a common ancestor of both branches<br>
Junio C Hamano	6fb124c	2008-06-13 10:04:01	[diff] [blame]	530	$ git show :2:file.txt # the version from HEAD.<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	531	$ git show :3:file.txt # the version from MERGE_HEAD.</p></div><p>When you ask <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the conflicts, it runs a
Junio C Hamano	6fb124c	2008-06-13 10:04:01	[diff] [blame]	532	three-way diff between the conflicted merge results in the work tree with
				533	stages 2 and 3 to show only hunks whose contents come from both sides,
				534	mixed (in other words, when a hunk's merge results come only from stage 2,
				535	that part is not conflicting and is not shown. Same for stage 3).</p><p>The diff above shows the differences between the working-tree version of
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	536	file.txt and the stage 2 and stage 3 versions. So instead of preceding
				537	each line by a single "+" or "-", it now uses two columns: the first
				538	column is used for differences between the first parent and the working
				539	directory copy, and the second for differences between the second parent
				540	and the working directory copy. (See the "COMBINED DIFF FORMAT" section
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	541	of <a class="ulink" href="git-diff-files.html" target="_top">git-diff-files(1)</a> for a details of the format.)</p><p>After resolving the conflict in the obvious way (but before updating the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	542	index), the diff will look like:</p><div class="literallayout"><p>$ git diff<br>
				543	diff --cc file.txt<br>
				544	index 802992c,2b60207..0000000<br>
				545	--- a/file.txt<br>
				546	+++ b/file.txt<br>
				547	@@@ -1,1 -1,1 +1,1 @@@<br>
				548	- Hello world<br>
				549	-Goodbye<br>
				550	++Goodbye world</p></div><p>This shows that our resolved version deleted "Hello world" from the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	551	first parent, deleted "Goodbye" from the second parent, and added
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	552	"Goodbye world", which was previously absent from both.</p><p>Some special diff options allow diffing the working directory against
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	553	any of these stages:</p><div class="literallayout"><p>$ git diff -1 file.txt # diff against stage 1<br>
				554	$ git diff --base file.txt # same as the above<br>
				555	$ git diff -2 file.txt # diff against stage 2<br>
				556	$ git diff --ours file.txt # same as the above<br>
				557	$ git diff -3 file.txt # diff against stage 3<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	558	$ git diff --theirs file.txt # same as the above.</p></div><p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> and <a class="ulink" href="gitk.html" target="_top">gitk(1)</a> commands also provide special help
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	559	for merges:</p><div class="literallayout"><p>$ git log --merge<br>
				560	$ gitk --merge</p></div><p>These will display all commits which exist only on HEAD or on
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	561	MERGE_HEAD, and which touch an unmerged file.</p><p>You may also use <a class="ulink" href="git-mergetool.html" target="_top">git-mergetool(1)</a>, which lets you merge the
Junio C Hamano	4fbdd44	2009-01-06 05:56:24	[diff] [blame]	562	unmerged files using external tools such as Emacs or kdiff3.</p><p>Each time you resolve the conflicts in a file and update the index:</p><div class="literallayout"><p>$ git add file.txt</p></div><p>the different stages of that file will be "collapsed", after which
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	563	<code class="literal">git diff</code> will (by default) no longer show diffs for that file.</p></div></div><div class="section" title="Undoing a merge"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="undoing-a-merge"></a>Undoing a merge</h2></div></div></div><p>If you get stuck and decide to just give up and throw the whole mess
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	564	away, you can always return to the pre-merge state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>Or, if you've already committed the merge that you want to throw away,</p><div class="literallayout"><p>$ git reset --hard ORIG_HEAD</p></div><p>However, this last command can be dangerous in some cases—never
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	565	throw away a commit you have already committed if that commit may
				566	itself have been merged into another branch, as doing so may confuse
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	567	further merges.</p></div><div class="section" title="Fast-forward merges"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fast-forwards"></a>Fast-forward merges</h2></div></div></div><p>There is one special case not mentioned above, which is treated
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	568	differently. Normally, a merge results in a merge commit, with two
				569	parents, one pointing at each of the two lines of development that
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	570	were merged.</p><p>However, if the current branch is a descendant of the other—so every
				571	commit present in the one is already contained in the other—then git
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	572	just performs a "fast-forward"; the head of the current branch is moved
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	573	forward to point at the head of the merged-in branch, without any new
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	574	commits being created.</p></div><div class="section" title="Fixing mistakes"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fixing-mistakes"></a>Fixing mistakes</h2></div></div></div><p>If you've messed up the working tree, but haven't yet committed your
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	575	mistake, you can return the entire working tree to the last committed
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	576	state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>If you make a commit that you later wish you hadn't, there are two
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	577	fundamentally different ways to fix the problem:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	578	You can create a new commit that undoes whatever was done
Junio C Hamano	8c5802d	2007-11-15 00:13:36	[diff] [blame]	579	by the old commit. This is the correct thing if your
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	580	mistake has already been made public.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	581	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	582	You can go back and modify the old commit. You should
				583	never do this if you have already made the history public;
				584	git does not normally expect the "history" of a project to
				585	change, and cannot correctly perform repeated merges from
				586	a branch that has had its history changed.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	587	</li></ol></div><div class="section" title="Fixing a mistake with a new commit"><div class="titlepage"><div><div><h3 class="title"><a name="reverting-a-commit"></a>Fixing a mistake with a new commit</h3></div></div></div><p>Creating a new commit that reverts an earlier change is very easy;
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	588	just pass the <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	589	commit; for example, to revert the most recent commit:</p><div class="literallayout"><p>$ git revert HEAD</p></div><p>This will create a new commit which undoes the change in HEAD. You
				590	will be given a chance to edit the commit message for the new commit.</p><p>You can also revert an earlier change, for example, the next-to-last:</p><div class="literallayout"><p>$ git revert HEAD^</p></div><p>In this case git will attempt to undo the old change while leaving
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	591	intact any changes made since then. If more recent changes overlap
				592	with the changes to be reverted, then you will be asked to fix
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	593	conflicts manually, just as in the case of <a class="link" href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p></div><div class="section" title="Fixing a mistake by rewriting history"><div class="titlepage"><div><div><h3 class="title"><a name="fixing-a-mistake-by-rewriting-history"></a>Fixing a mistake by rewriting history</h3></div></div></div><p>If the problematic commit is the most recent commit, and you have not
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	594	yet made that commit public, then you may just
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	595	<a class="link" href="#undoing-a-merge" title="Undoing a merge">destroy it using <code class="literal">git reset</code></a>.</p><p>Alternatively, you
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	596	can edit the working directory and update the index to fix your
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	597	mistake, just as if you were going to <a class="link" href="#how-to-make-a-commit" title="How to make a commit">create a new commit</a>, then run</p><div class="literallayout"><p>$ git commit --amend</p></div><p>which will replace the old commit by a new commit incorporating your
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	598	changes, giving you a chance to edit the old commit message first.</p><p>Again, you should never do this to a commit that may already have
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	599	been merged into another branch; use <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> instead in
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	600	that case.</p><p>It is also possible to replace commits further back in the history, but
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	601	this is an advanced topic to be left for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	602	<a class="link" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">another chapter</a>.</p></div><div class="section" title="Checking out an old version of a file"><div class="titlepage"><div><div><h3 class="title"><a name="checkout-of-path"></a>Checking out an old version of a file</h3></div></div></div><p>In the process of undoing a previous bad change, you may find it
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	603	useful to check out an older version of a particular file using
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	604	<a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>. We've used <code class="literal">git checkout</code> before to switch
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	605	branches, but it has quite different behavior if it is given a path
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	606	name: the command</p><div class="literallayout"><p>$ git checkout HEAD^ path/to/file</p></div><p>replaces path/to/file by the contents it had in the commit HEAD^, and
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	607	also updates the index to match. It does not change branches.</p><p>If you just want to look at an old version of the file, without
				608	modifying the working directory, you can do that with
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	609	<a class="ulink" href="git-show.html" target="_top">git-show(1)</a>:</p><div class="literallayout"><p>$ git show HEAD^:path/to/file</p></div><p>which will display the given version of the file.</p></div><div class="section" title="Temporarily setting aside work in progress"><div class="titlepage"><div><div><h3 class="title"><a name="interrupted-work"></a>Temporarily setting aside work in progress</h3></div></div></div><p>While you are in the middle of working on something complicated, you
Junio C Hamano	4cd1c0e	2007-08-06 04:39:14	[diff] [blame]	610	find an unrelated but obvious and trivial bug. You would like to fix it
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	611	before continuing. You can use <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> to save the current
Junio C Hamano	4cd1c0e	2007-08-06 04:39:14	[diff] [blame]	612	state of your work, and after fixing the bug (or, optionally after doing
				613	so on a different branch and then coming back), unstash the
Junio C Hamano	7850245	2009-02-04 16:53:50	[diff] [blame]	614	work-in-progress changes.</p><div class="literallayout"><p>$ git stash save "work in progress for foo feature"</p></div><p>This command will save your changes away to the <code class="literal">stash</code>, and
Junio C Hamano	4cd1c0e	2007-08-06 04:39:14	[diff] [blame]	615	reset your working tree and the index to match the tip of your
				616	current branch. Then you can make your fix as usual.</p><div class="literallayout"><p>... edit and test ...<br>
				617	$ git commit -a -m "blorpl: typofix"</p></div><p>After that, you can go back to what you were working on with
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	618	<code class="literal">git stash pop</code>:</p><div class="literallayout"><p>$ git stash pop</p></div></div></div><div class="section" title="Ensuring good performance"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-good-performance"></a>Ensuring good performance</h2></div></div></div><p>On large repositories, git depends on compression to keep the history
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	619	information from taking up too much space on disk or in memory.</p><p>This compression is not performed automatically. Therefore you
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	620	should occasionally run <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a>:</p><div class="literallayout"><p>$ git gc</p></div><p>to recompress the archive. This can be very time-consuming, so
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	621	you may prefer to run <code class="literal">git gc</code> when you are not doing other work.</p></div><div class="section" title="Ensuring reliability"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-reliability"></a>Ensuring reliability</h2></div></div></div><div class="section" title="Checking the repository for corruption"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-corruption"></a>Checking the repository for corruption</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	622	on the repository, and reports on any problems. This may take some
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	623	time. The most common warning by far is about "dangling" objects:</p><div class="literallayout"><p>$ git fsck<br>
				624	dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br>
				625	dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br>
				626	dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br>
				627	dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb<br>
				628	dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f<br>
				629	dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e<br>
				630	dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085<br>
				631	dangling tree b24c2473f1fd3d91352a624795be026d64c8841f<br>
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	632	...</p></div><p>Dangling objects are not a problem. At worst they may take up a little
Junio C Hamano	2a8f6dc	2007-07-09 08:48:38	[diff] [blame]	633	extra disk space. They can sometimes provide a last-resort method for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	634	recovering lost work—see <a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for details.</p></div><div class="section" title="Recovering lost changes"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-lost-changes"></a>Recovering lost changes</h3></div></div></div><div class="section" title="Reflogs"><div class="titlepage"><div><div><h4 class="title"><a name="reflogs"></a>Reflogs</h4></div></div></div><p>Say you modify a branch with <code class="literal"><a class="ulink" href="git-reset.html" target="_top">git-reset(1)</a> —hard</code>, and then
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	635	realize that the branch was the only reference you had to that point in
				636	history.</p><p>Fortunately, git also keeps a log, called a "reflog", of all the
				637	previous values of each branch. So in this case you can still find the
Junio C Hamano	63777e2	2007-11-17 20:52:16	[diff] [blame]	638	old history using, for example,</p><div class="literallayout"><p>$ git log master@{1}</p></div><p>This lists the commits reachable from the previous version of the
				639	"master" branch head. This syntax can be used with any git command
				640	that accepts a commit, not just with git log. Some other examples:</p><div class="literallayout"><p>$ git show master@{2} # See where the branch pointed 2,<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	641	$ git show master@{3} # 3, ... changes ago.<br>
				642	$ gitk master@{yesterday} # See where it pointed yesterday,<br>
				643	$ gitk master@{"1 week ago"} # ... or last week<br>
				644	$ git log --walk-reflogs master # show reflog entries for master</p></div><p>A separate reflog is kept for the HEAD, so</p><div class="literallayout"><p>$ git show HEAD@{"1 week ago"}</p></div><p>will show what HEAD pointed to one week ago, not what the current branch
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	645	pointed to one week ago. This allows you to see the history of what
				646	you've checked out.</p><p>The reflogs are kept by default for 30 days, after which they may be
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	647	pruned. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> and <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> to learn
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	648	how to control this pruning, and see the "SPECIFYING REVISIONS"
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	649	section of <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> for details.</p><p>Note that the reflog history is very different from normal git history.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	650	While normal history is shared by every repository that works on the
				651	same project, the reflog history is not shared: it tells you only about
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	652	how the branches in your local repository have changed over time.</p></div><div class="section" title="Examining dangling objects"><div class="titlepage"><div><div><h4 class="title"><a name="dangling-object-recovery"></a>Examining dangling objects</h4></div></div></div><p>In some situations the reflog may not be able to save you. For example,
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	653	suppose you delete a branch, then realize you need the history it
				654	contained. The reflog is also deleted; however, if you have not yet
				655	pruned the repository, then you may still be able to find the lost
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	656	commits in the dangling objects that <code class="literal">git fsck</code> reports. See
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	657	<a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for the details.</p><div class="literallayout"><p>$ git fsck<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	658	dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br>
				659	dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br>
				660	dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br>
Junio C Hamano	39381a7	2007-02-02 07:35:15	[diff] [blame]	661	...</p></div><p>You can examine
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	662	one of those dangling commits with, for example,</p><div class="literallayout"><p>$ gitk 7281251ddd --not --all</p></div><p>which does what it sounds like: it says that you want to see the commit
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	663	history that is described by the dangling commit(s), but not the
				664	history that is described by all your existing branches and tags. Thus
				665	you get exactly the history reachable from that commit that is lost.
				666	(And notice that it might not be just one commit: we only report the
				667	"tip of the line" as being dangling, but there might be a whole deep
Junio C Hamano	db911ee	2007-02-28 08:13:52	[diff] [blame]	668	and complex commit history that was dropped.)</p><p>If you decide you want the history back, you can always create a new
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	669	reference pointing to it, for example, a new branch:</p><div class="literallayout"><p>$ git branch recovered-branch 7281251ddd</p></div><p>Other types of dangling objects (blobs and trees) are also possible, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	670	dangling objects can arise in other situations.</p></div></div></div></div><div class="chapter" title="Chapter 4. Sharing development with others"><div class="titlepage"><div><div><h2 class="title"><a name="sharing-development"></a>Chapter 4. Sharing development with others</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a git repository via the git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via http</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></div><div class="section" title="Getting updates with git pull"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="getting-updates-With-git-pull"></a>Getting updates with git pull</h2></div></div></div><p>After you clone a repository and commit a few changes of your own, you
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	671	may wish to check the original repository for updates and merge them
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	672	into your own work.</p><p>We have already seen <a class="link" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">how to keep remote tracking branches up to date</a> with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>,
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	673	and how to merge two branches. So you can merge in changes from the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	674	original repository's master branch with:</p><div class="literallayout"><p>$ git fetch<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	675	$ git merge origin/master</p></div><p>However, the <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in
Junio C Hamano	4cd1c0e	2007-08-06 04:39:14	[diff] [blame]	676	one step:</p><div class="literallayout"><p>$ git pull origin master</p></div><p>In fact, if you have "master" checked out, then by default "git pull"
				677	merges from the HEAD branch of the origin repository. So often you can
				678	accomplish the above with just a simple</p><div class="literallayout"><p>$ git pull</p></div><p>More generally, a branch that is created from a remote branch will pull
				679	by default from that branch. See the descriptions of the
				680	branch.<name>.remote and branch.<name>.merge options in
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	681	<a class="ulink" href="git-config.html" target="_top">git-config(1)</a>, and the discussion of the <code class="literal">—track</code> option in
				682	<a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>, to learn how to control these defaults.</p><p>In addition to saving you keystrokes, "git pull" also helps you by
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	683	producing a default commit message documenting the branch and
				684	repository that you pulled from.</p><p>(But note that no such commit will be created in the case of a
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	685	<a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; instead, your branch will just be
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	686	updated to point to the latest commit from the upstream branch.)</p><p>The <code class="literal">git pull</code> command can also be given "." as the "remote" repository,
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	687	in which case it just merges in a branch from the current repository; so
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	688	the commands</p><div class="literallayout"><p>$ git pull . branch<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	689	$ git merge branch</p></div><p>are roughly equivalent. The former is actually very commonly used.</p></div><div class="section" title="Submitting patches to a project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="submitting-patches"></a>Submitting patches to a project</h2></div></div></div><p>If you just have a few changes, the simplest way to submit them may
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	690	just be to send them as patches in email:</p><p>First, use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>; for example:</p><div class="literallayout"><p>$ git format-patch origin</p></div><p>will produce a numbered series of files in the current directory, one
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	691	for each patch in the current branch but not in origin/HEAD.</p><p>You can then import these into your mail client and send them by
				692	hand. However, if you have a lot to send at once, you may prefer to
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	693	use the <a class="ulink" href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	694	Consult the mailing list for your project first to determine how they
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	695	prefer such patches be handled.</p></div><div class="section" title="Importing patches to a project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="importing-patches"></a>Importing patches to a project</h2></div></div></div><p>Git also provides a tool called <a class="ulink" href="git-am.html" target="_top">git-am(1)</a> (am stands for
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	696	"apply mailbox"), for importing such an emailed series of patches.
				697	Just save all of the patch-containing messages, in order, into a
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	698	single mailbox file, say "patches.mbox", then run</p><div class="literallayout"><p>$ git am -3 patches.mbox</p></div><p>Git will apply each patch in order; if any conflicts are found, it
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	699	will stop, and you can fix the conflicts as described in
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	700	"<a class="link" href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The "-3" option tells
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	701	git to perform a merge; if you would prefer it just to abort and
				702	leave your tree and index untouched, you may omit that option.)</p><p>Once the index is updated with the results of the conflict
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	703	resolution, instead of creating a new commit, just run</p><div class="literallayout"><p>$ git am --resolved</p></div><p>and git will create the commit for you and continue applying the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	704	remaining patches from the mailbox.</p><p>The final result will be a series of commits, one for each patch in
				705	the original mailbox, with authorship and commit log message each
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	706	taken from the message containing each patch.</p></div><div class="section" title="Public git repositories"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="public-repositories"></a>Public git repositories</h2></div></div></div><p>Another way to submit changes to a project is to tell the maintainer
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	707	of that project to pull the changes from your repository using
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	708	<a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>. In the section "<a class="link" href="#getting-updates-With-git-pull" title="Getting updates with git pull">Getting updates with <code class="literal">git pull</code></a>" we described this as a way to get
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	709	updates from the "main" repository, but it works just as well in the
				710	other direction.</p><p>If you and the maintainer both have accounts on the same machine, then
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	711	you can just pull changes from each other's repositories directly;
Junio C Hamano	2a8f6dc	2007-07-09 08:48:38	[diff] [blame]	712	commands that accept repository URLs as arguments will also accept a
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	713	local directory name:</p><div class="literallayout"><p>$ git clone /path/to/repository<br>
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	714	$ git pull /path/to/other/repository</p></div><p>or an ssh URL:</p><div class="literallayout"><p>$ git clone ssh://yourhost/~you/repository</p></div><p>For projects with few developers, or for synchronizing a few private
Junio C Hamano	2a8f6dc	2007-07-09 08:48:38	[diff] [blame]	715	repositories, this may be all you need.</p><p>However, the more common way to do this is to maintain a separate public
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	716	repository (usually on a different host) for others to pull changes
				717	from. This is usually more convenient, and allows you to cleanly
				718	separate private work in progress from publicly visible work.</p><p>You will continue to do your day-to-day work in your personal
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	719	repository, but periodically "push" changes from your personal
				720	repository into your public repository, allowing other developers to
				721	pull from that repository. So the flow of changes, in a situation
				722	where there is one other developer with a public repository, looks
				723	like this:</p><pre class="literallayout"> you push
				724	your personal repo ------------------> your public repo
				725	^ \|
				726	\| \|
				727	\| you pull \| they pull
				728	\| \|
				729	\| \|
				730	\| they push V
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	731	their public repo <------------------- their repo</pre><p>We explain how to do this in the following sections.</p><div class="section" title="Setting up a public repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-public-repository"></a>Setting up a public repository</h3></div></div></div><p>Assume your personal repository is in the directory ~/proj. We
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	732	first create a new clone of the repository and tell <code class="literal">git daemon</code> that it
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	733	is meant to be public:</p><div class="literallayout"><p>$ git clone --bare ~/proj proj.git<br>
				734	$ touch proj.git/git-daemon-export-ok</p></div><p>The resulting directory proj.git contains a "bare" git repository—it is
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	735	just the contents of the ".git" directory, without any files checked out
				736	around it.</p><p>Next, copy proj.git to the server where you plan to host the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	737	public repository. You can use scp, rsync, or whatever is most
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	738	convenient.</p></div><div class="section" title="Exporting a git repository via the git protocol"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-git"></a>Exporting a git repository via the git protocol</h3></div></div></div><p>This is the preferred method.</p><p>If someone else administers the server, they should tell you what
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	739	directory to put the repository in, and what git:// URL it will appear
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	740	at. You can then skip to the section
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	741	"<a class="link" href="#pushing-changes-to-a-public-repository" title="Pushing changes to a public repository">Pushing changes to a public repository</a>", below.</p><p>Otherwise, all you need to do is start <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a>; it will
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	742	listen on port 9418. By default, it will allow access to any directory
				743	that looks like a git directory and contains the magic file
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	744	git-daemon-export-ok. Passing some directory paths as <code class="literal">git daemon</code>
				745	arguments will further restrict the exports to those paths.</p><p>You can also run <code class="literal">git daemon</code> as an inetd service; see the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	746	<a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a> man page for details. (See especially the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	747	examples section.)</p></div><div class="section" title="Exporting a git repository via http"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-http"></a>Exporting a git repository via http</h3></div></div></div><p>The git protocol gives better performance and reliability, but on a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	748	host with a web server set up, http exports may be simpler to set up.</p><p>All you need to do is place the newly created bare git repository in
				749	a directory that is exported by the web server, and make some
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	750	adjustments to give web clients some extra information they need:</p><div class="literallayout"><p>$ mv proj.git /home/you/public_html/proj.git<br>
				751	$ cd proj.git<br>
				752	$ git --bare update-server-info<br>
Junio C Hamano	c96fb5a	2008-08-12 06:59:38	[diff] [blame]	753	$ mv hooks/post-update.sample hooks/post-update</p></div><p>(For an explanation of the last two lines, see
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	754	<a class="ulink" href="git-update-server-info.html" target="_top">git-update-server-info(1)</a> and <a class="ulink" href="githooks.html" target="_top">githooks(5)</a>.)</p><p>Advertise the URL of proj.git. Anybody else should then be able to
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	755	clone or pull from that URL, for example with a command line like:</p><div class="literallayout"><p>$ git clone http://yourserver.com/~you/proj.git</p></div><p>(See also
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	756	<a class="ulink" href="howto/setup-git-server-over-http.txt" target="_top">setup-git-server-over-http</a>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	757	for a slightly more sophisticated setup using WebDAV which also
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	758	allows pushing over http.)</p></div><div class="section" title="Pushing changes to a public repository"><div class="titlepage"><div><div><h3 class="title"><a name="pushing-changes-to-a-public-repository"></a>Pushing changes to a public repository</h3></div></div></div><p>Note that the two techniques outlined above (exporting via
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	759	<a class="link" href="#exporting-via-http" title="Exporting a git repository via http">http</a> or <a class="link" href="#exporting-via-git" title="Exporting a git repository via the git protocol">git</a>) allow other
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	760	maintainers to fetch your latest changes, but they do not allow write
				761	access, which you will need to update the public repository with the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	762	latest changes created in your private repository.</p><p>The simplest way to do this is using <a class="ulink" href="git-push.html" target="_top">git-push(1)</a> and ssh; to
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	763	update the remote branch named "master" with the latest state of your
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	764	branch named "master", run</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master:master</p></div><p>or just</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master</p></div><p>As with <code class="literal">git fetch</code>, <code class="literal">git push</code> will complain if this does not result in a
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	765	<a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; see the following section for details on
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	766	handling this case.</p><p>Note that the target of a "push" is normally a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	767	<a class="link" href="#def_bare_repository">bare</a> repository. You can also push to a
Junio C Hamano	2a8f6dc	2007-07-09 08:48:38	[diff] [blame]	768	repository that has a checked-out working tree, but the working tree
				769	will not be updated by the push. This may lead to unexpected results if
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	770	the branch you push to is the currently checked-out branch!</p><p>As with <code class="literal">git fetch</code>, you may also set up configuration options to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	771	save typing; so, for example, after</p><div class="literallayout"><p>$ cat >>.git/config <<EOF<br>
				772	[remote "public-repo"]<br>
				773	url = ssh://yourserver.com/~you/proj.git<br>
				774	EOF</p></div><p>you should be able to perform the above push with just</p><div class="literallayout"><p>$ git push public-repo master</p></div><p>See the explanations of the remote.<name>.url, branch.<name>.remote,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	775	and remote.<name>.push options in <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	776	details.</p></div><div class="section" title="What to do when a push fails"><div class="titlepage"><div><div><h3 class="title"><a name="forcing-push"></a>What to do when a push fails</h3></div></div></div><p>If a push would not result in a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> of the
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	777	remote branch, then it will fail with an error like:</p><div class="literallayout"><p>error: remote 'refs/heads/master' is not an ancestor of<br>
				778	local 'refs/heads/master'.<br>
				779	Maybe you are not up-to-date and need to pull first?<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	780	error: failed to push to 'ssh://yourserver.com/~you/proj.git'</p></div><p>This can happen, for example, if you:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	781	use <code class="literal">git reset —hard</code> to remove already-published commits, or
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	782	</li><li class="listitem">
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	783	use <code class="literal">git commit —amend</code> to replace already-published commits
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	784	(as in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a>), or
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	785	</li><li class="listitem">
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	786	use <code class="literal">git rebase</code> to rebase any already-published commits (as
				787	in <a class="xref" href="#using-git-rebase" title="Keeping a patch series up to date using git rebase">the section called “Keeping a patch series up to date using git rebase”</a>).
				788	</li></ul></div><p>You may force <code class="literal">git push</code> to perform the update anyway by preceding the
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	789	branch name with a plus sign:</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git +master</p></div><p>Normally whenever a branch head in a public repository is modified, it
Junio C Hamano	878cc1e	2007-12-14 08:35:13	[diff] [blame]	790	is modified to point to a descendant of the commit that it pointed to
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	791	before. By forcing a push in this situation, you break that convention.
Junio C Hamano	ec87f52	2008-12-10 08:35:25	[diff] [blame]	792	(See <a class="xref" href="#problems-With-rewriting-history" title="Problems with rewriting history">the section called “Problems with rewriting history”</a>.)</p><p>Nevertheless, this is a common practice for people that need a simple
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	793	way to publish a work-in-progress patch series, and it is an acceptable
				794	compromise as long as you warn other developers that this is how you
				795	intend to manage the branch.</p><p>It's also possible for a push to fail in this way when other people have
				796	the right to push to the same repository. In that case, the correct
Junio C Hamano	d32738e	2008-07-09 19:53:42	[diff] [blame]	797	solution is to retry the push after first updating your work: either by a
				798	pull, or by a fetch followed by a rebase; see the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	799	<a class="link" href="#setting-up-a-shared-repository" title="Setting up a shared repository">next section</a> and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	800	<a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for more.</p></div><div class="section" title="Setting up a shared repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-shared-repository"></a>Setting up a shared repository</h3></div></div></div><p>Another way to collaborate is by using a model similar to that
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	801	commonly used in CVS, where several developers with special rights
				802	all push to and pull from a single shared repository. See
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	803	<a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for instructions on how to
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	804	set this up.</p><p>However, while there is nothing wrong with git's support for shared
				805	repositories, this mode of operation is not generally recommended,
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	806	simply because the mode of collaboration that git supports—by
				807	exchanging patches and pulling from public repositories—has so many
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	808	advantages over the central shared repository:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	809	Git's ability to quickly import and merge patches allows a
				810	single maintainer to process incoming changes even at very
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	811	high rates. And when that becomes too much, <code class="literal">git pull</code> provides
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	812	an easy way for that maintainer to delegate this job to other
				813	maintainers while still allowing optional review of incoming
				814	changes.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	815	</li><li class="listitem">
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	816	Since every developer's repository has the same complete copy
				817	of the project history, no repository is special, and it is
				818	trivial for another developer to take over maintenance of a
				819	project, either by mutual agreement, or because a maintainer
				820	becomes unresponsive or difficult to work with.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	821	</li><li class="listitem">
Junio C Hamano	ed7f4f6	2007-05-20 09:09:09	[diff] [blame]	822	The lack of a central group of "committers" means there is
				823	less need for formal decisions about who is "in" and who is
				824	"out".
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	825	</li></ul></div></div><div class="section" title="Allowing web browsing of a repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-gitweb"></a>Allowing web browsing of a repository</h3></div></div></div><p>The gitweb cgi script provides users an easy way to browse your
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	826	project's files and history without having to install git; see the file
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	827	gitweb/INSTALL in the git source tree for instructions on setting it up.</p></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-development-examples"></a>Examples</h2></div></div></div><div class="section" title="Maintaining topic branches for a Linux subsystem maintainer"><div class="titlepage"><div><div><h3 class="title"><a name="maintaining-topic-branches"></a>Maintaining topic branches for a Linux subsystem maintainer</h3></div></div></div><p>This describes how Tony Luck uses git in his role as maintainer of the
				828	IA64 architecture for the Linux kernel.</p><p>He uses two public branches:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	829	A "test" tree into which patches are initially placed so that they
				830	can get some exposure when integrated with other ongoing development.
				831	This tree is available to Andrew for pulling into -mm whenever he
				832	wants.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	833	</li><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	834	A "release" tree into which tested patches are moved for final sanity
				835	checking, and as a vehicle to send them upstream to Linus (by sending
				836	him a "please pull" request.)
				837	</li></ul></div><p>He also uses a set of temporary branches ("topic branches"), each
				838	containing a logical grouping of patches.</p><p>To set this up, first create your work tree by cloning Linus's public
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	839	tree:</p><div class="literallayout"><p>$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work<br>
				840	$ cd work</p></div><p>Linus's tree will be stored in the remote branch named origin/master,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	841	and can be updated using <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>; you can track other
				842	public trees using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a> to set up a "remote" and
				843	<a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> to keep them up-to-date; see
				844	<a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a>.</p><p>Now create the branches in which you are going to work; these start out
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	845	at the current tip of origin/master branch, and should be set up (using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	846	the —track option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>) to merge changes in from
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	847	Linus by default.</p><div class="literallayout"><p>$ git branch --track test origin/master<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	848	$ git branch --track release origin/master</p></div><p>These can be easily kept up to date using <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.</p><div class="literallayout"><p>$ git checkout test && git pull<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	849	$ git checkout release && git pull</p></div><p>Important note! If you have any local changes in these branches, then
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	850	this merge will create a commit object in the history (with no local
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	851	changes git will simply do a "fast-forward" merge). Many people dislike
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	852	the "noise" that this creates in the Linux history, so you should avoid
				853	doing this capriciously in the "release" branch, as these noisy commits
				854	will become part of the permanent history when you ask Linus to pull
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	855	from the release branch.</p><p>A few configuration variables (see <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>) can
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	856	make it easy to push both branches to your public tree. (See
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	857	<a class="xref" href="#setting-up-a-public-repository" title="Setting up a public repository">the section called “Setting up a public repository”</a>.)</p><div class="literallayout"><p>$ cat >> .git/config <<EOF<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	858	[remote "mytree"]<br>
				859	url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git<br>
				860	push = release<br>
				861	push = test<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	862	EOF</p></div><p>Then you can push both the test and release trees using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	863	<a class="ulink" href="git-push.html" target="_top">git-push(1)</a>:</p><div class="literallayout"><p>$ git push mytree</p></div><p>or push just one of the test and release branches using:</p><div class="literallayout"><p>$ git push mytree test</p></div><p>or</p><div class="literallayout"><p>$ git push mytree release</p></div><p>Now to apply some patches from the community. Think of a short
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	864	snappy name for a branch to hold this patch (or related group of
				865	patches), and create a new branch from the current tip of Linus's
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	866	branch:</p><div class="literallayout"><p>$ git checkout -b speed-up-spinlocks origin</p></div><p>Now you apply the patch(es), run some tests, and commit the change(s). If
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	867	the patch is a multi-part series, then you should apply each as a separate
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	868	commit to this branch.</p><div class="literallayout"><p>$ ... patch ... test ... commit [ ... patch ... test ... commit ]*</p></div><p>When you are happy with the state of this change, you can pull it into the
				869	"test" branch in preparation to make it public:</p><div class="literallayout"><p>$ git checkout test && git pull . speed-up-spinlocks</p></div><p>It is unlikely that you would have any conflicts here … but you might if you
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	870	spent a while on this step and had also pulled new versions from upstream.</p><p>Some time later when enough time has passed and testing done, you can pull the
				871	same branch into the "release" tree ready to go upstream. This is where you
				872	see the value of keeping each patch (or patch series) in its own branch. It
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	873	means that the patches can be moved into the "release" tree in any order.</p><div class="literallayout"><p>$ git checkout release && git pull . speed-up-spinlocks</p></div><p>After a while, you will have a number of branches, and despite the
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	874	well chosen names you picked for each of them, you may forget what
				875	they are for, or what status they are in. To get a reminder of what
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	876	changes are in a specific branch, use:</p><div class="literallayout"><p>$ git log linux..branchname \| git shortlog</p></div><p>To see whether it has already been merged into the test or release branches,
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	877	use:</p><div class="literallayout"><p>$ git log test..branchname</p></div><p>or</p><div class="literallayout"><p>$ git log release..branchname</p></div><p>(If this branch has not yet been merged, you will see some log entries.
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	878	If it has been merged, then there will be no output.)</p><p>Once a patch completes the great cycle (moving from test to release,
				879	then pulled by Linus, and finally coming back into your local
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	880	"origin/master" branch), the branch for this change is no longer needed.
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	881	You detect this when the output from:</p><div class="literallayout"><p>$ git log origin..branchname</p></div><p>is empty. At this point the branch can be deleted:</p><div class="literallayout"><p>$ git branch -d branchname</p></div><p>Some changes are so trivial that it is not necessary to create a separate
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	882	branch and then merge into each of the test and release branches. For
				883	these changes, just apply directly to the "release" branch, and then
				884	merge that into the "test" branch.</p><p>To create diffstat and shortlog summaries of changes to include in a "please
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	885	pull" request to Linus you can use:</p><div class="literallayout"><p>$ git diff --stat origin..release</p></div><p>and</p><div class="literallayout"><p>$ git log -p origin..release \| git shortlog</p></div><p>Here are some of the scripts that simplify all this even further.</p><div class="literallayout"><p>==== update script ====<br>
				886	# Update a branch in my GIT tree. If the branch to be updated<br>
				887	# is origin, then pull from kernel.org. Otherwise merge<br>
				888	# origin/master branch into test\|release branch<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	889	<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	890	case "$1" in<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	891	test\|release)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	892	git checkout $1 && git pull . origin<br>
				893	;;<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	894	origin)<br>
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	895	before=$(git rev-parse refs/remotes/origin/master)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	896	git fetch origin<br>
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	897	after=$(git rev-parse refs/remotes/origin/master)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	898	if [ $before != $after ]<br>
				899	then<br>
				900	git log $before..$after \| git shortlog<br>
				901	fi<br>
				902	;;<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	903	*)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	904	echo "Usage: $0 origin\|test\|release" 1>&2<br>
				905	exit 1<br>
				906	;;<br>
				907	esac</p></div><div class="literallayout"><p>==== merge script ====<br>
				908	# Merge a branch into either the test or release branch<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	909	<br>
				910	pname=$0<br>
				911	<br>
				912	usage()<br>
				913	{<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	914	echo "Usage: $pname branch test\|release" 1>&2<br>
				915	exit 1<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	916	}<br>
				917	<br>
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	918	git show-ref -q --verify -- refs/heads/"$1" \|\| {<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	919	echo "Can't see branch <$1>" 1>&2<br>
				920	usage<br>
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	921	}<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	922	<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	923	case "$2" in<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	924	test\|release)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	925	if [ $(git log $2..$1 \| wc -c) -eq 0 ]<br>
				926	then<br>
				927	echo $1 already merged into $2 1>&2<br>
				928	exit 1<br>
				929	fi<br>
				930	git checkout $2 && git pull . $1<br>
				931	;;<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	932	*)<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	933	usage<br>
				934	;;<br>
				935	esac</p></div><div class="literallayout"><p>==== status script ====<br>
				936	# report on status of my ia64 GIT tree<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	937	<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	938	gb=$(tput setab 2)<br>
				939	rb=$(tput setab 1)<br>
				940	restore=$(tput setab 9)<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	941	<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	942	if [ `git rev-list test..release \| wc -c` -gt 0 ]<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	943	then<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	944	echo $rb Warning: commits in release that are not in test $restore<br>
				945	git log test..release<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	946	fi<br>
				947	<br>
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	948	for branch in `git show-ref --heads \| sed 's\|^.*/\|\|'`<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	949	do<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	950	if [ $branch = test -o $branch = release ]<br>
				951	then<br>
				952	continue<br>
				953	fi<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	954	<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	955	echo -n $gb ======= $branch ====== $restore " "<br>
				956	status=<br>
				957	for ref in test release origin/master<br>
				958	do<br>
				959	if [ `git rev-list $ref..$branch \| wc -c` -gt 0 ]<br>
				960	then<br>
				961	status=$status${ref:0:1}<br>
				962	fi<br>
				963	done<br>
				964	case $status in<br>
				965	trl)<br>
				966	echo $rb Need to pull into test $restore<br>
				967	;;<br>
				968	rl)<br>
				969	echo "In test"<br>
				970	;;<br>
				971	l)<br>
				972	echo "Waiting for linus"<br>
				973	;;<br>
				974	"")<br>
				975	echo $rb All done $restore<br>
				976	;;<br>
				977	*)<br>
				978	echo $rb "<$status>" $restore<br>
				979	;;<br>
				980	esac<br>
				981	git log origin/master..$branch \| git shortlog<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	982	done</p></div></div></div></div><div class="chapter" title="Chapter 5. Rewriting history and maintaining patch series"><div class="titlepage"><div><div><h2 class="title"><a name="cleaning-up-history"></a>Chapter 5. Rewriting history and maintaining patch series</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></div><p>Normally commits are only added to a project, never taken away or
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	983	replaced. Git is designed with this assumption, and violating it will
				984	cause git's merge machinery (for example) to do the wrong thing.</p><p>However, there is a situation in which it can be useful to violate this
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	985	assumption.</p><div class="section" title="Creating the perfect patch series"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series"></a>Creating the perfect patch series</h2></div></div></div><p>Suppose you are a contributor to a large project, and you want to add a
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	986	complicated feature, and to present it to the other developers in a way
				987	that makes it easy for them to read your changes, verify that they are
				988	correct, and understand why you made each change.</p><p>If you present all of your changes as a single patch (or commit), they
Junio C Hamano	db911ee	2007-02-28 08:13:52	[diff] [blame]	989	may find that it is too much to digest all at once.</p><p>If you present them with the entire history of your work, complete with
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	990	mistakes, corrections, and dead ends, they may be overwhelmed.</p><p>So the ideal is usually to produce a series of patches such that:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	991	Each patch can be applied in order.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	992	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	993	Each patch includes a single logical change, together with a
				994	message explaining the change.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	995	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	996	No patch introduces a regression: after applying any initial
				997	part of the series, the resulting project still compiles and
				998	works, and has no bugs that it didn't have before.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	999	</li><li class="listitem">
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1000	The complete series produces the same end result as your own
				1001	(probably much messier!) development process did.
				1002	</li></ol></div><p>We will introduce some tools that can help you do this, explain how to
				1003	use them, and then explain some of the problems that can arise because
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1004	you are rewriting history.</p></div><div class="section" title="Keeping a patch series up to date using git rebase"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-git-rebase"></a>Keeping a patch series up to date using git rebase</h2></div></div></div><p>Suppose that you create a branch "mywork" on a remote-tracking branch
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1005	"origin", and create some commits on top of it:</p><div class="literallayout"><p>$ git checkout -b mywork origin<br>
				1006	$ vi file.txt<br>
				1007	$ git commit<br>
				1008	$ vi otherfile.txt<br>
				1009	$ git commit<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1010	...</p></div><p>You have performed no merges into mywork, so it is just a simple linear
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	1011	sequence of patches on top of "origin":</p><pre class="literallayout"> o--o--o <-- origin
				1012	\
				1013	o--o--o <-- mywork</pre><p>Some more interesting work has been done in the upstream project, and
				1014	"origin" has advanced:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
				1015	\
				1016	a--b--c <-- mywork</pre><p>At this point, you could use "pull" to merge your changes back in;
				1017	the result would create a new merge commit, like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
				1018	\ \
				1019	a--b--c--m <-- mywork</pre><p>However, if you prefer to keep the history in mywork a simple series of
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1020	commits without any merges, you may instead choose to use
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1021	<a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a>:</p><div class="literallayout"><p>$ git checkout mywork<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1022	$ git rebase origin</p></div><p>This will remove each of your commits from mywork, temporarily saving
Junio C Hamano	0868a30	2008-07-22 09:20:44	[diff] [blame]	1023	them as patches (in a directory named ".git/rebase-apply"), update mywork to
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1024	point at the latest version of origin, then apply each of the saved
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	1025	patches to the new mywork. The result will look like:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
				1026	\
				1027	a'--b'--c' <-- mywork</pre><p>In the process, it may discover conflicts. In that case it will stop
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1028	and allow you to fix the conflicts; after fixing conflicts, use <code class="literal">git add</code>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1029	to update the index with those contents, and then, instead of
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1030	running <code class="literal">git commit</code>, just run</p><div class="literallayout"><p>$ git rebase --continue</p></div><p>and git will continue applying the rest of the patches.</p><p>At any point you may use the <code class="literal">—abort</code> option to abort this process and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1031	return mywork to the state it had before you started the rebase:</p><div class="literallayout"><p>$ git rebase --abort</p></div></div><div class="section" title="Rewriting a single commit"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="rewriting-one-commit"></a>Rewriting a single commit</h2></div></div></div><p>We saw in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a> that you can replace the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1032	most recent commit using</p><div class="literallayout"><p>$ git commit --amend</p></div><p>which will replace the old commit by a new commit incorporating your
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1033	changes, giving you a chance to edit the old commit message first.</p><p>You can also use a combination of this and <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a> to
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1034	replace a commit further back in your history and recreate the
				1035	intervening changes on top of it. First, tag the problematic commit
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1036	with</p><div class="literallayout"><p>$ git tag bad mywork~5</p></div><p>(Either gitk or <code class="literal">git log</code> may be useful for finding the commit.)</p><p>Then check out that commit, edit it, and rebase the rest of the series
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	1037	on top of it (note that we could check out the commit on a temporary
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1038	branch, but instead we're using a <a class="link" href="#detached-head" title="Examining an old version without creating a new branch">detached head</a>):</p><div class="literallayout"><p>$ git checkout bad<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1039	$ # make changes here and update the index<br>
				1040	$ git commit --amend<br>
				1041	$ git rebase --onto HEAD bad mywork</p></div><p>When you're done, you'll be left with mywork checked out, with the top
Junio C Hamano	0e3cb53	2007-04-17 08:28:11	[diff] [blame]	1042	patches on mywork reapplied on top of your modified commit. You can
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1043	then clean up with</p><div class="literallayout"><p>$ git tag -d bad</p></div><p>Note that the immutable nature of git history means that you haven't really
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	1044	"modified" existing commits; instead, you have replaced the old commits with
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1045	new commits having new object names.</p></div><div class="section" title="Reordering or selecting from a patch series"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="reordering-patch-series"></a>Reordering or selecting from a patch series</h2></div></div></div><p>Given one existing commit, the <a class="ulink" href="git-cherry-pick.html" target="_top">git-cherry-pick(1)</a> command
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1046	allows you to apply the change introduced by that commit and create a
				1047	new commit that records it. So, for example, if "mywork" points to a
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1048	series of patches on top of "origin", you might do something like:</p><div class="literallayout"><p>$ git checkout -b mywork-new origin<br>
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1049	$ gitk origin..mywork &</p></div><p>and browse through the list of patches in the mywork branch using gitk,
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1050	applying them (possibly in a different order) to mywork-new using
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1051	cherry-pick, and possibly modifying them as you go using <code class="literal">git commit —amend</code>.
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1052	The <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> command may also help as it allows you to
Junio C Hamano	8b8b0f2	2007-08-26 22:10:26	[diff] [blame]	1053	individually select diff hunks for inclusion in the index (by
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1054	right-clicking on the diff hunk and choosing "Stage Hunk for Commit").</p><p>Another technique is to use <code class="literal">git format-patch</code> to create a series of
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1055	patches, then reset the state to before the patches:</p><div class="literallayout"><p>$ git format-patch origin<br>
				1056	$ git reset --hard origin</p></div><p>Then modify, reorder, or eliminate patches as preferred before applying
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1057	them again with <a class="ulink" href="git-am.html" target="_top">git-am(1)</a>.</p></div><div class="section" title="Other tools"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series-tools"></a>Other tools</h2></div></div></div><p>There are numerous other tools, such as StGit, which exist for the
Junio C Hamano	db911ee	2007-02-28 08:13:52	[diff] [blame]	1058	purpose of maintaining a patch series. These are outside of the scope of
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1059	this manual.</p></div><div class="section" title="Problems with rewriting history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="problems-With-rewriting-history"></a>Problems with rewriting history</h2></div></div></div><p>The primary problem with rewriting the history of a branch has to do
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1060	with merging. Suppose somebody fetches your branch and merges it into
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	1061	their branch, with a result something like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
				1062	\ \
				1063	t--t--t--m <-- their branch:</pre><p>Then suppose you modify the last three commits:</p><pre class="literallayout"> o--o--o <-- new head of origin
				1064	/
				1065	o--o--O--o--o--o <-- old head of origin</pre><p>If we examined all this history together in one repository, it will
				1066	look like:</p><pre class="literallayout"> o--o--o <-- new head of origin
				1067	/
				1068	o--o--O--o--o--o <-- old head of origin
				1069	\ \
				1070	t--t--t--m <-- their branch:</pre><p>Git has no way of knowing that the new head is an updated version of
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1071	the old head; it treats this situation exactly the same as it would if
				1072	two developers had independently done the work on the old and new heads
				1073	in parallel. At this point, if someone attempts to merge the new head
				1074	in to their branch, git will attempt to merge together the two (old and
				1075	new) lines of development, instead of trying to replace the old by the
				1076	new. The results are likely to be unexpected.</p><p>You may still choose to publish branches whose history is rewritten,
				1077	and it may be useful for others to be able to fetch those branches in
				1078	order to examine or test them, but they should not attempt to pull such
				1079	branches into their own work.</p><p>For true distributed development that supports proper merging,
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1080	published branches should never be rewritten.</p></div><div class="section" title="Why bisecting merge commits can be harder than bisecting linear history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="bisect-merges"></a>Why bisecting merge commits can be harder than bisecting linear history</h2></div></div></div><p>The <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command correctly handles history that
Junio C Hamano	393e57f	2007-11-20 04:53:25	[diff] [blame]	1081	includes merge commits. However, when the commit that it finds is a
				1082	merge commit, the user may need to work harder than usual to figure out
				1083	why that commit introduced a problem.</p><p>Imagine this history:</p><pre class="literallayout"> ---Z---o---X---...---o---A---C---D
				1084	\ /
				1085	o---o---Y---...---o---B</pre><p>Suppose that on the upper line of development, the meaning of one
				1086	of the functions that exists at Z is changed at commit X. The
				1087	commits from Z leading to A change both the function's
				1088	implementation and all calling sites that exist at Z, as well
				1089	as new calling sites they add, to be consistent. There is no
				1090	bug at A.</p><p>Suppose that in the meantime on the lower line of development somebody
				1091	adds a new calling site for that function at commit Y. The
				1092	commits from Z leading to B all assume the old semantics of that
				1093	function and the callers and the callee are consistent with each
				1094	other. There is no bug at B, either.</p><p>Suppose further that the two development lines merge cleanly at C,
				1095	so no conflict resolution is required.</p><p>Nevertheless, the code at C is broken, because the callers added
				1096	on the lower line of development have not been converted to the new
				1097	semantics introduced on the upper line of development. So if all
				1098	you know is that D is bad, that Z is good, and that
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1099	<a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> identifies C as the culprit, how will you
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1100	figure out that the problem is due to this change in semantics?</p><p>When the result of a <code class="literal">git bisect</code> is a non-merge commit, you should
Junio C Hamano	393e57f	2007-11-20 04:53:25	[diff] [blame]	1101	normally be able to discover the problem by examining just that commit.
				1102	Developers can make this easy by breaking their changes into small
				1103	self-contained commits. That won't help in the case above, however,
				1104	because the problem isn't obvious from examination of any single
				1105	commit; instead, a global view of the development is required. To
				1106	make matters worse, the change in semantics in the problematic
				1107	function may be just one small part of the changes in the upper
				1108	line of development.</p><p>On the other hand, if instead of merging at C you had rebased the
				1109	history between Z to B on top of A, you would have gotten this
				1110	linear history:</p><pre class="literallayout"> ---Z---o---X--...---o---A---o---o---Y--...---o---B--D</pre><p>Bisecting between Z and D would hit a single culprit commit Y*,
				1111	and understanding why Y* was broken would probably be easier.</p><p>Partly for this reason, many experienced git users, even when
				1112	working on an otherwise merge-heavy project, keep the history
				1113	linear by rebasing against the latest upstream version before
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1114	publishing.</p></div></div><div class="chapter" title="Chapter 6. Advanced branch management"><div class="titlepage"><div><div><h2 class="title"><a name="advanced-branch-management"></a>Chapter 6. Advanced branch management</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote branches</a></span></dt></dl></div><div class="section" title="Fetching individual branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-individual-branches"></a>Fetching individual branches</h2></div></div></div><p>Instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1115	to update one branch at a time, and to store it locally under an
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1116	arbitrary name:</p><div class="literallayout"><p>$ git fetch origin todo:my-todo-work</p></div><p>The first argument, "origin", just tells git to fetch from the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1117	repository you originally cloned from. The second argument tells git
				1118	to fetch the branch named "todo" from the remote repository, and to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1119	store it locally under the name refs/heads/my-todo-work.</p><p>You can also fetch branches from other repositories; so</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:example-master</p></div><p>will create a new branch named "example-master" and store in it the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1120	branch named "master" from the repository at the given URL. If you
				1121	already have a branch named example-master, it will attempt to
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1122	<a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> to the commit given by example.com's
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1123	master branch. In more detail:</p></div><div class="section" title="git fetch and fast-forwards"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetch-fast-forwards"></a>git fetch and fast-forwards</h2></div></div></div><p>In the previous example, when updating an existing branch, "git fetch"
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1124	checks to make sure that the most recent commit on the remote
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1125	branch is a descendant of the most recent commit on your copy of the
				1126	branch before updating your copy of the branch to point at the new
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	1127	commit. Git calls this process a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>.</p><p>A fast-forward looks something like this:</p><pre class="literallayout"> o--o--o--o <-- old head of the branch
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	1128	\
				1129	o--o--o <-- new head of the branch</pre><p>In some cases it is possible that the new head will <span class="strong"><strong>not</strong></span> actually be
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1130	a descendant of the old head. For example, the developer may have
				1131	realized she made a serious mistake, and decided to backtrack,
Junio C Hamano	c51fede	2007-03-12 07:29:20	[diff] [blame]	1132	resulting in a situation like:</p><pre class="literallayout"> o--o--o--o--a--b <-- old head of the branch
				1133	\
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1134	o--o--o <-- new head of the branch</pre><p>In this case, "git fetch" will fail, and print out a warning.</p><p>In that case, you can still force git to update to the new head, as
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1135	described in the following section. However, note that in the
				1136	situation above this may mean losing the commits labeled "a" and "b",
				1137	unless you've already created a reference of your own pointing to
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1138	them.</p></div><div class="section" title="Forcing git fetch to do non-fast-forward updates"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="forcing-fetch"></a>Forcing git fetch to do non-fast-forward updates</h2></div></div></div><p>If git fetch fails because the new head of a branch is not a
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1139	descendant of the old head, you may force the update with:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git +master:refs/remotes/example/master</p></div><p>Note the addition of the "+" sign. Alternatively, you can use the "-f"
				1140	flag to force updates of all the fetched branches, as in:</p><div class="literallayout"><p>$ git fetch -f origin</p></div><p>Be aware that commits that the old version of example/master pointed at
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1141	may be lost, as we saw in the previous section.</p></div><div class="section" title="Configuring remote branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="remote-branch-configuration"></a>Configuring remote branches</h2></div></div></div><p>We saw above that "origin" is just a shortcut to refer to the
Junio C Hamano	db911ee	2007-02-28 08:13:52	[diff] [blame]	1142	repository that you originally cloned from. This information is
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1143	stored in git configuration variables, which you can see using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1144	<a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p><div class="literallayout"><p>$ git config -l<br>
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1145	core.repositoryformatversion=0<br>
				1146	core.filemode=true<br>
				1147	core.logallrefupdates=true<br>
				1148	remote.origin.url=git://git.kernel.org/pub/scm/git/git.git<br>
				1149	remote.origin.fetch=+refs/heads/:refs/remotes/origin/<br>
				1150	branch.master.remote=origin<br>
				1151	branch.master.merge=refs/heads/master</p></div><p>If there are other repositories that you also use frequently, you can
				1152	create similar configuration options to save typing; for example,
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1153	after</p><div class="literallayout"><p>$ git config remote.example.url git://example.com/proj.git</p></div><p>then the following two commands will do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:refs/remotes/example/master<br>
				1154	$ git fetch example master:refs/remotes/example/master</p></div><p>Even better, if you add one more option:</p><div class="literallayout"><p>$ git config remote.example.fetch master:refs/remotes/example/master</p></div><p>then the following commands will all do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:refs/remotes/example/master<br>
				1155	$ git fetch example master:refs/remotes/example/master<br>
Junio C Hamano	1d36888	2008-08-11 22:03:10	[diff] [blame]	1156	$ git fetch example</p></div><p>You can also add a "+" to force the update each time:</p><div class="literallayout"><p>$ git config remote.example.fetch +master:ref/remotes/example/master</p></div><p>Don't do this unless you're sure you won't mind "git fetch" possibly
				1157	throwing away commits on <span class="emphasis"><em>example/master</em></span>.</p><p>Also note that all of the above configuration can be performed by
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1158	directly editing the file .git/config instead of using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1159	<a class="ulink" href="git-config.html" target="_top">git-config(1)</a>.</p><p>See <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1160	options mentioned above.</p></div></div><div class="chapter" title="Chapter 7. Git concepts"><div class="titlepage"><div><div><h2 class="title"><a name="git-concepts"></a>Chapter 7. Git concepts</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></div><p>Git is built on a small number of simple but powerful ideas. While it
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1161	is possible to get things done without understanding them, you will find
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1162	git much more intuitive if you do.</p><p>We start with the most important, the <a class="link" href="#def_object_database">object database</a> and the <a class="link" href="#def_index">index</a>.</p><div class="section" title="The Object Database"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-object-database"></a>The Object Database</h2></div></div></div><p>We already saw in <a class="xref" href="#understanding-commits" title="Understanding History: Commits">the section called “Understanding History: Commits”</a> that all commits are stored
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1163	under a 40-digit "object name". In fact, all the information needed to
				1164	represent the history of a project is stored in objects with such names.
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1165	In each case the name is calculated by taking the SHA-1 hash of the
				1166	contents of the object. The SHA-1 hash is a cryptographic hash function.
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1167	What that means to us is that it is impossible to find two different
				1168	objects with the same name. This has a number of advantages; among
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1169	others:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1170	Git can quickly determine whether two objects are identical or not,
				1171	just by comparing names.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1172	</li><li class="listitem">
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1173	Since object names are computed the same way in every repository, the
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1174	same content stored in two repositories will always be stored under
				1175	the same name.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1176	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1177	Git can detect errors when it reads an object, by checking that the
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1178	object's name is still the SHA-1 hash of its contents.
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1179	</li></ul></div><p>(See <a class="xref" href="#object-details" title="Object storage format">the section called “Object storage format”</a> for the details of the object formatting and
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1180	SHA-1 calculation.)</p><p>There are four different types of objects: "blob", "tree", "commit", and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1181	"tag".</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1182	A <a class="link" href="#def_blob_object">"blob" object</a> is used to store file data.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1183	</li><li class="listitem">
Junio C Hamano	d32738e	2008-07-09 19:53:42	[diff] [blame]	1184	A <a class="link" href="#def_tree_object">"tree" object</a> ties one or more
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1185	"blob" objects into a directory structure. In addition, a tree object
				1186	can refer to other tree objects, thus creating a directory hierarchy.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1187	</li><li class="listitem">
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1188	A <a class="link" href="#def_commit_object">"commit" object</a> ties such directory hierarchies
				1189	together into a <a class="link" href="#def_DAG">directed acyclic graph</a> of revisions—each
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1190	commit contains the object name of exactly one tree designating the
				1191	directory hierarchy at the time of the commit. In addition, a commit
				1192	refers to "parent" commit objects that describe the history of how we
				1193	arrived at that directory hierarchy.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1194	</li><li class="listitem">
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1195	A <a class="link" href="#def_tag_object">"tag" object</a> symbolically identifies and can be
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1196	used to sign other objects. It contains the object name and type of
				1197	another object, a symbolic name (of course!) and, optionally, a
				1198	signature.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1199	</li></ul></div><p>The object types in some more detail:</p><div class="section" title="Commit Object"><div class="titlepage"><div><div><h3 class="title"><a name="commit-object"></a>Commit Object</h3></div></div></div><p>The "commit" object links a physical state of a tree with a description
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1200	of how we got there and why. Use the —pretty=raw option to
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1201	<a class="ulink" href="git-show.html" target="_top">git-show(1)</a> or <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> to examine your favorite
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1202	commit:</p><div class="literallayout"><p>$ git show -s --pretty=raw 2be7fcb476<br>
				1203	commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4<br>
				1204	tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf<br>
				1205	parent 257a84d9d02e90447b149af58b271c19405edb6a<br>
				1206	author Dave Watson <dwatson@mimvista.com> 1187576872 -0400<br>
				1207	committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700<br>
				1208	<br>
				1209	Fix misspelling of 'suppress' in docs<br>
				1210	<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1211	Signed-off-by: Junio C Hamano <gitster@pobox.com></p></div><p>As you can see, a commit is defined by:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1212	a tree: The SHA-1 name of a tree object (as defined below), representing
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1213	the contents of a directory at a certain point in time.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1214	</li><li class="listitem">
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1215	parent(s): The SHA-1 name of some number of commits which represent the
Junio C Hamano	878cc1e	2007-12-14 08:35:13	[diff] [blame]	1216	immediately previous step(s) in the history of the project. The
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1217	example above has one parent; merge commits may have more than
				1218	one. A commit with no parents is called a "root" commit, and
				1219	represents the initial revision of a project. Each project must have
				1220	at least one root. A project can also have multiple roots, though
				1221	that isn't common (or necessarily a good idea).
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1222	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1223	an author: The name of the person responsible for this change, together
				1224	with its date.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1225	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1226	a committer: The name of the person who actually created the commit,
				1227	with the date it was done. This may be different from the author, for
				1228	example, if the author was someone who wrote a patch and emailed it
				1229	to the person who used it to create the commit.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1230	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1231	a comment describing this commit.
				1232	</li></ul></div><p>Note that a commit does not itself contain any information about what
				1233	actually changed; all changes are calculated by comparing the contents
				1234	of the tree referred to by this commit with the trees associated with
				1235	its parents. In particular, git does not attempt to record file renames
				1236	explicitly, though it can identify cases where the existence of the same
				1237	file data at changing paths suggests a rename. (See, for example, the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1238	-M option to <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>).</p><p>A commit is usually created by <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>, which creates a
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1239	commit whose parent is normally the current HEAD, and whose tree is
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1240	taken from the content currently stored in the index.</p></div><div class="section" title="Tree Object"><div class="titlepage"><div><div><h3 class="title"><a name="tree-object"></a>Tree Object</h3></div></div></div><p>The ever-versatile <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command can also be used to
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1241	examine tree objects, but <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a> will give you more
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1242	details:</p><div class="literallayout"><p>$ git ls-tree fb3a8bdd0ce<br>
				1243	100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore<br>
				1244	100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap<br>
				1245	100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING<br>
				1246	040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation<br>
				1247	100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN<br>
				1248	100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL<br>
				1249	100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile<br>
				1250	100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README<br>
				1251	...</p></div><p>As you can see, a tree object contains a list of entries, each with a
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1252	mode, object type, SHA-1 name, and name, sorted by name. It represents
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1253	the contents of a single directory tree.</p><p>The object type may be a blob, representing the contents of a file, or
				1254	another tree, representing the contents of a subdirectory. Since trees
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1255	and blobs, like all other objects, are named by the SHA-1 hash of their
				1256	contents, two trees have the same SHA-1 name if and only if their
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1257	contents (including, recursively, the contents of all subdirectories)
				1258	are identical. This allows git to quickly determine the differences
				1259	between two related tree objects, since it can ignore any entries with
				1260	identical object names.</p><p>(Note: in the presence of submodules, trees may also have commits as
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1261	entries. See <a class="xref" href="#submodules" title="Chapter 8. Submodules">Chapter 8, <i>Submodules</i></a> for documentation.)</p><p>Note that the files all have mode 644 or 755: git actually only pays
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1262	attention to the executable bit.</p></div><div class="section" title="Blob Object"><div class="titlepage"><div><div><h3 class="title"><a name="blob-object"></a>Blob Object</h3></div></div></div><p>You can use <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> to examine the contents of a blob; take,
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1263	for example, the blob in the entry for "COPYING" from the tree above:</p><div class="literallayout"><p>$ git show 6ff87c4664<br>
				1264	<br>
				1265	Note that the only valid version of the GPL as far as this project<br>
				1266	is concerned is _this_ particular version of the license (ie v2, not<br>
				1267	v2.2 or v3.x or whatever), unless explicitly otherwise stated.<br>
				1268	...</p></div><p>A "blob" object is nothing but a binary blob of data. It doesn't refer
				1269	to anything else or have attributes of any kind.</p><p>Since the blob is entirely defined by its data, if two files in a
				1270	directory tree (or in multiple different versions of the repository)
				1271	have the same contents, they will share the same blob object. The object
				1272	is totally independent of its location in the directory tree, and
				1273	renaming a file does not change the object that file is associated with.</p><p>Note that any tree or blob object can be examined using
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1274	<a class="ulink" href="git-show.html" target="_top">git-show(1)</a> with the <revision>:<path> syntax. This can
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1275	sometimes be useful for browsing the contents of a tree that is not
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1276	currently checked out.</p></div><div class="section" title="Trust"><div class="titlepage"><div><div><h3 class="title"><a name="trust"></a>Trust</h3></div></div></div><p>If you receive the SHA-1 name of a blob from one source, and its contents
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1277	from another (possibly untrusted) source, you can still trust that those
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1278	contents are correct as long as the SHA-1 name agrees. This is because
				1279	the SHA-1 is designed so that it is infeasible to find different contents
				1280	that produce the same hash.</p><p>Similarly, you need only trust the SHA-1 name of a top-level tree object
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1281	to trust the contents of the entire directory that it refers to, and if
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1282	you receive the SHA-1 name of a commit from a trusted source, then you
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1283	can easily verify the entire history of commits reachable through
				1284	parents of that commit, and all of those contents of the trees referred
				1285	to by those commits.</p><p>So to introduce some real trust in the system, the only thing you need
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1286	to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the
				1287	name of a top-level commit. Your digital signature shows others
				1288	that you trust that commit, and the immutability of the history of
				1289	commits tells others that they can trust the whole history.</p><p>In other words, you can easily validate a whole archive by just
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1290	sending out a single email that tells the people the name (SHA-1 hash)
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1291	of the top commit, and digitally sign that email using something
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1292	like GPG/PGP.</p><p>To assist in this, git also provides the tag object…</p></div><div class="section" title="Tag Object"><div class="titlepage"><div><div><h3 class="title"><a name="tag-object"></a>Tag Object</h3></div></div></div><p>A tag object contains an object, object type, tag name, the name of the
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1293	person ("tagger") who created the tag, and a message, which may contain
Junio C Hamano	d32738e	2008-07-09 19:53:42	[diff] [blame]	1294	a signature, as can be seen using <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a>:</p><div class="literallayout"><p>$ git cat-file tag v1.5.0<br>
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1295	object 437b1b20df4b356c9342dac8d38849f24ef44f27<br>
				1296	type commit<br>
				1297	tag v1.5.0<br>
				1298	tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000<br>
				1299	<br>
				1300	GIT 1.5.0<br>
				1301	-----BEGIN PGP SIGNATURE-----<br>
				1302	Version: GnuPG v1.4.6 (GNU/Linux)<br>
				1303	<br>
				1304	iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui<br>
				1305	nLE/L9aUXdWeTFPron96DLA=<br>
				1306	=2E+0<br>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1307	-----END PGP SIGNATURE-----</p></div><p>See the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command to learn how to create and verify tag
				1308	objects. (Note that <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> can also be used to create
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1309	"lightweight tags", which are not tag objects at all, but just simple
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1310	references whose names begin with "refs/tags/").</p></div><div class="section" title="How git stores objects efficiently: pack files"><div class="titlepage"><div><div><h3 class="title"><a name="pack-files"></a>How git stores objects efficiently: pack files</h3></div></div></div><p>Newly created objects are initially created in a file named after the
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1311	object's SHA-1 hash (stored in .git/objects).</p><p>Unfortunately this system becomes inefficient once a project has a
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1312	lot of objects. Try this on an old project:</p><div class="literallayout"><p>$ git count-objects<br>
				1313	6930 objects, 47620 kilobytes</p></div><p>The first number is the number of objects which are kept in
				1314	individual files. The second is the amount of space taken up by
				1315	those "loose" objects.</p><p>You can save space and make git faster by moving these loose objects in
				1316	to a "pack file", which stores a group of objects in an efficient
				1317	compressed format; the details of how pack files are formatted can be
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1318	found in <a class="ulink" href="technical/pack-format.txt" target="_top">technical/pack-format.txt</a>.</p><p>To put the loose objects into a pack, just run git repack:</p><div class="literallayout"><p>$ git repack<br>
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1319	Generating pack...<br>
				1320	Done counting 6020 objects.<br>
				1321	Deltifying 6020 objects.<br>
				1322	100% (6020/6020) done<br>
				1323	Writing 6020 objects.<br>
				1324	100% (6020/6020) done<br>
				1325	Total 6020, written 6020 (delta 4070), reused 0 (delta 0)<br>
				1326	Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.</p></div><p>You can then run</p><div class="literallayout"><p>$ git prune</p></div><p>to remove any of the "loose" objects that are now contained in the
				1327	pack. This will also remove any unreferenced objects (which may be
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1328	created when, for example, you use "git reset" to remove a commit).
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1329	You can verify that the loose objects are gone by looking at the
				1330	.git/objects directory or by running</p><div class="literallayout"><p>$ git count-objects<br>
				1331	0 objects, 0 kilobytes</p></div><p>Although the object files are gone, any commands that refer to those
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1332	objects will work exactly as they did before.</p><p>The <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1333	you, so is normally the only high-level command you need.</p></div><div class="section" title="Dangling objects"><div class="titlepage"><div><div><h3 class="title"><a name="dangling-objects"></a>Dangling objects</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1334	objects. They are not a problem.</p><p>The most common cause of dangling objects is that you've rebased a
				1335	branch, or you have pulled from somebody else who rebased a branch—see
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1336	<a class="xref" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">Chapter 5, <i>Rewriting history and maintaining patch series</i></a>. In that case, the old head of the original
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1337	branch still exists, as does everything it pointed to. The branch
				1338	pointer itself just doesn't, since you replaced it with another one.</p><p>There are also other situations that cause dangling objects. For
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1339	example, a "dangling blob" may arise because you did a "git add" of a
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1340	file, but then, before you actually committed it and made it part of the
				1341	bigger picture, you changed something else in that file and committed
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1342	that <span class="strong"><strong>updated</strong></span> thing—the old state that you added originally ends up
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1343	not being pointed to by any commit or tree, so it's now a dangling blob
				1344	object.</p><p>Similarly, when the "recursive" merge strategy runs, and finds that
				1345	there are criss-cross merges and thus more than one merge base (which is
				1346	fairly unusual, but it does happen), it will generate one temporary
				1347	midway tree (or possibly even more, if you had lots of criss-crossing
				1348	merges and more than two merge bases) as a temporary internal merge
				1349	base, and again, those are real objects, but the end result will not end
				1350	up pointing to them, so they end up "dangling" in your repository.</p><p>Generally, dangling objects aren't anything to worry about. They can
				1351	even be very useful: if you screw something up, the dangling objects can
				1352	be how you recover your old tree (say, you did a rebase, and realized
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1353	that you really didn't want to—you can look at what dangling objects
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1354	you have, and decide to reset your head to some old dangling state).</p><p>For commits, you can just use:</p><div class="literallayout"><p>$ gitk <dangling-commit-sha-goes-here> --not --all</p></div><p>This asks for all the history reachable from the given commit but not
				1355	from any branch, tag, or other reference. If you decide it's something
				1356	you want, you can always create a new reference to it, e.g.,</p><div class="literallayout"><p>$ git branch recovered-branch <dangling-commit-sha-goes-here></p></div><p>For blobs and trees, you can't do the same, but you can still examine
				1357	them. You can just do</p><div class="literallayout"><p>$ git show <dangling-blob/tree-sha-goes-here></p></div><p>to show what the contents of the blob were (or, for a tree, basically
				1358	what the "ls" for that directory was), and that may give you some idea
				1359	of what the operation was that left that dangling object.</p><p>Usually, dangling blobs and trees aren't very interesting. They're
				1360	almost always the result of either being a half-way mergebase (the blob
				1361	will often even have the conflict markers from a merge in it, if you
				1362	have had conflicting merges that you fixed up by hand), or simply
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1363	because you interrupted a "git fetch" with ^C or something like that,
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1364	leaving _some_ of the new objects in the object database, but just
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1365	dangling and useless.</p><p>Anyway, once you are sure that you're not interested in any dangling
				1366	state, you can just prune all unreachable objects:</p><div class="literallayout"><p>$ git prune</p></div><p>and they'll be gone. But you should only run "git prune" on a quiescent
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1367	repository—it's kind of like doing a filesystem fsck recovery: you
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1368	don't want to do that while the filesystem is mounted.</p><p>(The same is true of "git fsck" itself, btw, but since
				1369	<code class="literal">git fsck</code> never actually <span class="strong"><strong>changes</strong></span> the repository, it just reports
				1370	on what it found, <code class="literal">git fsck</code> itself is never <span class="emphasis"><em>dangerous</em></span> to run.
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1371	Running it while somebody is actually changing the repository can cause
				1372	confusing and scary messages, but it won't actually do anything bad. In
				1373	contrast, running "git prune" while somebody is actively changing the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1374	repository is a <span class="strong"><strong>BAD</strong></span> idea).</p></div><div class="section" title="Recovering from repository corruption"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-from-repository-corruption"></a>Recovering from repository corruption</h3></div></div></div><p>By design, git treats data trusted to it with caution. However, even in
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1375	the absence of bugs in git itself, it is still possible that hardware or
				1376	operating system errors could corrupt data.</p><p>The first defense against such problems is backups. You can back up a
				1377	git directory using clone, or just using cp, tar, or any other backup
				1378	mechanism.</p><p>As a last resort, you can search for the corrupted objects and attempt
				1379	to replace them by hand. Back up your repository before attempting this
				1380	in case you corrupt things even more in the process.</p><p>We'll assume that the problem is a single missing or corrupted blob,
Junio C Hamano	878cc1e	2007-12-14 08:35:13	[diff] [blame]	1381	which is sometimes a solvable problem. (Recovering missing trees and
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1382	especially commits is <span class="strong"><strong>much</strong></span> harder).</p><p>Before starting, verify that there is corruption, and figure out where
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1383	it is with <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a>; this may be time-consuming.</p><p>Assume the output looks like this:</p><div class="literallayout"><p>$ git fsck --full<br>
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1384	broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8<br>
				1385	to blob 4b9458b3786228369c63936db65827de3cc06200<br>
				1386	missing blob 4b9458b3786228369c63936db65827de3cc06200</p></div><p>(Typically there will be some "dangling object" messages too, but they
				1387	aren't interesting.)</p><p>Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
				1388	points to it. If you could find just one copy of that missing blob
				1389	object, possibly in some other repository, you could move it into
				1390	.git/objects/4b/9458b3… and be done. Suppose you can't. You can
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1391	still examine the tree that pointed to it with <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>,
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1392	which might output something like:</p><div class="literallayout"><p>$ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8<br>
				1393	100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore<br>
				1394	100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap<br>
				1395	100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING<br>
				1396	...<br>
				1397	100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile<br>
				1398	...</p></div><p>So now you know that the missing blob was the data for a file named
				1399	"myfile". And chances are you can also identify the directory—let's
				1400	say it's in "somedirectory". If you're lucky the missing copy might be
				1401	the same as the copy you have checked out in your working tree at
				1402	"somedirectory/myfile"; you can test whether that's right with
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1403	<a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a>:</p><div class="literallayout"><p>$ git hash-object -w somedirectory/myfile</p></div><p>which will create and store a blob object with the contents of
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1404	somedirectory/myfile, and output the SHA-1 of that object. if you're
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	1405	extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
				1406	which case you've guessed right, and the corruption is fixed!</p><p>Otherwise, you need more information. How do you tell which version of
				1407	the file has been lost?</p><p>The easiest way to do this is with:</p><div class="literallayout"><p>$ git log --raw --all --full-history -- somedirectory/myfile</p></div><p>Because you're asking for raw output, you'll now get something like</p><div class="literallayout"><p>commit abc<br>
				1408	Author:<br>
				1409	Date:<br>
				1410	...<br>
				1411	:100644 100644 4b9458b... newsha... M somedirectory/myfile<br>
				1412	<br>
				1413	<br>
				1414	commit xyz<br>
				1415	Author:<br>
				1416	Date:<br>
				1417	<br>
				1418	...<br>
				1419	:100644 100644 oldsha... 4b9458b... M somedirectory/myfile</p></div><p>This tells you that the immediately preceding version of the file was
				1420	"newsha", and that the immediately following version was "oldsha".
				1421	You also know the commit messages that went with the change from oldsha
				1422	to 4b9458b and with the change from 4b9458b to newsha.</p><p>If you've been committing small enough changes, you may now have a good
				1423	shot at reconstructing the contents of the in-between state 4b9458b.</p><p>If you can do that, you can now recreate the missing object with</p><div class="literallayout"><p>$ git hash-object -w <recreated-file></p></div><p>and your repository is good again!</p><p>(Btw, you could have ignored the fsck, and started with doing a</p><div class="literallayout"><p>$ git log --raw --all</p></div><p>and just looked for the sha of the missing object (4b9458b..) in that
				1424	whole thing. It's up to you - git does <span class="strong"><strong>have</strong></span> a lot of information, it is
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1425	just missing one particular blob version.</p></div></div><div class="section" title="The index"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-index"></a>The index</h2></div></div></div><p>The index is a binary file (generally kept in .git/index) containing a
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1426	sorted list of path names, each with permissions and the SHA-1 of a blob
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1427	object; <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> can show you the contents of the index:</p><div class="literallayout"><p>$ git ls-files --stage<br>
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1428	100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore<br>
				1429	100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap<br>
				1430	100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING<br>
				1431	100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore<br>
				1432	100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile<br>
				1433	...<br>
				1434	100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h<br>
				1435	100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c<br>
				1436	100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h</p></div><p>Note that in older documentation you may see the index called the
				1437	"current directory cache" or just the "cache". It has three important
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1438	properties:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p class="simpara">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1439	The index contains all the information necessary to generate a single
				1440	(uniquely determined) tree object.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1441	</p><p class="simpara">For example, running <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> generates this tree object
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1442	from the index, stores it in the object database, and uses it as the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1443	tree object associated with the new commit.</p></li><li class="listitem"><p class="simpara">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1444	The index enables fast comparisons between the tree object it defines
				1445	and the working tree.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1446	</p><p class="simpara">It does this by storing some additional data for each entry (such as
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1447	the last modified time). This data is not displayed above, and is not
				1448	stored in the created tree object, but it can be used to determine
				1449	quickly which files in the working directory differ from what was
				1450	stored in the index, and thus save git from having to read all of the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1451	data from such files to look for changes.</p></li><li class="listitem"><p class="simpara">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1452	It can efficiently represent information about merge conflicts
				1453	between different tree objects, allowing each pathname to be
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1454	associated with sufficient information about the trees involved that
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1455	you can create a three-way merge between them.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1456	</p><p class="simpara">We saw in <a class="xref" href="#conflict-resolution" title="Getting conflict-resolution help during a merge">the section called “Getting conflict-resolution help during a merge”</a> that during a merge the index can
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1457	store multiple versions of a single file (called "stages"). The third
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1458	column in the <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> output above is the stage
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1459	number, and will take on values other than 0 for files with merge
				1460	conflicts.</p></li></ol></div><p>The index is thus a sort of temporary staging area, which is filled with
				1461	a tree which you are in the process of working on.</p><p>If you blow the index away entirely, you generally haven't lost any
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1462	information as long as you have the name of the tree that it described.</p></div></div><div class="chapter" title="Chapter 8. Submodules"><div class="titlepage"><div><div><h2 class="title"><a name="submodules"></a>Chapter 8. Submodules</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#_pitfalls_with_submodules">Pitfalls with submodules</a></span></dt></dl></div><p>Large projects are often composed of smaller, self-contained modules. For
Junio C Hamano	4fd58d4	2007-09-30 00:51:14	[diff] [blame]	1463	example, an embedded Linux distribution's source tree would include every
				1464	piece of software in the distribution with some local modifications; a movie
				1465	player might need to build against a specific, known-working version of a
				1466	decompression library; several independent programs might all share the same
				1467	build scripts.</p><p>With centralized revision control systems this is often accomplished by
				1468	including every module in one single repository. Developers can check out
				1469	all modules or only the modules they need to work with. They can even modify
				1470	files across several modules in a single commit while moving things around
				1471	or updating APIs and translations.</p><p>Git does not allow partial checkouts, so duplicating this approach in Git
				1472	would force developers to keep a local copy of modules they are not
				1473	interested in touching. Commits in an enormous checkout would be slower
				1474	than you'd expect as Git would have to scan every directory for changes.
				1475	If modules have a lot of local history, clones would take forever.</p><p>On the plus side, distributed revision control systems can much better
				1476	integrate with external sources. In a centralized model, a single arbitrary
				1477	snapshot of the external project is exported from its own revision control
				1478	and then imported into the local revision control on a vendor branch. All
				1479	the history is hidden. With distributed revision control you can clone the
				1480	entire external history and much more easily follow development and re-merge
				1481	local changes.</p><p>Git's submodule support allows a repository to contain, as a subdirectory, a
				1482	checkout of an external project. Submodules maintain their own identity;
				1483	the submodule support just stores the submodule repository location and
				1484	commit ID, so other developers who clone the containing project
				1485	("superproject") can easily clone all the submodules at the same revision.
				1486	Partial checkouts of the superproject are possible: you can tell Git to
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1487	clone none, some or all of the submodules.</p><p>The <a class="ulink" href="git-submodule.html" target="_top">git-submodule(1)</a> command is available since Git 1.5.3. Users
Junio C Hamano	4fd58d4	2007-09-30 00:51:14	[diff] [blame]	1488	with Git 1.5.2 can look up the submodule commits in the repository and
				1489	manually check them out; earlier versions won't recognize the submodules at
				1490	all.</p><p>To see how submodule support works, create (for example) four example
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1491	repositories that can be used later as a submodule:</p><div class="literallayout"><p>$ mkdir ~/git<br>
				1492	$ cd ~/git<br>
				1493	$ for i in a b c d<br>
				1494	do<br>
				1495	mkdir $i<br>
				1496	cd $i<br>
				1497	git init<br>
				1498	echo "module $i" > $i.txt<br>
				1499	git add $i.txt<br>
				1500	git commit -m "Initial commit, submodule $i"<br>
				1501	cd ..<br>
				1502	done</p></div><p>Now create the superproject and add all the submodules:</p><div class="literallayout"><p>$ mkdir super<br>
				1503	$ cd super<br>
				1504	$ git init<br>
				1505	$ for i in a b c d<br>
				1506	do<br>
Junio C Hamano	7f80ae8	2008-07-30 18:31:35	[diff] [blame]	1507	git submodule add ~/git/$i $i<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1508	done</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Do not use local URLs here if you plan to publish your superproject!</p></div><p>See what files <code class="literal">git submodule</code> created:</p><div class="literallayout"><p>$ ls -a<br>
				1509	. .. .git .gitmodules a b c d</p></div><p>The <code class="literal">git submodule add <repo> <path></code> command does a couple of things:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	7f80ae8	2008-07-30 18:31:35	[diff] [blame]	1510	It clones the submodule from <repo> to the given <path> under the
				1511	current directory and by default checks out the master branch.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1512	</li><li class="listitem">
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1513	It adds the submodule's clone path to the <a class="ulink" href="gitmodules.html" target="_top">gitmodules(5)</a> file and
Junio C Hamano	4fd58d4	2007-09-30 00:51:14	[diff] [blame]	1514	adds this file to the index, ready to be committed.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1515	</li><li class="listitem">
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1516	It adds the submodule's current commit ID to the index, ready to be
				1517	committed.
				1518	</li></ul></div><p>Commit the superproject:</p><div class="literallayout"><p>$ git commit -m "Add submodules a, b, c and d."</p></div><p>Now clone the superproject:</p><div class="literallayout"><p>$ cd ..<br>
				1519	$ git clone super cloned<br>
				1520	$ cd cloned</p></div><p>The submodule directories are there, but they're empty:</p><div class="literallayout"><p>$ ls -a a<br>
				1521	. ..<br>
				1522	$ git submodule status<br>
				1523	-d266b9873ad50488163457f025db7cdd9683d88b a<br>
				1524	-e81d457da15309b4fef4249aba9b50187999670d b<br>
				1525	-c1536a972b9affea0f16e0680ba87332dc059146 c<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1526	-d96249ff5d57de5de093e6baff9e0aafa5276a74 d</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The commit object names shown above would be different for you, but they
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1527	should match the HEAD commit object names of your repositories. You can check
				1528	it by running <code class="literal">git ls-remote ../a</code>.</p></div><p>Pulling down the submodules is a two-step process. First run <code class="literal">git submodule
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1529	init</code> to add the submodule repository URLs to <code class="literal">.git/config</code>:</p><div class="literallayout"><p>$ git submodule init</p></div><p>Now use <code class="literal">git submodule update</code> to clone the repositories and check out the
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1530	commits specified in the superproject:</p><div class="literallayout"><p>$ git submodule update<br>
				1531	$ cd a<br>
				1532	$ ls -a<br>
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1533	. .. .git a.txt</p></div><p>One major difference between <code class="literal">git submodule update</code> and <code class="literal">git submodule add</code> is
				1534	that <code class="literal">git submodule update</code> checks out a specific commit, rather than the tip
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1535	of a branch. It's like checking out a tag: the head is detached, so you're not
				1536	working on a branch.</p><div class="literallayout"><p>$ git branch<br>
				1537	* (no branch)<br>
				1538	master</p></div><p>If you want to make a change within a submodule and you have a detached head,
				1539	then you should create or checkout a branch, make your changes, publish the
				1540	change within the submodule, and then update the superproject to reference the
				1541	new commit:</p><div class="literallayout"><p>$ git checkout master</p></div><p>or</p><div class="literallayout"><p>$ git checkout -b fix-up</p></div><p>then</p><div class="literallayout"><p>$ echo "adding a line again" >> a.txt<br>
				1542	$ git commit -a -m "Updated the submodule from within the superproject."<br>
				1543	$ git push<br>
				1544	$ cd ..<br>
				1545	$ git diff<br>
				1546	diff --git a/a b/a<br>
				1547	index d266b98..261dfac 160000<br>
				1548	--- a/a<br>
				1549	+++ b/a<br>
				1550	@@ -1 +1 @@<br>
				1551	-Subproject commit d266b9873ad50488163457f025db7cdd9683d88b<br>
				1552	+Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24<br>
				1553	$ git add a<br>
				1554	$ git commit -m "Updated submodule a."<br>
				1555	$ git push</p></div><p>You have to run <code class="literal">git submodule update</code> after <code class="literal">git pull</code> if you want to update
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1556	submodules, too.</p><div class="section" title="Pitfalls with submodules"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_pitfalls_with_submodules"></a>Pitfalls with submodules</h2></div></div></div><p>Always publish the submodule change before publishing the change to the
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1557	superproject that references it. If you forget to publish the submodule change,
				1558	others won't be able to clone the repository:</p><div class="literallayout"><p>$ cd ~/git/super/a<br>
				1559	$ echo i added another line to this file >> a.txt<br>
				1560	$ git commit -a -m "doing it wrong this time"<br>
				1561	$ cd ..<br>
				1562	$ git add a<br>
				1563	$ git commit -m "Updated submodule a again."<br>
				1564	$ git push<br>
				1565	$ cd ~/git/cloned<br>
				1566	$ git pull<br>
				1567	$ git submodule update<br>
				1568	error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.<br>
				1569	Did you forget to 'git add'?<br>
Junio C Hamano	2b186d8	2010-02-02 07:17:34	[diff] [blame]	1570	Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'</p></div><p>In older git versions it could be easily forgotten to commit new or modified
				1571	files in a submodule, which silently leads to similar problems as not pushing
				1572	the submodule changes. Starting with git 1.7.0 both "git status" and "git diff"
				1573	in the superproject show submodules as modified when they contain new or
				1574	modified files to protect against accidentally committing such a state. "git
				1575	diff" will also add a "-dirty" to the work tree side when generating patch
				1576	output or used with the —submodule option:</p><div class="literallayout"><p>$ git diff<br>
				1577	diff --git a/sub b/sub<br>
				1578	--- a/sub<br>
				1579	+++ b/sub<br>
				1580	@@ -1 +1 @@<br>
				1581	-Subproject commit 3f356705649b5d566d97ff843cf193359229a453<br>
				1582	+Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty<br>
				1583	$ git diff --submodule<br>
				1584	Submodule sub 3f35670..3f35670-dirty:</p></div><p>You also should not rewind branches in a submodule beyond commits that were
Junio C Hamano	9810d63	2007-09-24 01:05:34	[diff] [blame]	1585	ever recorded in any superproject.</p><p>It's not safe to run <code class="literal">git submodule update</code> if you've made and committed
				1586	changes within a submodule without checking out a branch first. They will be
				1587	silently overwritten:</p><div class="literallayout"><p>$ cat a.txt<br>
				1588	module a<br>
				1589	$ echo line added from private2 >> a.txt<br>
				1590	$ git commit -a -m "line added inside private2"<br>
				1591	$ cd ..<br>
				1592	$ git submodule update<br>
				1593	Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'<br>
				1594	$ cd a<br>
				1595	$ cat a.txt<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1596	module a</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The changes are still visible in the submodule's reflog.</p></div><p>This is not the case if you did not commit your changes.</p></div></div><div class="chapter" title="Chapter 9. Low-level git operations"><div class="titlepage"><div><div><h2 class="title"><a name="low-level-operations"></a>Chapter 9. Low-level git operations</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory -> index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index -> object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database -> index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index -> working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></div><p>Many of the higher-level commands were originally implemented as shell
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1597	scripts using a smaller core of low-level git commands. These can still
				1598	be useful when doing unusual things with git, or just as a way to
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1599	understand its inner workings.</p><div class="section" title="Object access and manipulation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-manipulation"></a>Object access and manipulation</h2></div></div></div><p>The <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> command can show the contents of any object,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1600	though the higher-level <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> is usually more useful.</p><p>The <a class="ulink" href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> command allows constructing commits with
				1601	arbitrary parents and trees.</p><p>A tree can be created with <a class="ulink" href="git-write-tree.html" target="_top">git-write-tree(1)</a> and its data can be
				1602	accessed by <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. Two trees can be compared with
				1603	<a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>.</p><p>A tag is created with <a class="ulink" href="git-mktag.html" target="_top">git-mktag(1)</a>, and the signature can be
				1604	verified by <a class="ulink" href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>, though it is normally simpler to
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1605	use <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> for both.</p></div><div class="section" title="The Workflow"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-workflow"></a>The Workflow</h2></div></div></div><p>High-level operations such as <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1606	<a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a> and <a class="ulink" href="git-reset.html" target="_top">git-reset(1)</a> work by moving data
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1607	between the working tree, the index, and the object database. Git
				1608	provides low-level operations which perform each of these steps
				1609	individually.</p><p>Generally, all "git" operations work on the index file. Some operations
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1610	work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1611	index), but most operations move data between the index file and either
				1612	the database or the working directory. Thus there are four main
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1613	combinations:</p><div class="section" title="working directory -> index"><div class="titlepage"><div><div><h3 class="title"><a name="working-directory-to-index"></a>working directory -> index</h3></div></div></div><p>The <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a> command updates the index with
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1614	information from the working directory. You generally update the
				1615	index information by just specifying the filename you want to update,
				1616	like so:</p><div class="literallayout"><p>$ git update-index filename</p></div><p>but to avoid common mistakes with filename globbing etc, the command
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1617	will not normally add totally new entries or remove old entries,
				1618	i.e. it will normally just update existing cache entries.</p><p>To tell git that yes, you really do realize that certain files no
				1619	longer exist, or that new files should be added, you
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1620	should use the <code class="literal">—remove</code> and <code class="literal">—add</code> flags respectively.</p><p>NOTE! A <code class="literal">—remove</code> flag does <span class="emphasis"><em>not</em></span> mean that subsequent filenames will
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1621	necessarily be removed: if the files still exist in your directory
				1622	structure, the index will be updated with their new status, not
Junio C Hamano	774239c	2007-12-01 01:57:43	[diff] [blame]	1623	removed. The only thing <code class="literal">—remove</code> means is that update-index will be
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1624	considering a removed file to be a valid thing, and if the file really
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1625	does not exist any more, it will update the index accordingly.</p><p>As a special case, you can also do <code class="literal">git update-index —refresh</code>, which
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1626	will refresh the "stat" information of each index to match the current
				1627	stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and
				1628	it will only update the fields that are used to quickly test whether
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1629	an object still matches its old backing store object.</p><p>The previously introduced <a class="ulink" href="git-add.html" target="_top">git-add(1)</a> is just a wrapper for
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1630	<a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a>.</p></div><div class="section" title="index -> object database"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-object-database"></a>index -> object database</h3></div></div></div><p>You write your current index file to a "tree" object with the program</p><div class="literallayout"><p>$ git write-tree</p></div><p>that doesn't come with any options—it will just write out the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1631	current index into the set of tree objects that describe that state,
				1632	and it will return the name of the resulting top-level tree. You can
				1633	use that tree to re-generate the index at any time by going in the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1634	other direction:</p></div><div class="section" title="object database -> index"><div class="titlepage"><div><div><h3 class="title"><a name="object-database-to-index"></a>object database -> index</h3></div></div></div><p>You read a "tree" file from the object database, and use that to
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1635	populate (and overwrite—don't do this if your index contains any
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1636	unsaved state that you might want to restore later!) your current
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1637	index. Normal operation is just</p><div class="literallayout"><p>$ git read-tree <SHA-1 of tree></p></div><p>and your index file will now be equivalent to the tree that you saved
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1638	earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1639	directory contents have not been modified.</p></div><div class="section" title="index -> working directory"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-working-directory"></a>index -> working directory</h3></div></div></div><p>You update your working directory from the index by "checking out"
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1640	files. This is not a very common operation, since normally you'd just
				1641	keep your files updated, and rather than write to your working
				1642	directory, you'd tell the index files about the changes in your
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1643	working directory (i.e. <code class="literal">git update-index</code>).</p><p>However, if you decide to jump to a new version, or check out somebody
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1644	else's version, or just restore a previous tree, you'd populate your
				1645	index file with read-tree, and then you need to check out the result
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1646	with</p><div class="literallayout"><p>$ git checkout-index filename</p></div><p>or, if you want to check out all of the index, use <code class="literal">-a</code>.</p><p>NOTE! <code class="literal">git checkout-index</code> normally refuses to overwrite old files, so
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1647	if you have an old version of the tree already checked out, you will
				1648	need to use the "-f" flag (<span class="emphasis"><em>before</em></span> the "-a" flag or the filename) to
				1649	<span class="emphasis"><em>force</em></span> the checkout.</p><p>Finally, there are a few odds and ends which are not purely moving
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1650	from one representation to the other:</p></div><div class="section" title="Tying it all together"><div class="titlepage"><div><div><h3 class="title"><a name="tying-it-all-together"></a>Tying it all together</h3></div></div></div><p>To commit a tree you have instantiated with "git write-tree", you'd
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1651	create a "commit" object that refers to that tree and the history
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1652	behind it—most notably the "parent" commits that preceded it in
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1653	history.</p><p>Normally a "commit" has one parent: the previous state of the tree
				1654	before a certain change was made. However, sometimes it can have two
				1655	or more parent commits, in which case we call it a "merge", due to the
				1656	fact that such a commit brings together ("merges") two or more
				1657	previous states represented by other commits.</p><p>In other words, while a "tree" represents a particular directory state
				1658	of a working directory, a "commit" represents that state in "time",
				1659	and explains how we got there.</p><p>You create a commit object by giving it the tree that describes the
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1660	state at the time of the commit, and a list of parents:</p><div class="literallayout"><p>$ git commit-tree <tree> -p <parent> [-p <parent2> ..]</p></div><p>and then giving the reason for the commit on stdin (either through
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1661	redirection from a pipe or file, or by just typing it at the tty).</p><p><code class="literal">git commit-tree</code> will return the name of the object that represents
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1662	that commit, and you should save it away for later use. Normally,
				1663	you'd commit a new <code class="literal">HEAD</code> state, and while git doesn't care where you
				1664	save the note about that state, in practice we tend to just write the
				1665	result to the file pointed at by <code class="literal">.git/HEAD</code>, so that we can always see
				1666	what the last committed state was.</p><p>Here is an ASCII art by Jon Loeliger that illustrates how
				1667	various pieces fit together.</p><div class="literallayout"><p><br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1668	commit-tree<br>
				1669	commit obj<br>
				1670	+----+<br>
				1671	\| \|<br>
				1672	\| \|<br>
				1673	V V<br>
				1674	+-----------+<br>
				1675	\| Object DB \|<br>
				1676	\| Backing \|<br>
				1677	\| Store \|<br>
				1678	+-----------+<br>
				1679	^<br>
				1680	write-tree \| \|<br>
				1681	tree obj \| \|<br>
				1682	\| \| read-tree<br>
				1683	\| \| tree obj<br>
				1684	V<br>
				1685	+-----------+<br>
				1686	\| Index \|<br>
				1687	\| "cache" \|<br>
				1688	+-----------+<br>
				1689	update-index ^<br>
				1690	blob obj \| \|<br>
				1691	\| \|<br>
				1692	checkout-index -u \| \| checkout-index<br>
				1693	stat \| \| blob obj<br>
				1694	V<br>
				1695	+-----------+<br>
				1696	\| Working \|<br>
				1697	\| Directory \|<br>
				1698	+-----------+<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1699	</p></div></div></div><div class="section" title="Examining the data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-the-data"></a>Examining the data</h2></div></div></div><p>You can examine the data represented in the object database and the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1700	index with various helper tools. For every object, you can use
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1701	<a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1702	object:</p><div class="literallayout"><p>$ git cat-file -t <objectname></p></div><p>shows the type of the object, and once you have the type (which is
				1703	usually implicit in where you find the object), you can use</p><div class="literallayout"><p>$ git cat-file blob\|tree\|commit\|tag <objectname></p></div><p>to show its contents. NOTE! Trees have binary content, and as a result
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1704	there is a special helper for showing that content, called
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1705	<code class="literal">git ls-tree</code>, which turns the binary content into a more easily
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1706	readable form.</p><p>It's especially instructive to look at "commit" objects, since those
				1707	tend to be small and fairly self-explanatory. In particular, if you
				1708	follow the convention of having the top commit name in <code class="literal">.git/HEAD</code>,
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1709	you can do</p><div class="literallayout"><p>$ git cat-file commit HEAD</p></div><p>to see what the top commit was.</p></div><div class="section" title="Merging multiple trees"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees"></a>Merging multiple trees</h2></div></div></div><p>Git helps you do a three-way merge, which you can expand to n-way by
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1710	repeating the merge procedure arbitrary times until you finally
				1711	"commit" the state. The normal situation is that you'd only do one
				1712	three-way merge (two parents), and commit it, but if you like to, you
				1713	can do multiple parents in one go.</p><p>To do a three-way merge, you need the two sets of "commit" objects
				1714	that you want to merge, use those to find the closest common parent (a
				1715	third "commit" object), and then use those commit objects to find the
				1716	state of the directory ("tree" object) at these points.</p><p>To get the "base" for the merge, you first look up the common parent
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1717	of two commits with</p><div class="literallayout"><p>$ git merge-base <commit1> <commit2></p></div><p>which will return you the commit they are both based on. You should
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1718	now look up the "tree" objects of those commits, which you can easily
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1719	do with (for example)</p><div class="literallayout"><p>$ git cat-file commit <commitname> \| head -1</p></div><p>since the tree object information is always the first line in a commit
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1720	object.</p><p>Once you know the three trees you are going to merge (the one "original"
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	1721	tree, aka the common tree, and the two "result" trees, aka the branches
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1722	you want to merge), you do a "merge" read into the index. This will
				1723	complain if it has to throw away your old index contents, so you should
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1724	make sure that you've committed those—in fact you would normally
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1725	always do a merge against your last commit (which should thus match what
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1726	you have in your current index anyway).</p><p>To do the merge, do</p><div class="literallayout"><p>$ git read-tree -m -u <origtree> <yourtree> <targettree></p></div><p>which will do all trivial merge operations for you directly in the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1727	index file, and you can just write the result out with
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1728	<code class="literal">git write-tree</code>.</p></div><div class="section" title="Merging multiple trees, continued"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees-2"></a>Merging multiple trees, continued</h2></div></div></div><p>Sadly, many merges aren't trivial. If there are files that have
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1729	been added, moved or removed, or if both branches have modified the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1730	same file, you will be left with an index tree that contains "merge
				1731	entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree
				1732	object, and you will have to resolve any such merge clashes using
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1733	other tools before you can write out the result.</p><p>You can examine such index state with <code class="literal">git ls-files —unmerged</code>
				1734	command. An example:</p><div class="literallayout"><p>$ git read-tree -m $orig HEAD $target<br>
				1735	$ git ls-files --unmerged<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1736	100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c<br>
				1737	100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c<br>
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1738	100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c</p></div><p>Each line of the <code class="literal">git ls-files —unmerged</code> output begins with
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1739	the blob mode bits, blob SHA-1, <span class="emphasis"><em>stage number</em></span>, and the
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1740	filename. The <span class="emphasis"><em>stage number</em></span> is git's way to say which tree it
				1741	came from: stage 1 corresponds to <code class="literal">$orig</code> tree, stage 2 <code class="literal">HEAD</code>
				1742	tree, and stage3 <code class="literal">$target</code> tree.</p><p>Earlier we said that trivial merges are done inside
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1743	<code class="literal">git read-tree -m</code>. For example, if the file did not change
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1744	from <code class="literal">$orig</code> to <code class="literal">HEAD</code> nor <code class="literal">$target</code>, or if the file changed
				1745	from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way,
				1746	obviously the final outcome is what is in <code class="literal">HEAD</code>. What the
				1747	above example shows is that file <code class="literal">hello.c</code> was changed from
				1748	<code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> in a different way.
				1749	You could resolve this by running your favorite 3-way merge
Junio C Hamano	3d30fd5	2007-05-08 00:32:53	[diff] [blame]	1750	program, e.g. <code class="literal">diff3</code>, <code class="literal">merge</code>, or git's own merge-file, on
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1751	the blob objects from these three stages yourself, like this:</p><div class="literallayout"><p>$ git cat-file blob 263414f... >hello.c~1<br>
				1752	$ git cat-file blob 06fa6a2... >hello.c~2<br>
				1753	$ git cat-file blob cc44c73... >hello.c~3<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1754	$ git merge-file hello.c~2 hello.c~1 hello.c~3</p></div><p>This would leave the merge result in <code class="literal">hello.c~2</code> file, along
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1755	with conflict markers if there are conflicts. After verifying
				1756	the merge result makes sense, you can tell git what the final
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1757	merge result for this file is by:</p><div class="literallayout"><p>$ mv -f hello.c~2 hello.c<br>
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1758	$ git update-index hello.c</p></div><p>When a path is in the "unmerged" state, running <code class="literal">git update-index</code> for
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1759	that path tells git to mark the path resolved.</p><p>The above is the description of a git merge at the lowest level,
				1760	to help you understand what conceptually happens under the hood.
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1761	In practice, nobody, not even git itself, runs <code class="literal">git cat-file</code> three times
				1762	for this. There is a <code class="literal">git merge-index</code> program that extracts the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1763	stages to temporary files and calls a "merge" script on it:</p><div class="literallayout"><p>$ git merge-index git-merge-one-file hello.c</p></div><p>and that is what higher level <code class="literal">git merge -s resolve</code> is implemented with.</p></div></div><div class="chapter" title="Chapter 10. Hacking git"><div class="titlepage"><div><div><h2 class="title"><a name="hacking-git"></a>Chapter 10. Hacking git</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git's source code</a></span></dt></dl></div><p>This chapter covers internal details of the git implementation which
				1764	probably only git developers need to understand.</p><div class="section" title="Object storage format"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-details"></a>Object storage format</h2></div></div></div><p>All objects have a statically determined "type" which identifies the
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1765	format of the object (i.e. how it is used, and how it can refer to other
				1766	objects). There are currently four different object types: "blob",
				1767	"tree", "commit", and "tag".</p><p>Regardless of object type, all objects share the following
				1768	characteristics: they are all deflated with zlib, and have a header
				1769	that not only specifies their type, but also provides size information
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1770	about the data in the object. It's worth noting that the SHA-1 hash
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1771	that is used to name the object is the hash of the original data
				1772	plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name
				1773	for <span class="emphasis"><em>file</em></span>.
				1774	(Historical note: in the dawn of the age of git the hash
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1775	was the SHA-1 of the <span class="emphasis"><em>compressed</em></span> object.)</p><p>As a result, the general consistency of an object can always be tested
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1776	independently of the contents or the type of the object: all objects can
				1777	be validated by verifying that (a) their hashes match the content of the
				1778	file and (b) the object successfully inflates to a stream of bytes that
				1779	forms a sequence of <ascii type without space> + <space> + <ascii decimal
				1780	size> + <byte\0> + <binary object data>.</p><p>The structured objects can further have their structure and
				1781	connectivity to other objects verified. This is generally done with
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1782	the <code class="literal">git fsck</code> program, which generates a full dependency graph
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	1783	of all objects, and verifies their internal consistency (in addition
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1784	to just verifying their superficial consistency through the hash).</p></div><div class="section" title="A birds-eye view of Git's source code"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="birdview-on-the-source-code"></a>A birds-eye view of Git's source code</h2></div></div></div><p>It is not always easy for new developers to find their way through Git's
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1785	source code. This section gives you a little guidance to show where to
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1786	start.</p><p>A good place to start is with the contents of the initial commit, with:</p><div class="literallayout"><p>$ git checkout e83c5163</p></div><p>The initial revision lays the foundation for almost everything git has
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1787	today, but is small enough to read in one sitting.</p><p>Note that terminology has changed since that revision. For example, the
				1788	README in that revision uses the word "changeset" to describe what we
Junio C Hamano	d32738e	2008-07-09 19:53:42	[diff] [blame]	1789	now call a <a class="link" href="#def_commit_object">commit</a>.</p><p>Also, we do not call it "cache" any more, but rather "index"; however, the
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1790	file is still called <code class="literal">cache.h</code>. Remark: Not much reason to change it now,
				1791	especially since there is no good single name for it anyway, because it is
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1792	basically _the_ header file which is included by _all_ of Git's C sources.</p><p>If you grasp the ideas in that initial commit, you should check out a
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1793	more recent version and skim <code class="literal">cache.h</code>, <code class="literal">object.h</code> and <code class="literal">commit.h</code>.</p><p>In the early days, Git (in the tradition of UNIX) was a bunch of programs
				1794	which were extremely simple, and which you used in scripts, piping the
				1795	output of one into another. This turned out to be good for initial
				1796	development, since it was easier to test new things. However, recently
				1797	many of these parts have become builtins, and some of the core has been
				1798	"libified", i.e. put into libgit.a for performance, portability reasons,
				1799	and to avoid code duplication.</p><p>By now, you know what the index is (and find the corresponding data
				1800	structures in <code class="literal">cache.h</code>), and that there are just a couple of object types
				1801	(blobs, trees, commits and tags) which inherit their common structure from
				1802	<code class="literal">struct object</code>, which is their first member (and thus, you can cast e.g.
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1803	<code class="literal">(struct object *)commit</code> to achieve the _same_ as <code class="literal">&commit->object</code>, i.e.
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1804	get at the object name and flags).</p><p>Now is a good point to take a break to let this information sink in.</p><p>Next step: get familiar with the object naming. Read <a class="xref" href="#naming-commits" title="Naming commits">the section called “Naming commits”</a>.
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1805	There are quite a few ways to name an object (and not only revisions!).
				1806	All of these are handled in <code class="literal">sha1_name.c</code>. Just have a quick look at
				1807	the function <code class="literal">get_sha1()</code>. A lot of the special handling is done by
				1808	functions like <code class="literal">get_sha1_basic()</code> or the likes.</p><p>This is just to get you into the groove for the most libified part of Git:
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1809	the revision walker.</p><p>Basically, the initial version of <code class="literal">git log</code> was a shell script:</p><div class="literallayout"><p>$ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") \| \<br>
				1810	LESS=-S ${PAGER:-less}</p></div><p>What does this mean?</p><p><code class="literal">git rev-list</code> is the original version of the revision walker, which
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1811	_always_ printed a list of revisions to stdout. It is still functional,
Junio C Hamano	27a128b	2009-08-13 01:23:00	[diff] [blame]	1812	and needs to, since most new Git commands start out as scripts using
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1813	<code class="literal">git rev-list</code>.</p><p><code class="literal">git rev-parse</code> is not as important any more; it was only used to filter out
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1814	options that were relevant for the different plumbing commands that were
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1815	called by the script.</p><p>Most of what <code class="literal">git rev-list</code> did is contained in <code class="literal">revision.c</code> and
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1816	<code class="literal">revision.h</code>. It wraps the options in a struct named <code class="literal">rev_info</code>, which
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1817	controls how and what revisions are walked, and more.</p><p>The original job of <code class="literal">git rev-parse</code> is now taken by the function
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1818	<code class="literal">setup_revisions()</code>, which parses the revisions and the common command line
				1819	options for the revision walker. This information is stored in the struct
				1820	<code class="literal">rev_info</code> for later consumption. You can do your own command line option
				1821	parsing after calling <code class="literal">setup_revisions()</code>. After that, you have to call
				1822	<code class="literal">prepare_revision_walk()</code> for initialization, and then you can get the
				1823	commits one by one with the function <code class="literal">get_revision()</code>.</p><p>If you are interested in more details of the revision walking process,
				1824	just have a look at the first implementation of <code class="literal">cmd_log()</code>; call
Junio C Hamano	fce7c7e	2008-07-02 03:06:38	[diff] [blame]	1825	<code class="literal">git show v1.3.0~155^2~4</code> and scroll down to that function (note that you
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1826	no longer need to call <code class="literal">setup_pager()</code> directly).</p><p>Nowadays, <code class="literal">git log</code> is a builtin, which means that it is _contained_ in the
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1827	command <code class="literal">git</code>. The source side of a builtin is</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1828	a function called <code class="literal">cmd_<bla></code>, typically defined in <code class="literal">builtin-<bla>.c</code>,
				1829	and declared in <code class="literal">builtin.h</code>,
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1830	</li><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1831	an entry in the <code class="literal">commands[]</code> array in <code class="literal">git.c</code>, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1832	</li><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1833	an entry in <code class="literal">BUILTIN_OBJECTS</code> in the <code class="literal">Makefile</code>.
				1834	</li></ul></div><p>Sometimes, more than one builtin is contained in one source file. For
				1835	example, <code class="literal">cmd_whatchanged()</code> and <code class="literal">cmd_log()</code> both reside in <code class="literal">builtin-log.c</code>,
				1836	since they share quite a bit of code. In that case, the commands which are
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1837	_not_ named like the <code class="literal">.c</code> file in which they live have to be listed in
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1838	<code class="literal">BUILT_INS</code> in the <code class="literal">Makefile</code>.</p><p><code class="literal">git log</code> looks more complicated in C than it does in the original script,
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1839	but that allows for a much greater flexibility and performance.</p><p>Here again it is a good point to take a pause.</p><p>Lesson three is: study the code. Really, it is the best way to learn about
				1840	the organization of Git (after you know the basic concepts).</p><p>So, think about something which you are interested in, say, "how can I
				1841	access a blob just knowing the object name of it?". The first step is to
				1842	find a Git command with which you can do it. In this example, it is either
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1843	<code class="literal">git show</code> or <code class="literal">git cat-file</code>.</p><p>For the sake of clarity, let's stay with <code class="literal">git cat-file</code>, because it</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1844	is plumbing, and
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1845	</li><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1846	was around even in the initial commit (it literally went only through
				1847	some 20 revisions as <code class="literal">cat-file.c</code>, was renamed to <code class="literal">builtin-cat-file.c</code>
				1848	when made a builtin, and then saw less than 10 versions).
				1849	</li></ul></div><p>So, look into <code class="literal">builtin-cat-file.c</code>, search for <code class="literal">cmd_cat_file()</code> and look what
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1850	it does.</p><div class="literallayout"><p> git_config(git_default_config);<br>
				1851	if (argc != 3)<br>
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1852	usage("git cat-file [-t\|-s\|-e\|-p\|<type>] <sha1>");<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1853	if (get_sha1(argv[2], sha1))<br>
				1854	die("Not a valid object name %s", argv[2]);</p></div><p>Let's skip over the obvious details; the only really interesting part
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1855	here is the call to <code class="literal">get_sha1()</code>. It tries to interpret <code class="literal">argv[2]</code> as an
				1856	object name, and if it refers to an object which is present in the current
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1857	repository, it writes the resulting SHA-1 into the variable <code class="literal">sha1</code>.</p><p>Two things are interesting here:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1858	<code class="literal">get_sha1()</code> returns 0 on _success_. This might surprise some new
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1859	Git hackers, but there is a long tradition in UNIX to return different
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1860	negative numbers in case of different errors—and 0 on success.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1861	</li><li class="listitem">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1862	the variable <code class="literal">sha1</code> in the function signature of <code class="literal">get_sha1()</code> is <code class="literal">unsigned
				1863	char *</code>, but is actually expected to be a pointer to <code class="literal">unsigned
				1864	char[20]</code>. This variable will contain the 160-bit SHA-1 of the given
				1865	commit. Note that whenever a SHA-1 is passed as <code class="literal">unsigned char *</code>, it
				1866	is the binary representation, as opposed to the ASCII representation in
				1867	hex characters, which is passed as <code class="literal">char *</code>.
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1868	</li></ul></div><p>You will see both of these things throughout the code.</p><p>Now, for the meat:</p><div class="literallayout"><p> case 0:<br>
				1869	buf = read_object_with_reference(sha1, argv[1], &size, NULL);</p></div><p>This is how you read a blob (actually, not only a blob, but any type of
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1870	object). To know how the function <code class="literal">read_object_with_reference()</code> actually
				1871	works, find the source code for it (something like <code class="literal">git grep
				1872	read_object_with \| grep ":[a-z]"</code> in the git repository), and read
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1873	the source.</p><p>To find out how the result can be used, just read on in <code class="literal">cmd_cat_file()</code>:</p><div class="literallayout"><p> write_or_die(1, buf, size);</p></div><p>Sometimes, you do not know where to look for a feature. In many such cases,
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	1874	it helps to search through the output of <code class="literal">git log</code>, and then <code class="literal">git show</code> the
				1875	corresponding commit.</p><p>Example: If you know that there was some test case for <code class="literal">git bundle</code>, but
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	1876	do not remember where it was (yes, you _could_ <code class="literal">git grep bundle t/</code>, but that
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	1877	does not illustrate the point!):</p><div class="literallayout"><p>$ git log --no-merges t/</p></div><p>In the pager (<code class="literal">less</code>), just search for "bundle", go a few lines back,
				1878	and see that it is in commit 18449ab0… Now just copy this object name,
				1879	and paste it into the command line</p><div class="literallayout"><p>$ git show 18449ab0</p></div><p>Voila.</p><p>Another example: Find out what to do in order to make some script a
				1880	builtin:</p><div class="literallayout"><p>$ git log --no-merges --diff-filter=A builtin-*.c</p></div><p>You see, Git is actually the best tool to find out about the source of Git
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1881	itself!</p></div></div><div class="chapter" title="Chapter 11. Git Glossary"><div class="titlepage"><div><div><h2 class="title"><a name="glossary"></a>Chapter 11. Git Glossary</h2></div></div></div><div class="variablelist"><dl><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1882	<a name="def_alternate_object_database"></a>alternate object database
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1883	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1884	Via the alternates mechanism, a <a class="link" href="#def_repository">repository</a>
				1885	can inherit part of its <a class="link" href="#def_object_database">object database</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1886	from another object database, which is called "alternate".
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1887	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1888	<a name="def_bare_repository"></a>bare repository
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1889	</span></dt><dd>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1890	A bare repository is normally an appropriately
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1891	named <a class="link" href="#def_directory">directory</a> with a <code class="literal">.git</code> suffix that does not
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1892	have a locally checked-out copy of any of the files under
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	1893	revision control. That is, all of the <code class="literal">git</code>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1894	administrative and control files that would normally be present in the
				1895	hidden <code class="literal">.git</code> sub-directory are directly present in the
				1896	<code class="literal">repository.git</code> directory instead,
				1897	and no other files are present and checked out. Usually publishers of
				1898	public repositories make bare repositories available.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1899	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1900	<a name="def_blob_object"></a>blob object
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1901	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1902	Untyped <a class="link" href="#def_object">object</a>, e.g. the contents of a file.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1903	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1904	<a name="def_branch"></a>branch
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1905	</span></dt><dd>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1906	A "branch" is an active line of development. The most recent
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1907	<a class="link" href="#def_commit">commit</a> on a branch is referred to as the tip of
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1908	that branch. The tip of the branch is referenced by a branch
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1909	<a class="link" href="#def_head">head</a>, which moves forward as additional development
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1910	is done on the branch. A single git
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1911	<a class="link" href="#def_repository">repository</a> can track an arbitrary number of
				1912	branches, but your <a class="link" href="#def_working_tree">working tree</a> is
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1913	associated with just one of them (the "current" or "checked out"
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1914	branch), and <a class="link" href="#def_HEAD">HEAD</a> points to that branch.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1915	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1916	<a name="def_cache"></a>cache
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1917	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1918	Obsolete for: <a class="link" href="#def_index">index</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1919	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1920	<a name="def_chain"></a>chain
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1921	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1922	A list of objects, where each <a class="link" href="#def_object">object</a> in the list contains
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1923	a reference to its successor (for example, the successor of a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1924	<a class="link" href="#def_commit">commit</a> could be one of its <a class="link" href="#def_parent">parents</a>).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1925	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1926	<a name="def_changeset"></a>changeset
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1927	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1928	BitKeeper/cvsps speak for "<a class="link" href="#def_commit">commit</a>". Since git does not
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1929	store changes, but states, it really does not make sense to use the term
				1930	"changesets" with git.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1931	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1932	<a name="def_checkout"></a>checkout
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1933	</span></dt><dd>
Junio C Hamano	a14a403	2008-03-25 09:11:02	[diff] [blame]	1934	The action of updating all or part of the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1935	<a class="link" href="#def_working_tree">working tree</a> with a <a class="link" href="#def_tree_object">tree object</a>
				1936	or <a class="link" href="#def_blob_object">blob</a> from the
				1937	<a class="link" href="#def_object_database">object database</a>, and updating the
				1938	<a class="link" href="#def_index">index</a> and <a class="link" href="#def_HEAD">HEAD</a> if the whole working tree has
				1939	been pointed at a new <a class="link" href="#def_branch">branch</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1940	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1941	<a name="def_cherry-picking"></a>cherry-picking
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1942	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1943	In <a class="link" href="#def_SCM">SCM</a> jargon, "cherry pick" means to choose a subset of
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1944	changes out of a series of changes (typically commits) and record them
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	1945	as a new series of changes on top of a different codebase. In GIT, this is
				1946	performed by the "git cherry-pick" command to extract the change introduced
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1947	by an existing <a class="link" href="#def_commit">commit</a> and to record it based on the tip
				1948	of the current <a class="link" href="#def_branch">branch</a> as a new commit.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1949	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1950	<a name="def_clean"></a>clean
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1951	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1952	A <a class="link" href="#def_working_tree">working tree</a> is clean, if it
				1953	corresponds to the <a class="link" href="#def_revision">revision</a> referenced by the current
				1954	<a class="link" href="#def_head">head</a>. Also see "<a class="link" href="#def_dirty">dirty</a>".
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1955	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1956	<a name="def_commit"></a>commit
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1957	</span></dt><dd><p class="simpara">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1958	As a noun: A single point in the
				1959	git history; the entire history of a project is represented as a
				1960	set of interrelated commits. The word "commit" is often
				1961	used by git in the same places other revision control systems
				1962	use the words "revision" or "version". Also used as a short
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1963	hand for <a class="link" href="#def_commit_object">commit object</a>.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	1964	</p><p class="simpara">As a verb: The action of storing a new snapshot of the project's
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1965	state in the git history, by creating a new commit representing the current
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1966	state of the <a class="link" href="#def_index">index</a> and advancing <a class="link" href="#def_HEAD">HEAD</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1967	to point at the new commit.</p></dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1968	<a name="def_commit_object"></a>commit object
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1969	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1970	An <a class="link" href="#def_object">object</a> which contains the information about a
				1971	particular <a class="link" href="#def_revision">revision</a>, such as <a class="link" href="#def_parent">parents</a>, committer,
				1972	author, date and the <a class="link" href="#def_tree_object">tree object</a> which corresponds
				1973	to the top <a class="link" href="#def_directory">directory</a> of the stored
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	1974	revision.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1975	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1976	<a name="def_core_git"></a>core git
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1977	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1978	Fundamental data structures and utilities of git. Exposes only limited
				1979	source code management tools.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1980	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1981	<a name="def_DAG"></a>DAG
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1982	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1983	Directed acyclic graph. The <a class="link" href="#def_commit_object">commit objects</a> form a
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1984	directed acyclic graph, because they have parents (directed), and the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1985	graph of commit objects is acyclic (there is no <a class="link" href="#def_chain">chain</a>
				1986	which begins and ends with the same <a class="link" href="#def_object">object</a>).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	1987	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	1988	<a name="def_dangling_object"></a>dangling object
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	1989	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1990	An <a class="link" href="#def_unreachable_object">unreachable object</a> which is not
				1991	<a class="link" href="#def_reachable">reachable</a> even from other unreachable objects; a
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1992	dangling object has no references to it from any
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1993	reference or <a class="link" href="#def_object">object</a> in the <a class="link" href="#def_repository">repository</a>.
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	1994	</dd><dt><span class="term">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	1995	<a name="def_detached_HEAD"></a>detached HEAD
				1996	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	1997	Normally the <a class="link" href="#def_HEAD">HEAD</a> stores the name of a
				1998	<a class="link" href="#def_branch">branch</a>. However, git also allows you to <a class="link" href="#def_checkout">check out</a>
				1999	an arbitrary <a class="link" href="#def_commit">commit</a> that isn't necessarily the tip of any
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2000	particular branch. In this case HEAD is said to be "detached".
				2001	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2002	<a name="def_dircache"></a>dircache
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2003	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2004	You are <span class="strong"><strong>waaaaay</strong></span> behind. See <a class="link" href="#def_index">index</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2005	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2006	<a name="def_directory"></a>directory
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2007	</span></dt><dd>
				2008	The list you get with "ls" :-)
				2009	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2010	<a name="def_dirty"></a>dirty
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2011	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2012	A <a class="link" href="#def_working_tree">working tree</a> is said to be "dirty" if
				2013	it contains modifications which have not been <a class="link" href="#def_commit">committed</a> to the current
				2014	<a class="link" href="#def_branch">branch</a>.
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2015	</dd><dt><span class="term">
				2016	<a name="def_ent"></a>ent
				2017	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2018	Favorite synonym to "<a class="link" href="#def_tree-ish">tree-ish</a>" by some total geeks. See
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2019	<code class="literal">http://en.wikipedia.org/wiki/Ent_(Middle-earth)</code> for an in-depth
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2020	explanation. Avoid this term, not to confuse people.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2021	</dd><dt><span class="term">
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2022	<a name="def_evil_merge"></a>evil merge
				2023	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2024	An evil merge is a <a class="link" href="#def_merge">merge</a> that introduces changes that
				2025	do not appear in any <a class="link" href="#def_parent">parent</a>.
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2026	</dd><dt><span class="term">
Junio C Hamano	3f680f3	2009-11-16 02:10:54	[diff] [blame]	2027	<a name="def_fast_forward"></a>fast-forward
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2028	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2029	A fast-forward is a special type of <a class="link" href="#def_merge">merge</a> where you have a
				2030	<a class="link" href="#def_revision">revision</a> and you are "merging" another
				2031	<a class="link" href="#def_branch">branch</a>'s changes that happen to be a descendant of what
				2032	you have. In such these cases, you do not make a new <a class="link" href="#def_merge">merge</a>
				2033	<a class="link" href="#def_commit">commit</a> but instead just update to his
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2034	revision. This will happen frequently on a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2035	<a class="link" href="#def_tracking_branch">tracking branch</a> of a remote
				2036	<a class="link" href="#def_repository">repository</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2037	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2038	<a name="def_fetch"></a>fetch
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2039	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2040	Fetching a <a class="link" href="#def_branch">branch</a> means to get the
				2041	branch's <a class="link" href="#def_head_ref">head ref</a> from a remote
				2042	<a class="link" href="#def_repository">repository</a>, to find out which objects are
				2043	missing from the local <a class="link" href="#def_object_database">object database</a>,
				2044	and to get them, too. See also <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2045	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2046	<a name="def_file_system"></a>file system
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2047	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2048	Linus Torvalds originally designed git to be a user space file system,
				2049	i.e. the infrastructure to hold files and directories. That ensured the
				2050	efficiency and speed of git.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2051	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2052	<a name="def_git_archive"></a>git archive
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2053	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2054	Synonym for <a class="link" href="#def_repository">repository</a> (for arch people).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2055	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2056	<a name="def_grafts"></a>grafts
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2057	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2058	Grafts enables two otherwise different lines of development to be joined
				2059	together by recording fake ancestry information for commits. This way
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2060	you can make git pretend the set of <a class="link" href="#def_parent">parents</a> a <a class="link" href="#def_commit">commit</a> has
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2061	is different from what was recorded when the commit was
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2062	created. Configured via the <code class="literal">.git/info/grafts</code> file.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2063	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2064	<a name="def_hash"></a>hash
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2065	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2066	In git's context, synonym to <a class="link" href="#def_object_name">object name</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2067	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2068	<a name="def_head"></a>head
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2069	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2070	A <a class="link" href="#def_ref">named reference</a> to the <a class="link" href="#def_commit">commit</a> at the tip of a
				2071	<a class="link" href="#def_branch">branch</a>. Heads are stored in
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2072	<code class="literal">$GIT_DIR/refs/heads/</code>, except when using packed refs. (See
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2073	<a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>.)
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2074	</dd><dt><span class="term">
				2075	<a name="def_HEAD"></a>HEAD
				2076	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2077	The current <a class="link" href="#def_branch">branch</a>. In more detail: Your <a class="link" href="#def_working_tree">working tree</a> is normally derived from the state of the tree
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2078	referred to by HEAD. HEAD is a reference to one of the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2079	<a class="link" href="#def_head">heads</a> in your repository, except when using a
				2080	<a class="link" href="#def_detached_HEAD">detached HEAD</a>, in which case it may
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2081	reference an arbitrary commit.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2082	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2083	<a name="def_head_ref"></a>head ref
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2084	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2085	A synonym for <a class="link" href="#def_head">head</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2086	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2087	<a name="def_hook"></a>hook
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2088	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2089	During the normal execution of several git commands, call-outs are made
				2090	to optional scripts that allow a developer to add functionality or
				2091	checking. Typically, the hooks allow for a command to be pre-verified
				2092	and potentially aborted, and allow for a post-notification after the
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2093	operation is done. The hook scripts are found in the
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2094	<code class="literal">$GIT_DIR/hooks/</code> directory, and are enabled by simply
Junio C Hamano	116db35	2008-12-17 19:48:40	[diff] [blame]	2095	removing the <code class="literal">.sample</code> suffix from the filename. In earlier versions
				2096	of git you had to make them executable.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2097	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2098	<a name="def_index"></a>index
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2099	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2100	A collection of files with stat information, whose contents are stored
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2101	as objects. The index is a stored version of your
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2102	<a class="link" href="#def_working_tree">working tree</a>. Truth be told, it can also contain a second, and even
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2103	a third version of a working tree, which are used
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2104	when <a class="link" href="#def_merge">merging</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2105	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2106	<a name="def_index_entry"></a>index entry
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2107	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2108	The information regarding a particular file, stored in the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2109	<a class="link" href="#def_index">index</a>. An index entry can be unmerged, if a
				2110	<a class="link" href="#def_merge">merge</a> was started, but not yet finished (i.e. if
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2111	the index contains multiple versions of that file).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2112	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2113	<a name="def_master"></a>master
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2114	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2115	The default development <a class="link" href="#def_branch">branch</a>. Whenever you
				2116	create a git <a class="link" href="#def_repository">repository</a>, a branch named
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2117	"master" is created, and becomes the active branch. In most
				2118	cases, this contains the local development, though that is
				2119	purely by convention and is not required.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2120	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2121	<a name="def_merge"></a>merge
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2122	</span></dt><dd><p class="simpara">
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2123	As a verb: To bring the contents of another
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2124	<a class="link" href="#def_branch">branch</a> (possibly from an external
				2125	<a class="link" href="#def_repository">repository</a>) into the current branch. In the
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2126	case where the merged-in branch is from a different repository,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2127	this is done by first <a class="link" href="#def_fetch">fetching</a> the remote branch
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2128	and then merging the result into the current branch. This
				2129	combination of fetch and merge operations is called a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2130	<a class="link" href="#def_pull">pull</a>. Merging is performed by an automatic process
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2131	that identifies changes made since the branches diverged, and
				2132	then applies all those changes together. In cases where changes
				2133	conflict, manual intervention may be required to complete the
				2134	merge.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2135	</p><p class="simpara">As a noun: unless it is a <a class="link" href="#def_fast_forward">fast-forward</a>, a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2136	successful merge results in the creation of a new <a class="link" href="#def_commit">commit</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2137	representing the result of the merge, and having as
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2138	<a class="link" href="#def_parent">parents</a> the tips of the merged <a class="link" href="#def_branch">branches</a>.
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2139	This commit is referred to as a "merge commit", or sometimes just a
				2140	"merge".</p></dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2141	<a name="def_object"></a>object
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2142	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2143	The unit of storage in git. It is uniquely identified by the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2144	<a class="link" href="#def_SHA1">SHA1</a> of its contents. Consequently, an
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2145	object can not be changed.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2146	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2147	<a name="def_object_database"></a>object database
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2148	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2149	Stores a set of "objects", and an individual <a class="link" href="#def_object">object</a> is
				2150	identified by its <a class="link" href="#def_object_name">object name</a>. The objects usually
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2151	live in <code class="literal">$GIT_DIR/objects/</code>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2152	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2153	<a name="def_object_identifier"></a>object identifier
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2154	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2155	Synonym for <a class="link" href="#def_object_name">object name</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2156	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2157	<a name="def_object_name"></a>object name
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2158	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2159	The unique identifier of an <a class="link" href="#def_object">object</a>. The <a class="link" href="#def_hash">hash</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2160	of the object's contents using the Secure Hash Algorithm
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2161	1 and usually represented by the 40 character hexadecimal encoding of
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2162	the <a class="link" href="#def_hash">hash</a> of the object.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2163	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2164	<a name="def_object_type"></a>object type
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2165	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2166	One of the identifiers "<a class="link" href="#def_commit_object">commit</a>",
				2167	"<a class="link" href="#def_tree_object">tree</a>", "<a class="link" href="#def_tag_object">tag</a>" or
				2168	"<a class="link" href="#def_blob_object">blob</a>" describing the type of an
				2169	<a class="link" href="#def_object">object</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2170	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2171	<a name="def_octopus"></a>octopus
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2172	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2173	To <a class="link" href="#def_merge">merge</a> more than two <a class="link" href="#def_branch">branches</a>. Also denotes an
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2174	intelligent predator.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2175	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2176	<a name="def_origin"></a>origin
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2177	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2178	The default upstream <a class="link" href="#def_repository">repository</a>. Most projects have
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2179	at least one upstream project which they track. By default
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2180	<span class="emphasis"><em>origin</em></span> is used for that purpose. New upstream updates
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2181	will be fetched into remote <a class="link" href="#def_tracking_branch">tracking branches</a> named
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2182	origin/name-of-upstream-branch, which you can see using
Junio C Hamano	ea82cff	2009-03-18 01:54:48	[diff] [blame]	2183	<code class="literal">git branch -r</code>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2184	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2185	<a name="def_pack"></a>pack
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2186	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2187	A set of objects which have been compressed into one file (to save space
				2188	or to transmit them efficiently).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2189	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2190	<a name="def_pack_index"></a>pack index
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2191	</span></dt><dd>
				2192	The list of identifiers, and other information, of the objects in a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2193	<a class="link" href="#def_pack">pack</a>, to assist in efficiently accessing the contents of a
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2194	pack.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2195	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2196	<a name="def_parent"></a>parent
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2197	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2198	A <a class="link" href="#def_commit_object">commit object</a> contains a (possibly empty) list
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2199	of the logical predecessor(s) in the line of development, i.e. its
				2200	parents.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2201	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2202	<a name="def_pickaxe"></a>pickaxe
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2203	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2204	The term <a class="link" href="#def_pickaxe">pickaxe</a> refers to an option to the diffcore
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2205	routines that help select changes that add or delete a given text
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	2206	string. With the <code class="literal">—pickaxe-all</code> option, it can be used to view the full
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2207	<a class="link" href="#def_changeset">changeset</a> that introduced or removed, say, a
				2208	particular line of text. See <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2209	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2210	<a name="def_plumbing"></a>plumbing
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2211	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2212	Cute name for <a class="link" href="#def_core_git">core git</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2213	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2214	<a name="def_porcelain"></a>porcelain
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2215	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2216	Cute name for programs and program suites depending on
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2217	<a class="link" href="#def_core_git">core git</a>, presenting a high level access to
				2218	core git. Porcelains expose more of a <a class="link" href="#def_SCM">SCM</a>
				2219	interface than the <a class="link" href="#def_plumbing">plumbing</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2220	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2221	<a name="def_pull"></a>pull
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2222	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2223	Pulling a <a class="link" href="#def_branch">branch</a> means to <a class="link" href="#def_fetch">fetch</a> it and
				2224	<a class="link" href="#def_merge">merge</a> it. See also <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2225	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2226	<a name="def_push"></a>push
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2227	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2228	Pushing a <a class="link" href="#def_branch">branch</a> means to get the branch's
				2229	<a class="link" href="#def_head_ref">head ref</a> from a remote <a class="link" href="#def_repository">repository</a>,
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	2230	find out if it is a direct ancestor to the branch's local
				2231	head ref, and in that case, putting all
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2232	objects, which are <a class="link" href="#def_reachable">reachable</a> from the local
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2233	head ref, and which are missing from the remote
				2234	repository, into the remote
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2235	<a class="link" href="#def_object_database">object database</a>, and updating the remote
				2236	head ref. If the remote <a class="link" href="#def_head">head</a> is not an
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2237	ancestor to the local head, the push fails.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2238	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2239	<a name="def_reachable"></a>reachable
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2240	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2241	All of the ancestors of a given <a class="link" href="#def_commit">commit</a> are said to be
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2242	"reachable" from that commit. More
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2243	generally, one <a class="link" href="#def_object">object</a> is reachable from
				2244	another if we can reach the one from the other by a <a class="link" href="#def_chain">chain</a>
				2245	that follows <a class="link" href="#def_tag">tags</a> to whatever they tag,
				2246	<a class="link" href="#def_commit_object">commits</a> to their parents or trees, and
				2247	<a class="link" href="#def_tree_object">trees</a> to the trees or <a class="link" href="#def_blob_object">blobs</a>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2248	that they contain.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2249	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2250	<a name="def_rebase"></a>rebase
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2251	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2252	To reapply a series of changes from a <a class="link" href="#def_branch">branch</a> to a
				2253	different base, and reset the <a class="link" href="#def_head">head</a> of that branch
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2254	to the result.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2255	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2256	<a name="def_ref"></a>ref
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2257	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2258	A 40-byte hex representation of a <a class="link" href="#def_SHA1">SHA1</a> or a name that
				2259	denotes a particular <a class="link" href="#def_object">object</a>. These may be stored in
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2260	<code class="literal">$GIT_DIR/refs/</code>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2261	</dd><dt><span class="term">
Junio C Hamano	bb0f404	2007-07-04 06:41:40	[diff] [blame]	2262	<a name="def_reflog"></a>reflog
				2263	</span></dt><dd>
				2264	A reflog shows the local "history" of a ref. In other words,
Junio C Hamano	7d3275e	2009-05-31 21:53:30	[diff] [blame]	2265	it can tell you what the 3rd last revision in _this_ repository
				2266	was, and what was the current state in _this_ repository,
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2267	yesterday 9:14pm. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> for details.
Junio C Hamano	bb0f404	2007-07-04 06:41:40	[diff] [blame]	2268	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2269	<a name="def_refspec"></a>refspec
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2270	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2271	A "refspec" is used by <a class="link" href="#def_fetch">fetch</a> and
				2272	<a class="link" href="#def_push">push</a> to describe the mapping between remote
				2273	<a class="link" href="#def_ref">ref</a> and local ref. They are combined with a colon in
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2274	the format <src>:<dst>, preceded by an optional plus sign, +.
				2275	For example: <code class="literal">git fetch $URL
				2276	refs/heads/master:refs/heads/origin</code> means "grab the master
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2277	<a class="link" href="#def_branch">branch</a> <a class="link" href="#def_head">head</a> from the $URL and store
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2278	it as my origin branch head". And <code class="literal">git push
				2279	$URL refs/heads/master:refs/heads/to-upstream</code> means "publish my
				2280	master branch head as to-upstream branch at $URL". See also
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2281	<a class="ulink" href="git-push.html" target="_top">git-push(1)</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2282	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2283	<a name="def_repository"></a>repository
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2284	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2285	A collection of <a class="link" href="#def_ref">refs</a> together with an
				2286	<a class="link" href="#def_object_database">object database</a> containing all objects
				2287	which are <a class="link" href="#def_reachable">reachable</a> from the refs, possibly
				2288	accompanied by meta data from one or more <a class="link" href="#def_porcelain">porcelains</a>. A
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2289	repository can share an object database with other repositories
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2290	via <a class="link" href="#def_alternate_object_database">alternates mechanism</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2291	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2292	<a name="def_resolve"></a>resolve
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2293	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2294	The action of fixing up manually what a failed automatic
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2295	<a class="link" href="#def_merge">merge</a> left behind.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2296	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2297	<a name="def_revision"></a>revision
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2298	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2299	A particular state of files and directories which was stored in the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2300	<a class="link" href="#def_object_database">object database</a>. It is referenced by a
				2301	<a class="link" href="#def_commit_object">commit object</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2302	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2303	<a name="def_rewind"></a>rewind
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2304	</span></dt><dd>
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2305	To throw away part of the development, i.e. to assign the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2306	<a class="link" href="#def_head">head</a> to an earlier <a class="link" href="#def_revision">revision</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2307	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2308	<a name="def_SCM"></a>SCM
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2309	</span></dt><dd>
				2310	Source code management (tool).
				2311	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2312	<a name="def_SHA1"></a>SHA1
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2313	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2314	Synonym for <a class="link" href="#def_object_name">object name</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2315	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2316	<a name="def_shallow_repository"></a>shallow repository
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2317	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2318	A shallow <a class="link" href="#def_repository">repository</a> has an incomplete
				2319	history some of whose <a class="link" href="#def_commit">commits</a> have <a class="link" href="#def_parent">parents</a> cauterized away (in other
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2320	words, git is told to pretend that these commits do not have the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2321	parents, even though they are recorded in the <a class="link" href="#def_commit_object">commit object</a>). This is sometimes useful when you are interested only in the
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2322	recent history of a project even though the real history recorded in the
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2323	upstream is much larger. A shallow repository
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2324	is created by giving the <code class="literal">—depth</code> option to <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a>, and
				2325	its history can be later deepened with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2326	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2327	<a name="def_symref"></a>symref
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2328	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2329	Symbolic reference: instead of containing the <a class="link" href="#def_SHA1">SHA1</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2330	id itself, it is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when
				2331	referenced, it recursively dereferences to this reference.
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2332	<span class="emphasis"><em><a class="link" href="#def_HEAD">HEAD</a></em></span> is a prime example of a symref. Symbolic
				2333	references are manipulated with the <a class="ulink" href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2334	command.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2335	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2336	<a name="def_tag"></a>tag
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2337	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2338	A <a class="link" href="#def_ref">ref</a> pointing to a <a class="link" href="#def_tag_object">tag</a> or
				2339	<a class="link" href="#def_commit_object">commit object</a>. In contrast to a <a class="link" href="#def_head">head</a>,
				2340	a tag is not changed by a <a class="link" href="#def_commit">commit</a>. Tags (not
				2341	<a class="link" href="#def_tag_object">tag objects</a>) are stored in <code class="literal">$GIT_DIR/refs/tags/</code>. A
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2342	git tag has nothing to do with a Lisp tag (which would be
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2343	called an <a class="link" href="#def_object_type">object type</a> in git's context). A
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2344	tag is most typically used to mark a particular point in the
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2345	commit ancestry <a class="link" href="#def_chain">chain</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2346	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2347	<a name="def_tag_object"></a>tag object
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2348	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2349	An <a class="link" href="#def_object">object</a> containing a <a class="link" href="#def_ref">ref</a> pointing to
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2350	another object, which can contain a message just like a
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2351	<a class="link" href="#def_commit_object">commit object</a>. It can also contain a (PGP)
Junio C Hamano	3646098	2007-05-27 04:29:12	[diff] [blame]	2352	signature, in which case it is called a "signed tag object".
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2353	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2354	<a name="def_topic_branch"></a>topic branch
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2355	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2356	A regular git <a class="link" href="#def_branch">branch</a> that is used by a developer to
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2357	identify a conceptual line of development. Since branches are very easy
				2358	and inexpensive, it is often desirable to have several small branches
				2359	that each contain very well defined concepts or small incremental yet
				2360	related changes.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2361	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2362	<a name="def_tracking_branch"></a>tracking branch
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2363	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2364	A regular git <a class="link" href="#def_branch">branch</a> that is used to follow changes from
				2365	another <a class="link" href="#def_repository">repository</a>. A tracking
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2366	branch should not contain direct modifications or have local commits
				2367	made to it. A tracking branch can usually be
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2368	identified as the right-hand-side <a class="link" href="#def_ref">ref</a> in a Pull:
				2369	<a class="link" href="#def_refspec">refspec</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2370	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2371	<a name="def_tree"></a>tree
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2372	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2373	Either a <a class="link" href="#def_working_tree">working tree</a>, or a <a class="link" href="#def_tree_object">tree object</a> together with the dependent <a class="link" href="#def_blob_object">blob</a> and tree objects
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2374	(i.e. a stored representation of a working tree).
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2375	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2376	<a name="def_tree_object"></a>tree object
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2377	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2378	An <a class="link" href="#def_object">object</a> containing a list of file names and modes along
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2379	with refs to the associated blob and/or tree objects. A
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2380	<a class="link" href="#def_tree">tree</a> is equivalent to a <a class="link" href="#def_directory">directory</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2381	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2382	<a name="def_tree-ish"></a>tree-ish
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2383	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2384	A <a class="link" href="#def_ref">ref</a> pointing to either a <a class="link" href="#def_commit_object">commit object</a>, a <a class="link" href="#def_tree_object">tree object</a>, or a <a class="link" href="#def_tag_object">tag object</a> pointing to a tag or commit or tree object.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2385	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2386	<a name="def_unmerged_index"></a>unmerged index
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2387	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2388	An <a class="link" href="#def_index">index</a> which contains unmerged
				2389	<a class="link" href="#def_index_entry">index entries</a>.
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2390	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2391	<a name="def_unreachable_object"></a>unreachable object
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	2392	</span></dt><dd>
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2393	An <a class="link" href="#def_object">object</a> which is not <a class="link" href="#def_reachable">reachable</a> from a
				2394	<a class="link" href="#def_branch">branch</a>, <a class="link" href="#def_tag">tag</a>, or any other reference.
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	2395	</dd><dt><span class="term">
Junio C Hamano	98e32c3	2009-04-13 02:39:53	[diff] [blame]	2396	<a name="def_upstream_branch"></a>upstream branch
				2397	</span></dt><dd>
				2398	The default <a class="link" href="#def_branch">branch</a> that is merged into the branch in
				2399	question (or the branch in question is rebased onto). It is configured
				2400	via branch.<name>.remote and branch.<name>.merge. If the upstream branch
				2401	of <span class="emphasis"><em>A</em></span> is <span class="emphasis"><em>origin/B</em></span> sometimes we say "<span class="emphasis"><em>A</em></span> is tracking <span class="emphasis"><em>origin/B</em></span>".
				2402	</dd><dt><span class="term">
Junio C Hamano	3d5b41f	2007-03-26 02:33:41	[diff] [blame]	2403	<a name="def_working_tree"></a>working tree
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2404	</span></dt><dd>
Junio C Hamano	c0e55e7	2009-10-10 00:56:29	[diff] [blame]	2405	The tree of actual checked out files. The working tree normally
				2406	contains the contents of the <a class="link" href="#def_HEAD">HEAD</a> commit's tree,
				2407	plus any local changes that you have made but not yet committed.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2408	</dd></dl></div></div><div class="appendix" title="Appendix A. Git Quick Reference"><div class="titlepage"><div><div><h2 class="title"><a name="git-quick-start"></a>Appendix A. Git Quick Reference</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></div><p>This is a quick summary of the major commands; the previous chapters
				2409	explain how these work in more detail.</p><div class="section" title="Creating a new repository"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="quick-creating-a-new-repository"></a>Creating a new repository</h2></div></div></div><p>From a tarball:</p><div class="literallayout"><p>$ tar xzf project.tar.gz<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2410	$ cd project<br>
				2411	$ git init<br>
				2412	Initialized empty Git repository in .git/<br>
				2413	$ git add .<br>
				2414	$ git commit</p></div><p>From a remote repository:</p><div class="literallayout"><p>$ git clone git://example.com/pub/project.git<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2415	$ cd project</p></div></div><div class="section" title="Managing branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="managing-branches"></a>Managing branches</h2></div></div></div><div class="literallayout"><p>$ git branch # list all local branches in this repo<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2416	$ git checkout test # switch working directory to branch "test"<br>
				2417	$ git branch new # create branch "new" starting at current HEAD<br>
Junio C Hamano	764a667	2007-10-23 01:23:31	[diff] [blame]	2418	$ git branch -d new # delete branch "new"</p></div><p>Instead of basing a new branch on current HEAD (the default), use:</p><div class="literallayout"><p>$ git branch new test # branch named "test"<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2419	$ git branch new v2.6.15 # tag named v2.6.15<br>
				2420	$ git branch new HEAD^ # commit before the most recent<br>
				2421	$ git branch new HEAD^^ # commit before that<br>
				2422	$ git branch new test~10 # ten commits before tip of branch "test"</p></div><p>Create and switch to a new branch at the same time:</p><div class="literallayout"><p>$ git checkout -b new v2.6.15</p></div><p>Update and examine branches from the repository you cloned from:</p><div class="literallayout"><p>$ git fetch # update<br>
				2423	$ git branch -r # list<br>
				2424	origin/master<br>
				2425	origin/next<br>
				2426	...<br>
				2427	$ git checkout -b masterwork origin/master</p></div><p>Fetch a branch from a different repository, and give it a new
				2428	name in your repository:</p><div class="literallayout"><p>$ git fetch git://example.com/project.git theirbranch:mybranch<br>
				2429	$ git fetch git://example.com/project.git v2.6.15:mybranch</p></div><p>Keep a list of repositories you work with regularly:</p><div class="literallayout"><p>$ git remote add example git://example.com/project.git<br>
				2430	$ git remote # list remote repositories<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2431	example<br>
				2432	origin<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2433	$ git remote show example # get details<br>
				2434	* remote example<br>
				2435	URL: git://example.com/project.git<br>
				2436	Tracked remote branches<br>
Junio C Hamano	edc174c	2008-10-23 05:18:54	[diff] [blame]	2437	master<br>
				2438	next<br>
				2439	...<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2440	$ git fetch example # update branches from example<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2441	$ git branch -r # list all remote branches</p></div></div><div class="section" title="Exploring history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exploring-history"></a>Exploring history</h2></div></div></div><div class="literallayout"><p>$ gitk # visualize and browse history<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2442	$ git log # list all commits<br>
				2443	$ git log src/ # ...modifying src/<br>
				2444	$ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15<br>
				2445	$ git log master..test # ...in branch test, not in branch master<br>
				2446	$ git log test..master # ...in branch master, but not in test<br>
				2447	$ git log test...master # ...in one branch, not in both<br>
				2448	$ git log -S'foo()' # ...where difference contain "foo()"<br>
				2449	$ git log --since="2 weeks ago"<br>
				2450	$ git log -p # show patches as well<br>
				2451	$ git show # most recent commit<br>
				2452	$ git diff v2.6.15..v2.6.16 # diff between two tagged versions<br>
				2453	$ git diff v2.6.15..HEAD # diff with current head<br>
				2454	$ git grep "foo()" # search working directory for "foo()"<br>
				2455	$ git grep v2.6.15 "foo()" # search old tree for "foo()"<br>
				2456	$ git show v2.6.15:a.txt # look at old version of a.txt</p></div><p>Search for regressions:</p><div class="literallayout"><p>$ git bisect start<br>
				2457	$ git bisect bad # current version is bad<br>
				2458	$ git bisect good v2.6.13-rc2 # last known good revision<br>
				2459	Bisecting: 675 revisions left to test after this<br>
				2460	# test here, then:<br>
				2461	$ git bisect good # if this revision is good, or<br>
				2462	$ git bisect bad # if this revision is bad.<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2463	# repeat until done.</p></div></div><div class="section" title="Making changes"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="making-changes"></a>Making changes</h2></div></div></div><p>Make sure git knows who to blame:</p><div class="literallayout"><p>$ cat >>~/.gitconfig <<\EOF<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2464	[user]<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2465	name = Your Name Comes Here<br>
				2466	email = you@yourdomain.example.com<br>
Junio C Hamano	75485c8	2007-05-19 04:20:33	[diff] [blame]	2467	EOF</p></div><p>Select file contents to include in the next commit, then make the
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2468	commit:</p><div class="literallayout"><p>$ git add a.txt # updated file<br>
				2469	$ git add b.txt # new file<br>
				2470	$ git rm c.txt # old file<br>
				2471	$ git commit</p></div><p>Or, prepare and create the commit in one step:</p><div class="literallayout"><p>$ git commit d.txt # use latest content only of d.txt<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2472	$ git commit -a # use latest content of all tracked files</p></div></div><div class="section" title="Merging"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging"></a>Merging</h2></div></div></div><div class="literallayout"><p>$ git merge test # merge branch "test" into the current branch<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2473	$ git pull git://example.com/project.git master<br>
				2474	# fetch and merge in remote branch<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2475	$ git pull . test # equivalent to git merge test</p></div></div><div class="section" title="Sharing your changes"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-your-changes"></a>Sharing your changes</h2></div></div></div><p>Importing or exporting patches:</p><div class="literallayout"><p>$ git format-patch origin..HEAD # format a patch for each commit<br>
Junio C Hamano	cc13f55	2007-07-24 08:59:43	[diff] [blame]	2476	# in HEAD but not in origin<br>
				2477	$ git am mbox # import patches from the mailbox "mbox"</p></div><p>Fetch a branch in a different git repository, then merge into the
				2478	current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch</p></div><p>Store the fetched branch into a local branch before merging into the
				2479	current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch:mybranch</p></div><p>After creating commits on a local branch, update the remote
				2480	branch with your commits:</p><div class="literallayout"><p>$ git push ssh://example.com/project.git mybranch:theirbranch</p></div><p>When remote and local branch are both named "test":</p><div class="literallayout"><p>$ git push ssh://example.com/project.git test</p></div><p>Shortcut version for a frequently used remote repository:</p><div class="literallayout"><p>$ git remote add example ssh://example.com/project.git<br>
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2481	$ git push example test</p></div></div><div class="section" title="Repository maintenance"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="repository-maintenance"></a>Repository maintenance</h2></div></div></div><p>Check for corruption:</p><div class="literallayout"><p>$ git fsck</p></div><p>Recompress, remove unused cruft:</p><div class="literallayout"><p>$ git gc</p></div></div></div><div class="appendix" title="Appendix B. Notes and todo list for this manual"><div class="titlepage"><div><div><h2 class="title"><a name="todo"></a>Appendix B. Notes and todo list for this manual</h2></div></div></div><p>This is a work in progress.</p><p>The basic requirements:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2482	It must be readable in order, from beginning to end, by someone
				2483	intelligent with a basic grasp of the UNIX command line, but without
				2484	any special knowledge of git. If necessary, any other prerequisites
				2485	should be specifically mentioned as they arise.
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2486	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2487	Whenever possible, section headings should clearly describe the task
				2488	they explain how to do, in language that requires no more knowledge
				2489	than necessary: for example, "importing patches into a project" rather
Junio C Hamano	5f9a6f0	2009-04-06 08:26:56	[diff] [blame]	2490	than "the <code class="literal">git am</code> command"
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2491	</li></ul></div><p>Think about how to create a clear chapter dependency graph that will
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2492	allow people to get to important topics without necessarily reading
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2493	everything in between.</p><p>Scan Documentation/ for other stuff left out; in particular:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2494	howto's
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2495	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2496	some of technical/?
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2497	</li><li class="listitem">
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2498	hooks
Junio C Hamano	281025e	2009-12-03 02:47:42	[diff] [blame]	2499	</li><li class="listitem">
Junio C Hamano	ba4b928	2008-07-06 05:20:31	[diff] [blame]	2500	list of commands in <a class="ulink" href="git.html" target="_top">git(1)</a>
Junio C Hamano	597ffcf	2007-09-17 17:33:15	[diff] [blame]	2501	</li></ul></div><p>Scan email archives for other stuff left out</p><p>Scan man pages to see if any assume more background than this manual
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2502	provides.</p><p>Simplify beginning by suggesting disconnected head instead of
Junio C Hamano	aa83a7d	2007-03-05 02:37:29	[diff] [blame]	2503	temporary branch creation?</p><p>Add more good examples. Entire sections of just cookbook examples
Junio C Hamano	8f62db9	2007-02-01 00:22:22	[diff] [blame]	2504	might be a good idea; maybe make an "advanced examples" section a
				2505	standard end-of-chapter section?</p><p>Include cross-references to the glossary, where appropriate.</p><p>Document shallow clones? See draft 1.5.0 release notes for some
Junio C Hamano	ee1e428	2007-02-04 08:32:04	[diff] [blame]	2506	documentation.</p><p>Add a section on working with other version control systems, including
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	2507	CVS, Subversion, and just imports of series of release tarballs.</p><p>More details on gitweb?</p><p>Write a chapter on using plumbing and writing scripts.</p><p>Alternates, clone -reference, etc.</p><p>More on recovery from repository corruption. See:
				2508	http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2
Junio C Hamano	ce3650e	2007-11-26 04:20:11	[diff] [blame]	2509	http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2</p></div></div></body></html>