| <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User's Manual (for version 1.5.1 or newer)</title><link rel="stylesheet" href="docbook-xsl.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.69.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en"><div class="titlepage"><div><div><h1 class="title"><a name="id189136"></a>Git User's Manual (for version 1.5.1 or newer)</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="preface"><a href="#id264725">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></dl></dd><dt><span class="section"><a href="#Finding-comments-with-given-content">Finding commits referencing a file with given content</a></span></dt></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-editing-history">Fixing a mistake by editing history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</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="#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="#modifying-one-commit">Modifying 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></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-internals">7. Git internals</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#commit-object">Commit 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="#the-index">The "index" aka "Current Directory Cache"</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><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="#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">8. 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" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id264725"></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 |
| command-line skills, but no previous knowledge of git.</p><p><a href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a> and <a href="#exploring-git-history" title="Chapter 2. Exploring git history">Chapter 2, <i>Exploring git history</i></a> explain how |
| to fetch and study a project using git—read these chapters to learn how |
| to build and test a particular version of a software project, search for |
| regressions, and so on.</p><p>People needing to do actual development will also want to read |
| <a href="#Developing-with-git" title="Chapter 3. Developing with git">Chapter 3, <i>Developing with git</i></a> and <a 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 |
| pages. For a command such as "git clone", just use</p><div class="literallayout"><p>$ man git-clone</p></div><p>See also <a 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, |
| without any explanation.</p><p>Finally, see <a 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 |
| complete.</p></div><div class="chapter" lang="en"><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" lang="en"><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 |
| read this manual.</p><p>The best way to get one is by using the <a href="git-clone.html" target="_top">git-clone(1)</a> command |
| to download a copy of an existing repository for a project that you |
| are interested in. If you don't already have a project in mind, here |
| are some interesting examples:</p><div class="literallayout"><p> # git itself (approx. 10MB download):<br> |
| $ git clone git://git.kernel.org/pub/scm/git/git.git<br> |
| # the linux kernel (approx. 150MB download):<br> |
| $ 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 |
| will only need to clone once.</p><p>The clone command creates a new directory named after the project |
| ("git" or "linux-2.6" in the examples above). After you cd into this |
| directory, you will see that it contains a copy of the project files, |
| together with a special top-level directory named ".git", which |
| contains all the information about the history of the project.</p><p>In most of the following, examples will be taken from one of the two |
| repositories above.</p></div><div class="section" lang="en"><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 of files. It stores the history as a compressed |
| collection of interrelated snapshots (versions) of the project's |
| contents.</p><p>A single git repository may contain multiple branches. It keeps track |
| of them by keeping a list of <a href="#def_head">heads</a> which reference the |
| latest version on each branch; the <a href="git-branch.html" target="_top">git-branch(1)</a> command shows |
| you the list of branch heads:</p><div class="literallayout"><p>$ git branch<br> |
| * master</p></div><p>A freshly cloned repository contains a single branch head, by default |
| named "master", with the working directory initialized to the state of |
| the project referred to by that branch head.</p><p>Most projects also use <a href="#def_tag">tags</a>. Tags, like heads, are |
| references into the project's history, and can be listed using the |
| <a href="git-tag.html" target="_top">git-tag(1)</a> command:</p><div class="literallayout"><p>$ git tag -l<br> |
| v2.6.11<br> |
| v2.6.11-tree<br> |
| v2.6.12<br> |
| v2.6.12-rc2<br> |
| v2.6.12-rc3<br> |
| v2.6.12-rc4<br> |
| v2.6.12-rc5<br> |
| v2.6.12-rc6<br> |
| v2.6.13<br> |
| ...</p></div><p>Tags are expected to always point at the same version of a project, |
| 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 |
| out using <a 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 |
| when it was tagged v2.6.13, and <a href="git-branch.html" target="_top">git-branch(1)</a> shows two |
| branches, with an asterisk marking the currently checked-out branch:</p><div class="literallayout"><p>$ git branch<br> |
| master<br> |
| * new</p></div><p>If you decide that you'd rather see version 2.6.17, you can modify |
| 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 |
| particular point in history, then resetting that branch may leave you |
| with no way to find the history it used to point to; so use this command |
| carefully.</p></div><div class="section" lang="en"><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. |
| The <a href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the |
| current branch:</p><div class="literallayout"><p>$ git show<br> |
| commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2<br> |
| Author: Jamal Hadi Salim <hadi@cyberus.ca><br> |
| Date: Sat Dec 2 22:22:25 2006 -0800<br> |
| <br> |
| [XFRM]: Fix aevent structuring to be more complete.<br> |
| <br> |
| aevents can not uniquely identify an SA. We break the ABI with this<br> |
| patch, but consensus is that since it is not yet utilized by any<br> |
| (known) application then it is fine (better do it now than later).<br> |
| <br> |
| Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca><br> |
| Signed-off-by: David S. Miller <davem@davemloft.net><br> |
| <br> |
| diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt<br> |
| index 8be626f..d7aac9d 100644<br> |
| --- a/Documentation/networking/xfrm_sync.txt<br> |
| +++ b/Documentation/networking/xfrm_sync.txt<br> |
| @@ -47,10 +47,13 @@ aevent_id structure looks like:<br> |
| <br> |
| struct xfrm_aevent_id {<br> |
| struct xfrm_usersa_id sa_id;<br> |
| + xfrm_address_t saddr;<br> |
| __u32 flags;<br> |
| + __u32 reqid;<br> |
| };<br> |
| ...</p></div><p>As you can see, a commit shows who made the latest change, what they |
| did, and why.</p><p>Every commit has a 40-hexdigit id, sometimes called the "object name" or the |
| "SHA1 id", shown on the first line of the "git show" output. You can usually |
| refer to a commit by a shorter name, such as a tag or a branch name, but this |
| longer name can also be useful. Most importantly, it is a globally unique |
| name for this commit: so if you tell somebody else the object name (for |
| example in email), then you are guaranteed that name will refer to the same |
| commit in their repository that it does in yours (assuming their repository |
| has that commit at all). Since the object name is computed as a hash over the |
| contents of the commit, you are guaranteed that the commit can never change |
| without its name also changing.</p><p>In fact, in <a href="#git-internals" title="Chapter 7. Git internals">Chapter 7, <i>Git internals</i></a> we shall see that everything stored in git |
| history, including file data and directory contents, is stored in an object |
| with a name that is a hash of its contents.</p><div class="section" lang="en"><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 |
| parent commit which shows what happened before this commit. |
| Following the chain of parents will eventually take you back to the |
| beginning of the project.</p><p>However, the commits do not form a simple list; git allows lines of |
| development to diverge and then reconverge, and the point where two |
| lines of development reconverge is called a "merge". The commit |
| representing a merge can therefore have more than one parent, with |
| each parent representing the most recent commit on one of the lines |
| of development leading to that point.</p><p>The best way to see how this works is using the <a href="gitk.html" target="_top">gitk(1)</a> |
| command; running gitk now on a git repository and looking for merge |
| commits will help understand how the git organizes history.</p><p>In the following, we say that commit X is "reachable" from commit Y |
| if commit X is an ancestor of commit Y. Equivalently, you could say |
| that Y is a descendent of X, or that there is a chain of parents |
| leading from commit Y to commit X.</p></div><div class="section" lang="en"><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 |
| below. Commits are shown as "o", and the links between them with |
| lines drawn with - / and \. Time goes left to right:</p><pre class="literallayout"> o--o--o <-- Branch A |
| / |
| o--o--o <-- master |
| \ |
| o--o--o <-- Branch B</pre><p>If we need to talk about a particular commit, the character "o" may |
| be replaced with another letter or number.</p></div><div class="section" lang="en"><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 |
| of development, and "branch head" (or just "head") to mean a reference |
| to the most recent commit on a branch. In the example above, the branch |
| head named "A" is a pointer to one particular commit, but we refer to |
| the line of three commits leading up to that point as all being part of |
| "branch A".</p><p>However, when no confusion will result, we often just use the term |
| "branch" both for branches and for branch heads.</p></div></div><div class="section" lang="en"><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 |
| a summary of the commands:</p><div class="variablelist"><dl><dt><span class="term"> |
| git branch |
| </span></dt><dd> |
| list all branches |
| </dd><dt><span class="term"> |
| git branch <branch> |
| </span></dt><dd> |
| create a new branch named <branch>, referencing the same |
| point in history as the current branch |
| </dd><dt><span class="term"> |
| git branch <branch> <start-point> |
| </span></dt><dd> |
| create a new branch named <branch>, referencing |
| <start-point>, which may be specified any way you like, |
| including using a branch name or a tag name |
| </dd><dt><span class="term"> |
| git branch -d <branch> |
| </span></dt><dd> |
| delete the branch <branch>; if the branch you are deleting |
| points to a commit which is not reachable from the current |
| branch, this command will fail with a warning. |
| </dd><dt><span class="term"> |
| git branch -D <branch> |
| </span></dt><dd> |
| even if the branch points to a commit not reachable |
| from the current branch, you may know that that commit |
| is still reachable from some other branch or tag. In that |
| case it is safe to use this command to force git to delete |
| the branch. |
| </dd><dt><span class="term"> |
| git checkout <branch> |
| </span></dt><dd> |
| make the current branch <branch>, updating the working |
| directory to reflect the version referenced by <branch> |
| </dd><dt><span class="term"> |
| git checkout -b <new> <start-point> |
| </span></dt><dd> |
| create a new branch <new> referencing <start-point>, and |
| check it out. |
| </dd></dl></div><p>The special symbol "HEAD" can always be used to refer to the current |
| branch. In fact, git uses a file named "HEAD" in the .git directory to |
| remember which branch is current:</p><div class="literallayout"><p>$ cat .git/HEAD<br> |
| ref: refs/heads/master</p></div></div><div class="section" lang="en"><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 git-checkout command normally expects a branch head, but will also |
| accept an arbitrary commit; for example, you can check out the commit |
| referenced by a tag:</p><div class="literallayout"><p>$ git checkout v2.6.17<br> |
| Note: moving to "v2.6.17" which isn't a local branch<br> |
| If you want to create a new branch from this checkout, you may do so<br> |
| (now or later) by using -b with the checkout command again. Example:<br> |
| git checkout -b <new_branch_name><br> |
| HEAD is now at 427abfa... Linux v2.6.17</p></div><p>The HEAD then refers to the SHA1 of the commit instead of to a branch, |
| and git branch shows that you are no longer on a branch:</p><div class="literallayout"><p>$ cat .git/HEAD<br> |
| 427abfa28afedffadfca9dd8b067eb6d36bac53f<br> |
| $ git branch<br> |
| * (no branch)<br> |
| 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 |
| make up a name for the new branch. You can still create a new branch |
| (or tag) for this version later if you decide to.</p></div><div class="section" lang="en"><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 |
| of the HEAD in the repository that you cloned from. That repository |
| may also have had other branches, though, and your local repository |
| keeps branches which track each of those remote branches, which you |
| can view using the "-r" option to <a href="git-branch.html" target="_top">git-branch(1)</a>:</p><div class="literallayout"><p>$ git branch -r<br> |
| origin/HEAD<br> |
| origin/html<br> |
| origin/maint<br> |
| origin/man<br> |
| origin/master<br> |
| origin/next<br> |
| origin/pu<br> |
| origin/todo</p></div><p>You cannot check out these remote-tracking branches, but you can |
| 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 |
| to refer to the repository that you cloned from.</p></div><div class="section" lang="en"><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 |
| commits. All references are named with a slash-separated path name |
| starting with "refs"; the names we've been using so far are actually |
| shorthand:</p><div class="itemizedlist"><ul type="disc"><li> |
| The branch "test" is short for "refs/heads/test". |
| </li><li> |
| The tag "v2.6.18" is short for "refs/tags/v2.6.18". |
| </li><li> |
| "origin/master" is short for "refs/remotes/origin/master". |
| </li></ul></div><p>The full name is occasionally useful if, for example, there ever |
| exists a tag and a branch with the same name.</p><p>As another useful shortcut, the "HEAD" of a repository can be referred |
| to just using the name of that repository. So, for example, "origin" |
| 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 |
| the order it uses to decide which to choose when there are multiple |
| references with the same shorthand name, see the "SPECIFYING |
| REVISIONS" section of <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a>.</p></div><div class="section" lang="en"><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 |
| repository, creating new commits and advancing the branches to point |
| at the new commits.</p><p>The command "git fetch", with no arguments, will update all of the |
| remote-tracking branches to the latest version found in her |
| repository. It will not touch any of your own branches—not even the |
| "master" branch that was created for you on clone.</p></div><div class="section" lang="en"><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 |
| cloned from, using <a 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> |
| $ git fetch linux-nfs<br> |
| * refs/remotes/linux-nfs/master: storing branch 'master' ...<br> |
| commit: bf81b46</p></div><p>New remote-tracking branches will be stored under the shorthand name |
| that you gave "git remote add", in this case linux-nfs:</p><div class="literallayout"><p>$ git branch -r<br> |
| linux-nfs/master<br> |
| origin/master</p></div><p>If you run "git fetch <remote>" later, the tracking branches for the |
| named <remote> will be updated.</p><p>If you examine the file .git/config, you will see that git has added |
| a new stanza:</p><div class="literallayout"><p>$ cat .git/config<br> |
| ...<br> |
| [remote "linux-nfs"]<br> |
| url = git://linux-nfs.org/pub/nfs-2.6.git<br> |
| fetch = +refs/heads/*:refs/remotes/linux-nfs/*<br> |
| ...</p></div><p>This is what causes git to track the remote's branches; you may modify |
| or delete these configuration options by editing .git/config with a |
| text editor. (See the "CONFIGURATION FILE" section of |
| <a href="git-config.html" target="_top">git-config(1)</a> for details.)</p></div></div><div class="chapter" lang="en"><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></dl></dd><dt><span class="section"><a href="#Finding-comments-with-given-content">Finding commits referencing a file with given content</a></span></dt></dl></div><p>Git is best thought of as a tool for storing the history of a |
| collection of files. It does this by storing compressed snapshots of |
| the contents of a file hierarchy, together with "commits" which show |
| the relationships between these snapshots.</p><p>Git provides extremely flexible and fast tools for exploring the |
| history of a project.</p><p>We start with one specialized tool that is useful for finding the |
| commit that introduced a bug into a project.</p><div class="section" lang="en"><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 |
| "master" crashes. Sometimes the best way to find the cause of such a |
| regression is to perform a brute-force search through the project's |
| history to find the particular commit that caused the problem. The |
| <a 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> |
| $ git bisect good v2.6.18<br> |
| $ git bisect bad master<br> |
| Bisecting: 3537 revisions left to test after this<br> |
| [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 |
| temporarily moved you to a new branch named "bisect". This branch |
| points to a commit (with commit id 65934…) that is reachable from |
| v2.6.19 but not from v2.6.18. Compile and test it, and see whether |
| it crashes. Assume it does crash. Then:</p><div class="literallayout"><p>$ git bisect bad<br> |
| Bisecting: 1769 revisions left to test after this<br> |
| [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</p></div><p>checks out an older version. Continue like this, telling git at each |
| stage whether the version it gives you is good or bad, and notice |
| that the number of revisions left to test is cut approximately in |
| half each time.</p><p>After about 13 tests (in this case), it will output the commit id of |
| the guilty commit. You can then examine the commit with |
| <a href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug |
| 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 and delete the |
| temporary "bisect" branch.</p><p>Note that the version which git-bisect checks out for you at each |
| point is just a suggestion, and you're free to try a different |
| version if you think it would be a good idea. For example, |
| occasionally you may land on a commit that broke something unrelated; |
| 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 |
| says "bisect". Chose a safe-looking commit nearby, note its commit |
| 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 |
| continue.</p></div><div class="section" lang="en"><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 type="disc"><li> |
| 40-hexdigit object name |
| </li><li> |
| branch name: refers to the commit at the head of the given |
| branch |
| </li><li> |
| tag name: refers to the commit pointed to by the given tag |
| (we've seen branches and tags are special cases of |
| <a href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>). |
| </li><li> |
| HEAD: refers to the head of the current branch |
| </li></ul></div><p>There are many more; see the "SPECIFYING REVISIONS" section of the |
| <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> man page for the complete list of ways to |
| name revisions. Some examples:</p><div class="literallayout"><p>$ git show fb47ddb2 # the first few characters of the object name<br> |
| # are usually enough to specify it uniquely<br> |
| $ git show HEAD^ # the parent of the HEAD commit<br> |
| $ git show HEAD^^ # the grandparent<br> |
| $ git show HEAD~4 # the great-great-grandparent</p></div><p>Recall that merge commits may have more than one parent; by default, |
| ^ and ~ follow the first parent listed in the commit, but you can |
| also choose:</p><div class="literallayout"><p>$ git show HEAD^1 # show the first parent of HEAD<br> |
| $ git show HEAD^2 # show the second parent of HEAD</p></div><p>In addition to HEAD, there are several other special names for |
| commits:</p><p>Merges (to be discussed later), as well as operations such as |
| git-reset, which change the currently checked-out commit, generally |
| set ORIG_HEAD to the value HEAD had before the current operation.</p><p>The git-fetch operation always stores the head of the last fetched |
| branch in FETCH_HEAD. For example, if you run git fetch without |
| 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, |
| which refers to the other branch that we're merging in to the current |
| branch.</p><p>The <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is |
| occasionally useful for translating some name for a commit to the object |
| name for that commit:</p><div class="literallayout"><p>$ git rev-parse origin<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div></div><div class="section" lang="en"><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 |
| 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 |
| comment with the tag, and possibly sign it cryptographically, then you |
| should create a tag object instead; see the <a href="git-tag.html" target="_top">git-tag(1)</a> man page |
| for details.</p></div><div class="section" lang="en"><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 href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its |
| own, it shows all commits reachable from the parent commit; but you |
| can also make more specific requests:</p><div class="literallayout"><p>$ git log v2.5.. # commits since (not reachable from) v2.5<br> |
| $ git log test..master # commits reachable from master but not test<br> |
| $ git log master..test # ...reachable from test but not master<br> |
| $ git log master...test # ...reachable from either test or master,<br> |
| # but not both<br> |
| $ git log --since="2 weeks ago" # commits from the last 2 weeks<br> |
| $ git log Makefile # commits which modify Makefile<br> |
| $ git log fs/ # ... which modify any file under fs/<br> |
| $ git log -S'foo()' # commits which add or remove any file data<br> |
| # matching the string 'foo()'</p></div><p>And of course you can combine all of these; the following finds |
| 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 href="git-log.html" target="_top">git-log(1)</a> man page for more |
| display options.</p><p>Note that git log starts with the most recent commit and works |
| backwards through the parents; however, since git history can contain |
| multiple independent lines of development, the particular order that |
| commits are listed in may be somewhat arbitrary.</p></div><div class="section" lang="en"><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 |
| <a href="git-diff.html" target="_top">git-diff(1)</a>:</p><div class="literallayout"><p>$ git diff master..test</p></div><p>Sometimes what you want instead is a set of patches:</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 |
| but not from master. Note that if master also has commits which are |
| not reachable from test, then the combined result of these patches |
| will not be the same as the diff produced by the git-diff example.</p></div><div class="section" lang="en"><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 |
| correct revision first. But sometimes it is more convenient to be |
| able to view an old version of a single file without checking |
| 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 |
| may be any path to a file tracked by git.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div><div class="section" lang="en"><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" |
| 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 |
| lower-level command <a href="git-rev-list.html" target="_top">git-rev-list(1)</a>, which just lists the SHA1's |
| of all the given commits:</p><div class="literallayout"><p>$ git rev-list origin..mybranch | wc -l</p></div></div><div class="section" lang="en"><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 |
| 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 |
| two branches; in theory, however, it's possible that the same project |
| contents could have been arrived at by two different historical |
| routes. You could compare the object names:</p><div class="literallayout"><p>$ git rev-list origin<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b<br> |
| $ git rev-list master<br> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>Or you could recall that the … operator selects all commits |
| contained reachable from either one reference or the other but not |
| 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" lang="en"><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. |
| You'd like to find the earliest tagged release that contains that |
| fix.</p><p>Of course, there may be more than one answer—if the history branched |
| after commit e05db0fd, then there could be multiple "earliest" tagged |
| 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 href="git-name-rev.html" target="_top">git-name-rev(1)</a>, which will give the commit a |
| name based on any tag it finds pointing to one of the commit's |
| descendants:</p><div class="literallayout"><p>$ git name-rev --tags e05db0fd<br> |
| e05db0fd tags/v1.5.0-rc1^0~23</p></div><p>The <a href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the |
| revision using a tag on which the given commit is based:</p><div class="literallayout"><p>$ git describe e05db0fd<br> |
| v1.5.0-rc0-260-ge05db0f</p></div><p>but that may sometimes help you guess which tags might come after the |
| given commit.</p><p>If you just want to verify whether a given tagged version contains a |
| given commit, you could use <a 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> |
| e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>The merge-base command finds a common ancestor of the given commits, |
| and always returns one or the other in the case where one is a |
| descendant of the other; so the above output shows that e05db0fd |
| 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, |
| because it outputs only commits that are not reachable from v1.5.0-rc1.</p><p>As yet another alternative, the <a href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists |
| the commits reachable from its arguments with a display on the left-hand |
| side that indicates which arguments that commit is reachable from. So, |
| 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> |
| ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br> |
| available<br> |
| ! [v1.5.0-rc0] GIT v1.5.0 preview<br> |
| ! [v1.5.0-rc1] GIT v1.5.0-rc1<br> |
| ! [v1.5.0-rc2] GIT v1.5.0-rc2<br> |
| ...</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> |
| available</p></div><p>Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and |
| from v1.5.0-rc2, but not from v1.5.0-rc0.</p></div><div class="section" lang="en"><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 |
| head named "master" but not from any other head in your repository.</p><p>We can list all the heads in this repository with |
| <a href="git-show-ref.html" target="_top">git-show-ref(1)</a>:</p><div class="literallayout"><p>$ git show-ref --heads<br> |
| bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial<br> |
| db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint<br> |
| a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master<br> |
| 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2<br> |
| 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes</p></div><p>We can get just the branch-head names, and remove "master", with |
| 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> |
| refs/heads/core-tutorial<br> |
| refs/heads/maint<br> |
| refs/heads/tutorial-2<br> |
| refs/heads/tutorial-fixes</p></div><p>And then we can ask to see all the commits reachable from master |
| but not from these other heads:</p><div class="literallayout"><p>$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |<br> |
| grep -v '^refs/heads/master' )</p></div><p>Obviously, endless variations are possible; for example, to see all |
| commits reachable from some head but not from any tag in the repository:</p><div class="literallayout"><p>$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )</p></div><p>(See <a href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> for explanations of commit-selecting |
| syntax such as <code class="literal">—not</code>.)</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div><p>The <a href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from |
| any version of a project; for example:</p><div class="literallayout"><p>$ 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 |
| preceded by "project/".</p><p>If you're releasing a new version of a software project, you may want |
| to simultaneously make a changelog to include in the release |
| announcement.</p><p>Linus Torvalds, for example, makes new kernel releases by tagging them, |
| 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> |
| stable="$1"<br> |
| last="$2"<br> |
| new="$3"<br> |
| echo "# git tag v$new"<br> |
| echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"<br> |
| echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"<br> |
| echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"<br> |
| echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"<br> |
| echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"</p></div><p>and then he just cut-and-pastes the output commands after verifying that |
| they look OK.</p></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Finding-comments-with-given-content"></a>Finding commits referencing a file with given content</h2></div></div></div><p>Somebody hands you a copy of a file, and asks which commits modified a |
| file such that it contained the given content either before or after the |
| commit. You can find out with this:</p><div class="literallayout"><p>$ git log --raw -r --abbrev=40 --pretty=oneline -- filename |<br> |
| grep -B 1 `git hash-object filename`</p></div><p>Figuring out why this works is left as an exercise to the (advanced) |
| student. The <a href="git-log.html" target="_top">git-log(1)</a>, <a href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>, and |
| <a href="git-hash-object.html" target="_top">git-hash-object(1)</a> man pages may prove helpful.</p></div></div><div class="chapter" lang="en"><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-editing-history">Fixing a mistake by editing history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</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" lang="en"><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 |
| easiest way to do so is to make sure the following lines appear in a |
| file named .gitconfig in your home directory:</p><div class="literallayout"><p>[user]<br> |
| name = Your Name Comes Here<br> |
| email = you@yourdomain.example.com</p></div><p>(See the "CONFIGURATION FILE" section of <a href="git-config.html" target="_top">git-config(1)</a> for |
| details on the configuration file.)</p></div><div class="section" lang="en"><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> |
| $ cd project<br> |
| $ 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> |
| $ cd project<br> |
| $ git init<br> |
| $ git add . # include everything below ./ in the first commit:<br> |
| $ git commit</p></div></div><div class="section" lang="en"><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 type="1"><li> |
| Making some changes to the working directory using your |
| favorite editor. |
| </li><li> |
| Telling git about your changes. |
| </li><li> |
| Creating the commit using the content you told git about |
| in step 2. |
| </li></ol></div><p>In practice, you can interleave and repeat steps 1 and 2 as many |
| times as you want: in order to keep track of what you want committed |
| at step 3, git maintains a snapshot of the tree's contents in a |
| special staging area called "the index."</p><p>At the beginning, the content of the index will be identical to |
| that of the HEAD. The command "git diff —cached", which shows |
| the difference between the HEAD and the index, should therefore |
| 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 |
| 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 |
| to the index; further changes to the same file will be ignored unless |
| you run git-add 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 |
| 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 |
| and create a commit, all in one step.</p><p>A number of commands are useful for keeping track of what you're |
| about to commit:</p><div class="literallayout"><p>$ git diff --cached # difference between HEAD and the index; what<br> |
| # would be committed if you ran "commit" now.<br> |
| $ git diff # difference between the index file and your<br> |
| # working directory; changes that would not<br> |
| # be included if you ran "commit" now.<br> |
| $ git diff HEAD # difference between HEAD and working tree; what<br> |
| # would be committed if you ran "commit -a" now.<br> |
| $ git status # a brief per-file summary of the above.</p></div></div><div class="section" lang="en"><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 |
| with a single short (less than 50 character) line summarizing the |
| change, followed by a blank line and then a more thorough |
| description. Tools that turn commits into email, for example, use |
| the first line on the Subject line and the rest of the commit in the |
| body.</p></div><div class="section" lang="en"><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. |
| This typically includes files generated by a build process or temporary |
| backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with git |
| 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 |
| annoying to have these untracked files lying around; e.g. they make |
| "<code class="literal">git add .</code>" and "<code class="literal">git commit -a</code>" practically useless, and they keep |
| showing up in the output of "<code class="literal">git status</code>", etc.</p><p>Git therefore provides "exclude patterns" for telling git which files to |
| actively ignore. Exclude patterns are thoroughly explained in the |
| <a href="gitignore.html" target="_top">gitignore(5)</a> manual page, but the heart of the concept is simply |
| a list of files which git should ignore. Entries in the list may contain |
| globs to specify multiple files, or may be prefixed by "<code class="literal">!</code>" to |
| explicitly include (un-ignore) a previously excluded (ignored) file |
| (i.e. later exclude patterns override earlier ones). The following |
| example should illustrate such patterns:</p><div class="literallayout"><p># Lines starting with '#' are considered comments.<br> |
| # Ignore foo.txt.<br> |
| foo.txt<br> |
| # Ignore (generated) html files,<br> |
| *.html<br> |
| # except foo.html which is maintained by hand.<br> |
| !foo.html<br> |
| # Ignore objects and archives.<br> |
| *.[oa]</p></div><p>The next question is where to put these exclude patterns so that git can |
| find them. Git looks for exclude patterns in the following files:</p><div class="variablelist"><dl><dt><span class="term"> |
| <code class="literal">.gitignore</code> files in your working tree: |
| </span></dt><dd> |
| You may store multiple <code class="literal">.gitignore</code> files at various locations in your |
| working tree. Each <code class="literal">.gitignore</code> file is applied to the directory where |
| it's located, including its subdirectories. Furthermore, the |
| <code class="literal">.gitignore</code> files can be tracked like any other files in your working |
| tree; just do a "<code class="literal">git add .gitignore</code>" and commit. <code class="literal">.gitignore</code> is |
| therefore the right place to put exclude patterns that are meant to |
| be shared between all project participants, such as build output files |
| (e.g. <code class="literal">*.o</code>), etc. |
| </dd><dt><span class="term"> |
| <code class="literal">.git/info/exclude</code> in your repo: |
| </span></dt><dd> |
| Exclude patterns in this file are applied to the working tree as a |
| whole. Since the file is not located in your working tree, it does |
| not follow push/pull/clone like <code class="literal">.gitignore</code> can do. This is therefore |
| the place to put exclude patterns that are local to your copy of the |
| repo (i.e. <span class="emphasis"><em>not</em></span> shared between project participants), such as |
| temporary backup files made by your editor (e.g. <code class="literal">*~</code>), etc. |
| </dd><dt><span class="term"> |
| The file specified by the <code class="literal">core.excludesfile</code> config directive: |
| </span></dt><dd> |
| By setting the <code class="literal">core.excludesfile</code> config directive you can tell git |
| where to find more exclude patterns (see <a href="git-config.html" target="_top">git-config(1)</a> for |
| more information on configuration options). This config directive |
| can be set in the per-repo <code class="literal">.git/config</code> file, in which case the |
| exclude patterns will apply to that repo only. Alternatively, you |
| can set the directive in the global <code class="literal">~/.gitconfig</code> file to apply |
| the exclude pattern to all your git repos. As with the above |
| <code class="literal">.git/info/exclude</code> (and, indeed, with git config directives in |
| general), this directive does not follow push/pull/clone, but remain |
| local to your repo(s). |
| </dd></dl></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>In addition to the above alternatives, there are git commands that can take |
| exclude patterns directly on the command line. See <a href="git-ls-files.html" target="_top">git-ls-files(1)</a> |
| for an example of this.</p></div></div><div class="section" lang="en"><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 |
| <a 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 |
| branch. If there are conflicts—for example, if the same file is |
| modified in two different ways in the remote branch and the local |
| branch—then you are warned; the output may look something like this:</p><div class="literallayout"><p>$ git merge next<br> |
| 100% (4/4) done<br> |
| Auto-merged file.txt<br> |
| CONFLICT (content): Merge conflict in file.txt<br> |
| Automatic merge failed; fix conflicts and then commit the result.</p></div><p>Conflict markers are left in the problematic files, and after |
| you resolve the conflicts manually, you can update the index |
| with the contents and run git commit, as you normally would when |
| creating a new file.</p><p>If you examine the resulting commit using gitk, you will see that it |
| has two parents, one pointing to the top of the current branch, and |
| one to the top of the other branch.</p></div><div class="section" lang="en"><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 |
| the working tree in a special state that gives you all the |
| information you need to help resolve the merge.</p><p>Files with conflicts are marked specially in the index, so until you |
| resolve the problem and update the index, <a href="git-commit.html" target="_top">git-commit(1)</a> will |
| fail:</p><div class="literallayout"><p>$ git commit<br> |
| file.txt: needs merge</p></div><p>Also, <a href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the |
| files with conflicts will have conflict markers added, like this:</p><div class="literallayout"><p><<<<<<< HEAD:file.txt<br> |
| Hello world<br> |
| =======<br> |
| Goodbye<br> |
| >>>>>>> 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> |
| $ git commit</p></div><p>Note that the commit message will already be filled in for you with |
| some information about the merge. Normally you can just use this |
| default message unchanged, but you may add additional commentary of |
| your own if desired.</p><p>The above is all you need to know to resolve a simple merge. But git |
| also provides more information to help resolve conflicts:</p><div class="section" lang="en"><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 |
| already added to the index file, so <a href="git-diff.html" target="_top">git-diff(1)</a> shows only |
| the conflicts. It uses an unusual syntax:</p><div class="literallayout"><p>$ git diff<br> |
| diff --cc file.txt<br> |
| index 802992c,2b60207..0000000<br> |
| --- a/file.txt<br> |
| +++ b/file.txt<br> |
| @@@ -1,1 -1,1 +1,5 @@@<br> |
| ++<<<<<<< HEAD:file.txt<br> |
| +Hello world<br> |
| ++=======<br> |
| + Goodbye<br> |
| ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>Recall that the commit which will be committed after we resolve this |
| conflict will have two parents instead of the usual one: one parent |
| will be HEAD, the tip of the current branch; the other will be the |
| 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 |
| 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> |
| $ git show :2:file.txt # the version from HEAD, but including any<br> |
| # nonconflicting changes from MERGE_HEAD<br> |
| $ git show :3:file.txt # the version from MERGE_HEAD, but including any<br> |
| # nonconflicting changes from HEAD.</p></div><p>Since the stage 2 and stage 3 versions have already been updated with |
| nonconflicting changes, the only remaining differences between them are |
| the important ones; thus <a href="git-diff.html" target="_top">git-diff(1)</a> can use the information in |
| the index to show only those conflicts.</p><p>The diff above shows the differences between the working-tree version of |
| file.txt and the stage 2 and stage 3 versions. So instead of preceding |
| each line by a single "+" or "-", it now uses two columns: the first |
| column is used for differences between the first parent and the working |
| directory copy, and the second for differences between the second parent |
| and the working directory copy. (See the "COMBINED DIFF FORMAT" section |
| of <a 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 |
| index), the diff will look like:</p><div class="literallayout"><p>$ git diff<br> |
| diff --cc file.txt<br> |
| index 802992c,2b60207..0000000<br> |
| --- a/file.txt<br> |
| +++ b/file.txt<br> |
| @@@ -1,1 -1,1 +1,1 @@@<br> |
| - Hello world<br> |
| -Goodbye<br> |
| ++Goodbye world</p></div><p>This shows that our resolved version deleted "Hello world" from the |
| first parent, deleted "Goodbye" from the second parent, and added |
| "Goodbye world", which was previously absent from both.</p><p>Some special diff options allow diffing the working directory against |
| any of these stages:</p><div class="literallayout"><p>$ git diff -1 file.txt # diff against stage 1<br> |
| $ git diff --base file.txt # same as the above<br> |
| $ git diff -2 file.txt # diff against stage 2<br> |
| $ git diff --ours file.txt # same as the above<br> |
| $ git diff -3 file.txt # diff against stage 3<br> |
| $ git diff --theirs file.txt # same as the above.</p></div><p>The <a href="git-log.html" target="_top">git-log(1)</a> and gitk[1] commands also provide special help |
| for merges:</p><div class="literallayout"><p>$ git log --merge<br> |
| $ gitk --merge</p></div><p>These will display all commits which exist only on HEAD or on |
| MERGE_HEAD, and which touch an unmerged file.</p><p>You may also use <a href="git-mergetool.html" target="_top">git-mergetool(1)</a>, which lets you merge the |
| 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 |
| git-diff will (by default) no longer show diffs for that file.</p></div></div><div class="section" lang="en"><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 |
| 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 |
| throw away a commit you have already committed if that commit may |
| itself have been merged into another branch, as doing so may confuse |
| further merges.</p></div><div class="section" lang="en"><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 |
| differently. Normally, a merge results in a merge commit, with two |
| parents, one pointing at each of the two lines of development that |
| were merged.</p><p>However, if the current branch is a descendant of the other—so every |
| commit present in the one is already contained in the other—then git |
| just performs a "fast forward"; the head of the current branch is moved |
| forward to point at the head of the merged-in branch, without any new |
| commits being created.</p></div><div class="section" lang="en"><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 |
| mistake, you can return the entire working tree to the last committed |
| 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 |
| fundamentally different ways to fix the problem:</p><div class="orderedlist"><ol type="1"><li> |
| You can create a new commit that undoes whatever was done |
| by the previous commit. This is the correct thing if your |
| mistake has already been made public. |
| </li><li> |
| You can go back and modify the old commit. You should |
| never do this if you have already made the history public; |
| git does not normally expect the "history" of a project to |
| change, and cannot correctly perform repeated merges from |
| a branch that has had its history changed. |
| </li></ol></div><div class="section" lang="en"><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; |
| just pass the <a href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad |
| 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 |
| 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 |
| intact any changes made since then. If more recent changes overlap |
| with the changes to be reverted, then you will be asked to fix |
| conflicts manually, just as in the case of <a href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="fixing-a-mistake-by-editing-history"></a>Fixing a mistake by editing history</h3></div></div></div><p>If the problematic commit is the most recent commit, and you have not |
| yet made that commit public, then you may just |
| <a href="#undoing-a-merge" title="Undoing a merge">destroy it using git-reset</a>.</p><p>Alternatively, you |
| can edit the working directory and update the index to fix your |
| mistake, just as if you were going to <a 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 |
| 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 |
| been merged into another branch; use <a href="git-revert.html" target="_top">git-revert(1)</a> instead in |
| that case.</p><p>It is also possible to edit commits further back in the history, but |
| this is an advanced topic to be left for |
| <a href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">another chapter</a>.</p></div><div class="section" lang="en"><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 |
| useful to check out an older version of a particular file using |
| <a href="git-checkout.html" target="_top">git-checkout(1)</a>. We've used git checkout before to switch |
| branches, but it has quite different behavior if it is given a path |
| 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 |
| 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 |
| modifying the working directory, you can do that with |
| <a 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><div class="section" lang="en"><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 |
| information from taking up to much space on disk or in memory.</p><p>This compression is not performed automatically. Therefore you |
| should occasionally run <a 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 |
| you may prefer to run git-gc when you are not doing other work.</p></div><div class="section" lang="en"><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" lang="en"><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 href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks |
| on the repository, and reports on any problems. This may take some |
| time. The most common warning by far is about "dangling" objects:</p><div class="literallayout"><p>$ git fsck<br> |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br> |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br> |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br> |
| dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb<br> |
| dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f<br> |
| dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e<br> |
| dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085<br> |
| dangling tree b24c2473f1fd3d91352a624795be026d64c8841f<br> |
| ...</p></div><p>Dangling objects are not a problem. At worst they may take up a little |
| extra disk space. They can sometimes provide a last-resort method for |
| recovering lost work—see <a href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for details. However, if |
| you wish, you can remove them with <a href="git-prune.html" target="_top">git-prune(1)</a> or the —prune |
| option to <a href="git-gc.html" target="_top">git-gc(1)</a>:</p><div class="literallayout"><p>$ git gc --prune</p></div><p>This may be time-consuming. Unlike most other git operations (including |
| git-gc when run without any options), it is not safe to prune while |
| other git operations are in progress in the same repository.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-lost-changes"></a>Recovering lost changes</h3></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="reflogs"></a>Reflogs</h4></div></div></div><p>Say you modify a branch with <a href="git-reset.html" target="_top">git-reset(1)</a> —hard, and then |
| realize that the branch was the only reference you had to that point in |
| history.</p><p>Fortunately, git also keeps a log, called a "reflog", of all the |
| previous values of each branch. So in this case you can still find the |
| 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 head. |
| This syntax can be used to with any git command 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> |
| $ git show master@{3} # 3, ... changes ago.<br> |
| $ gitk master@{yesterday} # See where it pointed yesterday,<br> |
| $ gitk master@{"1 week ago"} # ... or last week<br> |
| $ 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 |
| pointed to one week ago. This allows you to see the history of what |
| you've checked out.</p><p>The reflogs are kept by default for 30 days, after which they may be |
| pruned. See <a href="git-reflog.html" target="_top">git-reflog(1)</a> and <a href="git-gc.html" target="_top">git-gc(1)</a> to learn |
| how to control this pruning, and see the "SPECIFYING REVISIONS" |
| section of <a 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. |
| While normal history is shared by every repository that works on the |
| same project, the reflog history is not shared: it tells you only about |
| how the branches in your local repository have changed over time.</p></div><div class="section" lang="en"><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, |
| suppose you delete a branch, then realize you need the history it |
| contained. The reflog is also deleted; however, if you have not yet |
| pruned the repository, then you may still be able to find the lost |
| commits in the dangling objects that git-fsck reports. See |
| <a href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for the details.</p><div class="literallayout"><p>$ git fsck<br> |
| dangling commit 7281251ddd2a61e38657c827739c57015671a6b3<br> |
| dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63<br> |
| dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5<br> |
| ...</p></div><p>You can examine |
| 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 |
| history that is described by the dangling commit(s), but not the |
| history that is described by all your existing branches and tags. Thus |
| you get exactly the history reachable from that commit that is lost. |
| (And notice that it might not be just one commit: we only report the |
| "tip of the line" as being dangling, but there might be a whole deep |
| and complex commit history that was dropped.)</p><p>If you decide you want the history back, you can always create a new |
| 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 |
| dangling objects can arise in other situations.</p></div></div></div></div><div class="chapter" lang="en"><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="#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" lang="en"><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 make a few changes of your own, you |
| may wish to check the original repository for updates and merge them |
| into your own work.</p><p>We have already seen <a 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 href="git-fetch.html" target="_top">git-fetch(1)</a>, |
| and how to merge two branches. So you can merge in changes from the |
| original repository's master branch with:</p><div class="literallayout"><p>$ git fetch<br> |
| $ git merge origin/master</p></div><p>However, the <a href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in |
| one step:</p><div class="literallayout"><p>$ git pull origin master</p></div><p>In fact, "origin" is normally the default repository to pull from, |
| and the default branch is normally the HEAD of the remote repository, |
| so often you can accomplish the above with just</p><div class="literallayout"><p>$ git pull</p></div><p>See the descriptions of the branch.<name>.remote and branch.<name>.merge |
| options in <a href="git-config.html" target="_top">git-config(1)</a> to learn how to control these defaults |
| depending on the current branch. Also note that the —track option to |
| <a href="git-branch.html" target="_top">git-branch(1)</a> and <a href="git-checkout.html" target="_top">git-checkout(1)</a> can be used to |
| automatically set the default remote branch to pull from at the time |
| that a branch is created:</p><div class="literallayout"><p>$ git checkout --track -b maint origin/maint</p></div><p>In addition to saving you keystrokes, "git pull" also helps you by |
| producing a default commit message documenting the branch and |
| repository that you pulled from.</p><p>(But note that no such commit will be created in the case of a |
| <a href="#fast-forwards" title="Fast-forward merges">fast forward</a>; instead, your branch will just be |
| updated to point to the latest commit from the upstream branch.)</p><p>The git-pull command can also be given "." as the "remote" repository, |
| in which case it just merges in a branch from the current repository; so |
| the commands</p><div class="literallayout"><p>$ git pull . branch<br> |
| $ git merge branch</p></div><p>are roughly equivalent. The former is actually very commonly used.</p></div><div class="section" lang="en"><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 |
| just be to send them as patches in email:</p><p>First, use <a 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 |
| 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 |
| hand. However, if you have a lot to send at once, you may prefer to |
| use the <a href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process. |
| Consult the mailing list for your project first to determine how they |
| prefer such patches be handled.</p></div><div class="section" lang="en"><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 href="git-am.html" target="_top">git-am(1)</a> (am stands for |
| "apply mailbox"), for importing such an emailed series of patches. |
| Just save all of the patch-containing messages, in order, into a |
| 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 |
| will stop, and you can fix the conflicts as described in |
| "<a href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The "-3" option tells |
| git to perform a merge; if you would prefer it just to abort and |
| leave your tree and index untouched, you may omit that option.)</p><p>Once the index is updated with the results of the conflict |
| 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 |
| remaining patches from the mailbox.</p><p>The final result will be a series of commits, one for each patch in |
| the original mailbox, with authorship and commit log message each |
| taken from the message containing each patch.</p></div><div class="section" lang="en"><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 of |
| that project to pull the changes from your repository using git-pull[1]. |
| In the section "<a href="#getting-updates-with-git-pull" title="Getting updates with git pull">Getting updates with git pull</a>" we described this as a way to get updates from the "main" |
| repository, but it works just as well in the other direction.</p><p>If you and the maintainer both have accounts on the same machine, then |
| you can just pull changes from each other's repositories directly; |
| commands that accept repository URLs as arguments will also accept a |
| local directory name:</p><div class="literallayout"><p>$ git clone /path/to/repository<br> |
| $ 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 |
| repositories, this may be all you need.</p><p>However, the more common way to do this is to maintain a separate public |
| repository (usually on a different host) for others to pull changes |
| from. This is usually more convenient, and allows you to cleanly |
| separate private work in progress from publicly visible work.</p><p>You will continue to do your day-to-day work in your personal |
| repository, but periodically "push" changes from your personal |
| repository into your public repository, allowing other developers to |
| pull from that repository. So the flow of changes, in a situation |
| where there is one other developer with a public repository, looks |
| like this:</p><pre class="literallayout"> you push |
| your personal repo ------------------> your public repo |
| ^ | |
| | | |
| | you pull | they pull |
| | | |
| | | |
| | they push V |
| their public repo <------------------- their repo</pre><p>We explain how to do this in the following sections.</p><div class="section" lang="en"><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 |
| first create a new clone of the repository and tell git-daemon that it |
| is meant to be public:</p><div class="literallayout"><p>$ git clone --bare ~/proj proj.git<br> |
| $ touch proj.git/git-daemon-export-ok</p></div><p>The resulting directory proj.git contains a "bare" git repository—it is |
| just the contents of the ".git" directory, without any files checked out |
| around it.</p><p>Next, copy proj.git to the server where you plan to host the |
| public repository. You can use scp, rsync, or whatever is most |
| convenient.</p></div><div class="section" lang="en"><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 |
| directory to put the repository in, and what git:// url it will appear |
| at. You can then skip to the section |
| "<a 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 href="git-daemon.html" target="_top">git-daemon(1)</a>; it will |
| listen on port 9418. By default, it will allow access to any directory |
| that looks like a git directory and contains the magic file |
| git-daemon-export-ok. Passing some directory paths as git-daemon |
| arguments will further restrict the exports to those paths.</p><p>You can also run git-daemon as an inetd service; see the |
| <a href="git-daemon.html" target="_top">git-daemon(1)</a> man page for details. (See especially the |
| examples section.)</p></div><div class="section" lang="en"><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 |
| 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 |
| a directory that is exported by the web server, and make some |
| 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> |
| $ cd proj.git<br> |
| $ git --bare update-server-info<br> |
| $ chmod a+x hooks/post-update</p></div><p>(For an explanation of the last two lines, see |
| <a href="git-update-server-info.html" target="_top">git-update-server-info(1)</a>, and the documentation |
| <a href="hooks.html" target="_top">Hooks used by git</a>.)</p><p>Advertise the url of proj.git. Anybody else should then be able to |
| clone or pull from that url, for example with a commandline like:</p><div class="literallayout"><p>$ git clone http://yourserver.com/~you/proj.git</p></div><p>(See also |
| <a href="howto/setup-git-server-over-http.txt" target="_top">setup-git-server-over-http</a> |
| for a slightly more sophisticated setup using WebDAV which also |
| allows pushing over http.)</p></div><div class="section" lang="en"><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 |
| <a href="#exporting-via-http" title="Exporting a git repository via http">http</a> or <a href="#exporting-via-git" title="Exporting a git repository via the git protocol">git</a>) allow other |
| maintainers to fetch your latest changes, but they do not allow write |
| access, which you will need to update the public repository with the |
| latest changes created in your private repository.</p><p>The simplest way to do this is using <a href="git-push.html" target="_top">git-push(1)</a> and ssh; to |
| update the remote branch named "master" with the latest state of your |
| 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 git-fetch, git-push will complain if this does not result in |
| a <a href="#fast-forwards" title="Fast-forward merges">fast forward</a>. Normally this is a sign of |
| something wrong. However, if you are sure you know what you're |
| doing, you may force git-push to perform the update anyway by |
| proceeding the branch name by a plus sign:</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git +master</p></div><p>Note that the target of a "push" is normally a |
| <a href="#def_bare_repository">bare</a> repository. You can also push to a |
| repository that has a checked-out working tree, but the working tree |
| will not be updated by the push. This may lead to unexpected results if |
| the branch you push to is the currently checked-out branch!</p><p>As with git-fetch, you may also set up configuration options to |
| save typing; so, for example, after</p><div class="literallayout"><p>$ cat >>.git/config <<EOF<br> |
| [remote "public-repo"]<br> |
| url = ssh://yourserver.com/~you/proj.git<br> |
| 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, |
| and remote.<name>.push options in <a href="git-config.html" target="_top">git-config(1)</a> for |
| details.</p></div><div class="section" lang="en"><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 |
| commonly used in CVS, where several developers with special rights |
| all push to and pull from a single shared repository. See |
| <a href="cvs-migration.html" target="_top">git for CVS users</a> for instructions on how to |
| set this up.</p><p>However, while there is nothing wrong with git's support for shared |
| repositories, this mode of operation is not generally recommended, |
| simply because the mode of collaboration that git supports—by |
| exchanging patches and pulling from public repositories—has so many |
| advantages over the central shared repository:</p><div class="itemizedlist"><ul type="disc"><li> |
| Git's ability to quickly import and merge patches allows a |
| single maintainer to process incoming changes even at very |
| high rates. And when that becomes too much, git-pull provides |
| an easy way for that maintainer to delegate this job to other |
| maintainers while still allowing optional review of incoming |
| changes. |
| </li><li> |
| Since every developer's repository has the same complete copy |
| of the project history, no repository is special, and it is |
| trivial for another developer to take over maintenance of a |
| project, either by mutual agreement, or because a maintainer |
| becomes unresponsive or difficult to work with. |
| </li><li> |
| The lack of a central group of "committers" means there is |
| less need for formal decisions about who is "in" and who is |
| "out". |
| </li></ul></div></div><div class="section" lang="en"><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 |
| project's files and history without having to install git; see the file |
| gitweb/INSTALL in the git source tree for instructions on setting it up.</p></div></div><div class="section" lang="en"><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" lang="en"><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 |
| IA64 architecture for the Linux kernel.</p><p>He uses two public branches:</p><div class="itemizedlist"><ul type="disc"><li> |
| A "test" tree into which patches are initially placed so that they |
| can get some exposure when integrated with other ongoing development. |
| This tree is available to Andrew for pulling into -mm whenever he |
| wants. |
| </li><li> |
| A "release" tree into which tested patches are moved for final sanity |
| checking, and as a vehicle to send them upstream to Linus (by sending |
| him a "please pull" request.) |
| </li></ul></div><p>He also uses a set of temporary branches ("topic branches"), each |
| containing a logical grouping of patches.</p><p>To set this up, first create your work tree by cloning Linus's public |
| tree:</p><div class="literallayout"><p>$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work<br> |
| $ cd work</p></div><p>Linus's tree will be stored in the remote branch named origin/master, |
| and can be updated using <a href="git-fetch.html" target="_top">git-fetch(1)</a>; you can track other |
| public trees using <a href="git-remote.html" target="_top">git-remote(1)</a> to set up a "remote" and |
| git-fetch[1] to keep them up-to-date; see <a 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 |
| at the current tip of origin/master branch, and should be set up (using |
| the —track option to <a href="git-branch.html" target="_top">git-branch(1)</a>) to merge changes in from |
| Linus by default.</p><div class="literallayout"><p>$ git branch --track test origin/master<br> |
| $ git branch --track release origin/master</p></div><p>These can be easily kept up to date using <a href="git-pull.html" target="_top">git-pull(1)</a></p><div class="literallayout"><p>$ git checkout test && git pull<br> |
| $ git checkout release && git pull</p></div><p>Important note! If you have any local changes in these branches, then |
| this merge will create a commit object in the history (with no local |
| changes git will simply do a "Fast forward" merge). Many people dislike |
| the "noise" that this creates in the Linux history, so you should avoid |
| doing this capriciously in the "release" branch, as these noisy commits |
| will become part of the permanent history when you ask Linus to pull |
| from the release branch.</p><p>A few configuration variables (see <a href="git-config.html" target="_top">git-config(1)</a>) can |
| make it easy to push both branches to your public tree. (See |
| <a 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> |
| [remote "mytree"]<br> |
| url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git<br> |
| push = release<br> |
| push = test<br> |
| EOF</p></div><p>Then you can push both the test and release trees using |
| <a 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 |
| snappy name for a branch to hold this patch (or related group of |
| patches), and create a new branch from the current tip of Linus's |
| 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 |
| the patch is a multi-part series, then you should apply each as a separate |
| 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 |
| "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 |
| 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 |
| same branch into the "release" tree ready to go upstream. This is where you |
| see the value of keeping each patch (or patch series) in its own branch. It |
| 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 |
| well chosen names you picked for each of them, you may forget what |
| they are for, or what status they are in. To get a reminder of what |
| 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 |
| 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. |
| 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, |
| then pulled by Linus, and finally coming back into your local |
| "origin/master" branch) the branch for this change is no longer needed. |
| 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 |
| branch and then merge into each of the test and release branches. For |
| these changes, just apply directly to the "release" branch, and then |
| merge that into the "test" branch.</p><p>To create diffstat and shortlog summaries of changes to include in a "please |
| 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> |
| # Update a branch in my GIT tree. If the branch to be updated<br> |
| # is origin, then pull from kernel.org. Otherwise merge<br> |
| # origin/master branch into test|release branch<br> |
| <br> |
| case "$1" in<br> |
| test|release)<br> |
| git checkout $1 && git pull . origin<br> |
| ;;<br> |
| origin)<br> |
| before=$(cat .git/refs/remotes/origin/master)<br> |
| git fetch origin<br> |
| after=$(cat .git/refs/remotes/origin/master)<br> |
| if [ $before != $after ]<br> |
| then<br> |
| git log $before..$after | git shortlog<br> |
| fi<br> |
| ;;<br> |
| *)<br> |
| echo "Usage: $0 origin|test|release" 1>&2<br> |
| exit 1<br> |
| ;;<br> |
| esac</p></div><div class="literallayout"><p>==== merge script ====<br> |
| # Merge a branch into either the test or release branch<br> |
| <br> |
| pname=$0<br> |
| <br> |
| usage()<br> |
| {<br> |
| echo "Usage: $pname branch test|release" 1>&2<br> |
| exit 1<br> |
| }<br> |
| <br> |
| if [ ! -f .git/refs/heads/"$1" ]<br> |
| then<br> |
| echo "Can't see branch <$1>" 1>&2<br> |
| usage<br> |
| fi<br> |
| <br> |
| case "$2" in<br> |
| test|release)<br> |
| if [ $(git log $2..$1 | wc -c) -eq 0 ]<br> |
| then<br> |
| echo $1 already merged into $2 1>&2<br> |
| exit 1<br> |
| fi<br> |
| git checkout $2 && git pull . $1<br> |
| ;;<br> |
| *)<br> |
| usage<br> |
| ;;<br> |
| esac</p></div><div class="literallayout"><p>==== status script ====<br> |
| # report on status of my ia64 GIT tree<br> |
| <br> |
| gb=$(tput setab 2)<br> |
| rb=$(tput setab 1)<br> |
| restore=$(tput setab 9)<br> |
| <br> |
| if [ `git rev-list test..release | wc -c` -gt 0 ]<br> |
| then<br> |
| echo $rb Warning: commits in release that are not in test $restore<br> |
| git log test..release<br> |
| fi<br> |
| <br> |
| for branch in `ls .git/refs/heads`<br> |
| do<br> |
| if [ $branch = test -o $branch = release ]<br> |
| then<br> |
| continue<br> |
| fi<br> |
| <br> |
| echo -n $gb ======= $branch ====== $restore " "<br> |
| status=<br> |
| for ref in test release origin/master<br> |
| do<br> |
| if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]<br> |
| then<br> |
| status=$status${ref:0:1}<br> |
| fi<br> |
| done<br> |
| case $status in<br> |
| trl)<br> |
| echo $rb Need to pull into test $restore<br> |
| ;;<br> |
| rl)<br> |
| echo "In test"<br> |
| ;;<br> |
| l)<br> |
| echo "Waiting for linus"<br> |
| ;;<br> |
| "")<br> |
| echo $rb All done $restore<br> |
| ;;<br> |
| *)<br> |
| echo $rb "<$status>" $restore<br> |
| ;;<br> |
| esac<br> |
| git log origin/master..$branch | git shortlog<br> |
| done</p></div></div></div></div><div class="chapter" lang="en"><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="#modifying-one-commit">Modifying 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></dl></div><p>Normally commits are only added to a project, never taken away or |
| replaced. Git is designed with this assumption, and violating it will |
| 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 |
| assumption.</p><div class="section" lang="en"><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 |
| complicated feature, and to present it to the other developers in a way |
| that makes it easy for them to read your changes, verify that they are |
| correct, and understand why you made each change.</p><p>If you present all of your changes as a single patch (or commit), they |
| 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 |
| 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 type="1"><li> |
| Each patch can be applied in order. |
| </li><li> |
| Each patch includes a single logical change, together with a |
| message explaining the change. |
| </li><li> |
| No patch introduces a regression: after applying any initial |
| part of the series, the resulting project still compiles and |
| works, and has no bugs that it didn't have before. |
| </li><li> |
| The complete series produces the same end result as your own |
| (probably much messier!) development process did. |
| </li></ol></div><p>We will introduce some tools that can help you do this, explain how to |
| use them, and then explain some of the problems that can arise because |
| you are rewriting history.</p></div><div class="section" lang="en"><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 |
| "origin", and create some commits on top of it:</p><div class="literallayout"><p>$ git checkout -b mywork origin<br> |
| $ vi file.txt<br> |
| $ git commit<br> |
| $ vi otherfile.txt<br> |
| $ git commit<br> |
| ...</p></div><p>You have performed no merges into mywork, so it is just a simple linear |
| sequence of patches on top of "origin":</p><pre class="literallayout"> o--o--o <-- origin |
| \ |
| o--o--o <-- mywork</pre><p>Some more interesting work has been done in the upstream project, and |
| "origin" has advanced:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ |
| a--b--c <-- mywork</pre><p>At this point, you could use "pull" to merge your changes back in; |
| the result would create a new merge commit, like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ \ |
| a--b--c--m <-- mywork</pre><p>However, if you prefer to keep the history in mywork a simple series of |
| commits without any merges, you may instead choose to use |
| <a href="git-rebase.html" target="_top">git-rebase(1)</a>:</p><div class="literallayout"><p>$ git checkout mywork<br> |
| $ git rebase origin</p></div><p>This will remove each of your commits from mywork, temporarily saving |
| them as patches (in a directory named ".dotest"), update mywork to |
| point at the latest version of origin, then apply each of the saved |
| patches to the new mywork. The result will look like:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ |
| a'--b'--c' <-- mywork</pre><p>In the process, it may discover conflicts. In that case it will stop |
| and allow you to fix the conflicts; after fixing conflicts, use "git |
| add" to update the index with those contents, and then, instead of |
| running git-commit, 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 —abort option to abort this process and |
| 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" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="modifying-one-commit"></a>Modifying a single commit</h2></div></div></div><p>We saw in <a href="#fixing-a-mistake-by-editing-history" title="Fixing a mistake by editing history">the section called “Fixing a mistake by editing history”</a> that you can replace the |
| 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 |
| changes, giving you a chance to edit the old commit message first.</p><p>You can also use a combination of this and <a href="git-rebase.html" target="_top">git-rebase(1)</a> to edit |
| commits further back in your history. First, tag the problematic commit with</p><div class="literallayout"><p>$ git tag bad mywork~5</p></div><p>(Either gitk or git-log may be useful for finding the commit.)</p><p>Then check out that commit, edit it, and rebase the rest of the series |
| on top of it (note that we could check out the commit on a temporary |
| branch, but instead we're using a <a 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> |
| $ # make changes here and update the index<br> |
| $ git commit --amend<br> |
| $ git rebase --onto HEAD bad mywork</p></div><p>When you're done, you'll be left with mywork checked out, with the top |
| patches on mywork reapplied on top of your modified commit. You can |
| 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 |
| "modified" existing commits; instead, you have replaced the old commits with |
| new commits having new object names.</p></div><div class="section" lang="en"><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 href="git-cherry-pick.html" target="_top">git-cherry-pick(1)</a> command |
| allows you to apply the change introduced by that commit and create a |
| new commit that records it. So, for example, if "mywork" points to a |
| series of patches on top of "origin", you might do something like:</p><div class="literallayout"><p>$ git checkout -b mywork-new origin<br> |
| $ gitk origin..mywork &</p></div><p>And browse through the list of patches in the mywork branch using gitk, |
| applying them (possibly in a different order) to mywork-new using |
| cherry-pick, and possibly modifying them as you go using commit |
| —amend.</p><p>Another technique is to use git-format-patch to create a series of |
| patches, then reset the state to before the patches:</p><div class="literallayout"><p>$ git format-patch origin<br> |
| $ git reset --hard origin</p></div><p>Then modify, reorder, or eliminate patches as preferred before applying |
| them again with <a href="git-am.html" target="_top">git-am(1)</a>.</p></div><div class="section" lang="en"><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 |
| purpose of maintaining a patch series. These are outside of the scope of |
| this manual.</p></div><div class="section" lang="en"><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 |
| with merging. Suppose somebody fetches your branch and merges it into |
| their branch, with a result something like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin |
| \ \ |
| 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 |
| / |
| o--o--O--o--o--o <-- old head of origin</pre><p>If we examined all this history together in one repository, it will |
| look like:</p><pre class="literallayout"> o--o--o <-- new head of origin |
| / |
| o--o--O--o--o--o <-- old head of origin |
| \ \ |
| t--t--t--m <-- their branch:</pre><p>Git has no way of knowing that the new head is an updated version of |
| the old head; it treats this situation exactly the same as it would if |
| two developers had independently done the work on the old and new heads |
| in parallel. At this point, if someone attempts to merge the new head |
| in to their branch, git will attempt to merge together the two (old and |
| new) lines of development, instead of trying to replace the old by the |
| new. The results are likely to be unexpected.</p><p>You may still choose to publish branches whose history is rewritten, |
| and it may be useful for others to be able to fetch those branches in |
| order to examine or test them, but they should not attempt to pull such |
| branches into their own work.</p><p>For true distributed development that supports proper merging, |
| published branches should never be rewritten.</p></div></div><div class="chapter" lang="en"><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" lang="en"><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 href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just |
| to update one branch at a time, and to store it locally under an |
| 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 |
| repository you originally cloned from. The second argument tells git |
| to fetch the branch named "todo" from the remote repository, and to |
| 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 |
| branch named "master" from the repository at the given URL. If you |
| already have a branch named example-master, it will attempt to |
| <a href="#fast-forwards" title="Fast-forward merges">fast-forward</a> to the commit given by example.com's |
| master branch. In more detail:</p></div><div class="section" lang="en"><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" checks to make sure that the most recent commit on the remote |
| branch is a descendant of the most recent commit on your copy of the |
| branch before updating your copy of the branch to point at the new |
| commit. Git calls this process a <a 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 |
| \ |
| 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 |
| a descendant of the old head. For example, the developer may have |
| realized she made a serious mistake, and decided to backtrack, |
| resulting in a situation like:</p><pre class="literallayout"> o--o--o--o--a--b <-- old head of the branch |
| \ |
| 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 |
| described in the following section. However, note that in the |
| situation above this may mean losing the commits labeled "a" and "b", |
| unless you've already created a reference of your own pointing to |
| them.</p></div><div class="section" lang="en"><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 |
| 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" |
| 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 |
| may be lost, as we saw in the previous section.</p></div><div class="section" lang="en"><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 |
| repository that you originally cloned from. This information is |
| stored in git configuration variables, which you can see using |
| <a href="git-config.html" target="_top">git-config(1)</a>:</p><div class="literallayout"><p>$ git config -l<br> |
| core.repositoryformatversion=0<br> |
| core.filemode=true<br> |
| core.logallrefupdates=true<br> |
| remote.origin.url=git://git.kernel.org/pub/scm/git/git.git<br> |
| remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*<br> |
| branch.master.remote=origin<br> |
| branch.master.merge=refs/heads/master</p></div><p>If there are other repositories that you also use frequently, you can |
| create similar configuration options to save typing; for example, |
| 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> |
| $ 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> |
| $ git fetch example master:refs/remotes/example/master<br> |
| $ 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 |
| throwing away commits on mybranch.</p><p>Also note that all of the above configuration can be performed by |
| directly editing the file .git/config instead of using |
| <a href="git-config.html" target="_top">git-config(1)</a>.</p><p>See <a href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration |
| options mentioned above.</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="git-internals"></a>Chapter 7. Git internals</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><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#commit-object">Commit 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="#the-index">The "index" aka "Current Directory Cache"</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><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="#birdview-on-the-source-code">A birds-eye view of Git's source code</a></span></dt></dl></div><p>Git depends on two fundamental abstractions: the "object database", and |
| the "current directory cache" aka "index".</p><div class="section" lang="en"><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>The object database is literally just a content-addressable collection |
| of objects. All objects are named by their content, which is |
| approximated by the SHA1 hash of the object itself. Objects may refer |
| to other objects (by referencing their SHA1 hash), and so you can |
| build up a hierarchy of objects.</p><p>All objects have a statically determined "type" which is |
| determined at object creation time, and which identifies the format of |
| the object (i.e. how it is used, and how it can refer to other |
| objects). There are currently four different object types: "blob", |
| "tree", "commit", and "tag".</p><p>A <a href="#def_blob_object">"blob" object</a> cannot refer to any other object, |
| and is, as the name implies, a pure storage object containing some |
| user data. It is used to actually store the file data, i.e. a blob |
| object is associated with some particular version of some file.</p><p>A <a href="#def_tree_object">"tree" object</a> is an object that ties one or more |
| "blob" objects into a directory structure. In addition, a tree object |
| can refer to other tree objects, thus creating a directory hierarchy.</p><p>A <a href="#def_commit_object">"commit" object</a> ties such directory hierarchies |
| together into a <a href="#def_DAG">directed acyclic graph</a> of revisions - each |
| "commit" is associated with exactly one tree (the directory hierarchy at |
| the time of the commit). In addition, a "commit" refers to one or more |
| "parent" commit objects that describe the history of how we arrived at |
| that directory hierarchy.</p><p>As a special case, a commit object with no parents is called the "root" |
| commit, and is the point of an initial project commit. Each project |
| must have at least one root, and while you can tie several different |
| root objects together into one project by creating a commit object which |
| has two or more separate roots as its ultimate parents, that's probably |
| just going to confuse people. So aim for the notion of "one root object |
| per project", even if git itself does not enforce that.</p><p>A <a href="#def_tag_object">"tag" object</a> symbolically identifies and can be |
| used to sign other objects. It contains the identifier and type of |
| another object, a symbolic name (of course!) and, optionally, a |
| signature.</p><p>Regardless of object type, all objects share the following |
| characteristics: they are all deflated with zlib, and have a header |
| that not only specifies their type, but also provides size information |
| about the data in the object. It's worth noting that the SHA1 hash |
| that is used to name the object is the hash of the original data |
| plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name |
| for <span class="emphasis"><em>file</em></span>. |
| (Historical note: in the dawn of the age of git the hash |
| was the sha1 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 |
| independently of the contents or the type of the object: all objects can |
| be validated by verifying that (a) their hashes match the content of the |
| file and (b) the object successfully inflates to a stream of bytes that |
| forms a sequence of <ascii type without space> + <space> + <ascii decimal |
| size> + <byte\0> + <binary object data>.</p><p>The structured objects can further have their structure and |
| connectivity to other objects verified. This is generally done with |
| the <code class="literal">git-fsck</code> program, which generates a full dependency graph |
| of all objects, and verifies their internal consistency (in addition |
| to just verifying their superficial consistency through the hash).</p><p>The object types in some more detail:</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="blob-object"></a>Blob Object</h2></div></div></div><p>A "blob" object is nothing but a binary blob of data, and doesn't |
| refer to anything else. There is no signature or any other |
| verification of the data, so while the object is consistent (it <span class="emphasis"><em>is</em></span> |
| indexed by its sha1 hash, so the data itself is certainly correct), it |
| has absolutely no other attributes. No name associations, no |
| permissions. It is purely a blob of data (i.e. normally "file |
| contents").</p><p>In particular, since the blob is entirely defined by its data, if two |
| files in a directory tree (or in multiple different versions of the |
| repository) have the same contents, they will share the same blob |
| object. The object is totally independent of its location in the |
| directory tree, and renaming a file does not change the object that |
| file is associated with in any way.</p><p>A blob is typically created when <a href="git-update-index.html" target="_top">git-update-index(1)</a> |
| is run, and its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="tree-object"></a>Tree Object</h2></div></div></div><p>The next hierarchical object type is the "tree" object. A tree object |
| is a list of mode/name/blob data, sorted by name. Alternatively, the |
| mode data may specify a directory mode, in which case instead of |
| naming a blob, that name is associated with another TREE object.</p><p>Like the "blob" object, a tree object is uniquely determined by the |
| set contents, and so two separate but identical trees will always |
| share the exact same object. This is true at all levels, i.e. it's |
| true for a "leaf" tree (which does not refer to any other trees, only |
| blobs) as well as for a whole subdirectory.</p><p>For that reason a "tree" object is just a pure data abstraction: it |
| has no history, no signatures, no verification of validity, except |
| that since the contents are again protected by the hash itself, we can |
| trust that the tree is immutable and its contents never change.</p><p>So you can trust the contents of a tree to be valid, the same way you |
| can trust the contents of a blob, but you don't know where those |
| contents <span class="emphasis"><em>came</em></span> from.</p><p>Side note on trees: since a "tree" object is a sorted list of |
| "filename+content", you can create a diff between two trees without |
| actually having to unpack two trees. Just ignore all common parts, |
| and your diff will look right. In other words, you can effectively |
| (and efficiently) tell the difference between any two random trees by |
| O(n) where "n" is the size of the difference, rather than the size of |
| the tree.</p><p>Side note 2 on trees: since the name of a "blob" depends entirely and |
| exclusively on its contents (i.e. there are no names or permissions |
| involved), you can see trivial renames or permission changes by |
| noticing that the blob stayed the same. However, renames with data |
| changes need a smarter "diff" implementation.</p><p>A tree is created with <a href="git-write-tree.html" target="_top">git-write-tree(1)</a> and |
| its data can be accessed by <a href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. |
| Two trees can be compared with <a href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="commit-object"></a>Commit Object</h2></div></div></div><p>The "commit" object is an object that introduces the notion of |
| history into the picture. In contrast to the other objects, it |
| doesn't just describe the physical state of a tree, it describes how |
| we got there, and why.</p><p>A "commit" is defined by the tree-object that it results in, the |
| parent commits (zero, one or more) that led up to that point, and a |
| comment on what happened. Again, a commit is not trusted per se: |
| the contents are well-defined and "safe" due to the cryptographically |
| strong signatures at all levels, but there is no reason to believe |
| that the tree is "good" or that the merge information makes sense. |
| The parents do not have to actually have any relationship with the |
| result, for example.</p><p>Note on commits: unlike some SCM's, commits do not contain |
| rename information or file mode change information. All of that is |
| implicit in the trees involved (the result tree, and the result trees |
| of the parents), and describing that makes no sense in this idiotic |
| file manager.</p><p>A commit is created with <a href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> and |
| its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="trust"></a>Trust</h2></div></div></div><p>An aside on the notion of "trust". Trust is really outside the scope |
| of "git", but it's worth noting a few things. First off, since |
| everything is hashed with SHA1, you <span class="emphasis"><em>can</em></span> trust that an object is |
| intact and has not been messed with by external sources. So the name |
| of an object uniquely identifies a known state - just not a state that |
| you may want to trust.</p><p>Furthermore, since the SHA1 signature of a commit refers to the |
| SHA1 signatures of the tree it is associated with and the signatures |
| of the parent, a single named commit specifies uniquely a whole set |
| of history, with full contents. You can't later fake any step of the |
| way once you have the name of a commit.</p><p>So to introduce some real trust in the system, the only thing you need |
| to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the |
| name of a top-level commit. Your digital signature shows others |
| that you trust that commit, and the immutability of the history of |
| commits tells others that they can trust the whole history.</p><p>In other words, you can easily validate a whole archive by just |
| sending out a single email that tells the people the name (SHA1 hash) |
| of the top commit, and digitally sign that email using something |
| like GPG/PGP.</p><p>To assist in this, git also provides the tag object…</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="tag-object"></a>Tag Object</h2></div></div></div><p>Git provides the "tag" object to simplify creating, managing and |
| exchanging symbolic and signed tokens. The "tag" object at its |
| simplest simply symbolically identifies another object by containing |
| the sha1, type and symbolic name.</p><p>However it can optionally contain additional signature information |
| (which git doesn't care about as long as there's less than 8k of |
| it). This can then be verified externally to git.</p><p>Note that despite the tag features, "git" itself only handles content |
| integrity; the trust framework (and signature provision and |
| verification) has to come from outside.</p><p>A tag is created with <a href="git-mktag.html" target="_top">git-mktag(1)</a>, |
| its data can be accessed by <a href="git-cat-file.html" target="_top">git-cat-file(1)</a>, |
| and the signature can be verified by |
| <a href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-index"></a>The "index" aka "Current Directory Cache"</h2></div></div></div><p>The index is a simple binary file, which contains an efficient |
| representation of the contents of a virtual directory. It |
| does so by a simple array that associates a set of names, dates, |
| permissions and content (aka "blob") objects together. The cache is |
| always kept ordered by name, and names are unique (with a few very |
| specific rules) at any point in time, but the cache has no long-term |
| meaning, and can be partially updated at any time.</p><p>In particular, the index certainly does not need to be consistent with |
| the current directory contents (in fact, most operations will depend on |
| different ways to make the index <span class="emphasis"><em>not</em></span> be consistent with the directory |
| hierarchy), but it has three very important attributes:</p><p><span class="emphasis"><em>(a) it can re-generate the full state it caches (not just the |
| directory structure: it contains pointers to the "blob" objects so |
| that it can regenerate the data too)</em></span></p><p>As a special case, there is a clear and unambiguous one-way mapping |
| from a current directory cache to a "tree object", which can be |
| efficiently created from just the current directory cache without |
| actually looking at any other data. So a directory cache at any one |
| time uniquely specifies one and only one "tree" object (but has |
| additional data to make it easy to match up that tree object with what |
| has happened in the directory)</p><p><span class="emphasis"><em>(b) it has efficient methods for finding inconsistencies between that |
| cached state ("tree object waiting to be instantiated") and the |
| current state.</em></span></p><p><span class="emphasis"><em>(c) it can additionally efficiently represent information about merge |
| conflicts between different tree objects, allowing each pathname to be |
| associated with sufficient information about the trees involved that |
| you can create a three-way merge between them.</em></span></p><p>Those are the ONLY three things that the directory cache does. It's a |
| cache, and the normal operation is to re-generate it completely from a |
| known tree object, or update/compare it with a live tree that is being |
| developed. If you blow the directory cache away entirely, you generally |
| haven't lost any information as long as you have the name of the tree |
| that it described.</p><p>At the same time, the index is also the staging area for creating |
| new trees, and creating a new tree always involves a controlled |
| modification of the index file. In particular, the index file can |
| have the representation of an intermediate tree that has not yet been |
| instantiated. So the index can be thought of as a write-back cache, |
| which can contain dirty information that has not yet been written back |
| to the backing store.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-workflow"></a>The Workflow</h2></div></div></div><p>Generally, all "git" operations work on the index file. Some operations |
| work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the |
| index), but most operations move data to and from the index file. Either |
| from the database or from the working directory. Thus there are four |
| main combinations:</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="working-directory-to-index"></a>working directory -> index</h3></div></div></div><p>You update the index with information from the working directory with |
| the <a href="git-update-index.html" target="_top">git-update-index(1)</a> command. You |
| generally update the index information by just specifying the filename |
| you want to update, 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 |
| will not normally add totally new entries or remove old entries, |
| 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 |
| longer exist, or that new files should be added, you |
| 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 |
| necessarily be removed: if the files still exist in your directory |
| structure, the index will be updated with their new status, not |
| removed. The only thing <code class="literal">—remove</code> means is that update-cache will be |
| considering a removed file to be a valid thing, and if the file really |
| 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 |
| will refresh the "stat" information of each index to match the current |
| stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and |
| it will only update the fields that are used to quickly test whether |
| an object still matches its old backing store object.</p></div><div class="section" lang="en"><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 |
| current index into the set of tree objects that describe that state, |
| and it will return the name of the resulting top-level tree. You can |
| use that tree to re-generate the index at any time by going in the |
| other direction:</p></div><div class="section" lang="en"><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 |
| populate (and overwrite - don't do this if your index contains any |
| unsaved state that you might want to restore later!) your current |
| index. Normal operation is just</p><div class="literallayout"><p>$ git-read-tree <sha1 of tree></p></div><p>and your index file will now be equivalent to the tree that you saved |
| earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working |
| directory contents have not been modified.</p></div><div class="section" lang="en"><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" |
| files. This is not a very common operation, since normally you'd just |
| keep your files updated, and rather than write to your working |
| directory, you'd tell the index files about the changes in your |
| 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 |
| else's version, or just restore a previous tree, you'd populate your |
| index file with read-tree, and then you need to check out the result |
| 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! git-checkout-index normally refuses to overwrite old files, so |
| if you have an old version of the tree already checked out, you will |
| need to use the "-f" flag (<span class="emphasis"><em>before</em></span> the "-a" flag or the filename) to |
| <span class="emphasis"><em>force</em></span> the checkout.</p><p>Finally, there are a few odds and ends which are not purely moving |
| from one representation to the other:</p></div><div class="section" lang="en"><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 |
| create a "commit" object that refers to that tree and the history |
| behind it - most notably the "parent" commits that preceded it in |
| history.</p><p>Normally a "commit" has one parent: the previous state of the tree |
| before a certain change was made. However, sometimes it can have two |
| or more parent commits, in which case we call it a "merge", due to the |
| fact that such a commit brings together ("merges") two or more |
| previous states represented by other commits.</p><p>In other words, while a "tree" represents a particular directory state |
| of a working directory, a "commit" represents that state in "time", |
| and explains how we got there.</p><p>You create a commit object by giving it the tree that describes the |
| 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 |
| redirection from a pipe or file, or by just typing it at the tty).</p><p>git-commit-tree will return the name of the object that represents |
| that commit, and you should save it away for later use. Normally, |
| you'd commit a new <code class="literal">HEAD</code> state, and while git doesn't care where you |
| save the note about that state, in practice we tend to just write the |
| result to the file pointed at by <code class="literal">.git/HEAD</code>, so that we can always see |
| what the last committed state was.</p><p>Here is an ASCII art by Jon Loeliger that illustrates how |
| various pieces fit together.</p><div class="literallayout"><p><br> |
| commit-tree<br> |
| commit obj<br> |
| +----+<br> |
| | |<br> |
| | |<br> |
| V V<br> |
| +-----------+<br> |
| | Object DB |<br> |
| | Backing |<br> |
| | Store |<br> |
| +-----------+<br> |
| ^<br> |
| write-tree | |<br> |
| tree obj | |<br> |
| | | read-tree<br> |
| | | tree obj<br> |
| V<br> |
| +-----------+<br> |
| | Index |<br> |
| | "cache" |<br> |
| +-----------+<br> |
| update-index ^<br> |
| blob obj | |<br> |
| | |<br> |
| checkout-index -u | | checkout-index<br> |
| stat | | blob obj<br> |
| V<br> |
| +-----------+<br> |
| | Working |<br> |
| | Directory |<br> |
| +-----------+<br> |
| </p></div></div></div><div class="section" lang="en"><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 |
| index with various helper tools. For every object, you can use |
| <a href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the |
| 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 |
| 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 |
| there is a special helper for showing that content, called |
| <code class="literal">git-ls-tree</code>, which turns the binary content into a more easily |
| readable form.</p><p>It's especially instructive to look at "commit" objects, since those |
| tend to be small and fairly self-explanatory. In particular, if you |
| follow the convention of having the top commit name in <code class="literal">.git/HEAD</code>, |
| 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" lang="en"><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 |
| repeating the merge procedure arbitrary times until you finally |
| "commit" the state. The normal situation is that you'd only do one |
| three-way merge (two parents), and commit it, but if you like to, you |
| can do multiple parents in one go.</p><p>To do a three-way merge, you need the two sets of "commit" objects |
| that you want to merge, use those to find the closest common parent (a |
| third "commit" object), and then use those commit objects to find the |
| 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 |
| 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 |
| now look up the "tree" objects of those commits, which you can easily |
| 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 |
| object.</p><p>Once you know the three trees you are going to merge (the one "original" |
| tree, aka the common tree, and the two "result" trees, aka the branches |
| you want to merge), you do a "merge" read into the index. This will |
| complain if it has to throw away your old index contents, so you should |
| make sure that you've committed those - in fact you would normally |
| always do a merge against your last commit (which should thus match what |
| 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 |
| index file, and you can just write the result out with |
| <code class="literal">git-write-tree</code>.</p></div><div class="section" lang="en"><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 |
| been added.moved or removed, or if both branches have modified the |
| same file, you will be left with an index tree that contains "merge |
| entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree |
| object, and you will have to resolve any such merge clashes using |
| 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> |
| command. An example:</p><div class="literallayout"><p>$ git-read-tree -m $orig HEAD $target<br> |
| $ git-ls-files --unmerged<br> |
| 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c<br> |
| 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c<br> |
| 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c</p></div><p>Each line of the <code class="literal">git-ls-files —unmerged</code> output begins with |
| the blob mode bits, blob SHA1, <span class="emphasis"><em>stage number</em></span>, and the |
| filename. The <span class="emphasis"><em>stage number</em></span> is git's way to say which tree it |
| came from: stage 1 corresponds to <code class="literal">$orig</code> tree, stage 2 <code class="literal">HEAD</code> |
| tree, and stage3 <code class="literal">$target</code> tree.</p><p>Earlier we said that trivial merges are done inside |
| <code class="literal">git-read-tree -m</code>. For example, if the file did not change |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> nor <code class="literal">$target</code>, or if the file changed |
| from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way, |
| obviously the final outcome is what is in <code class="literal">HEAD</code>. What the |
| above example shows is that file <code class="literal">hello.c</code> was changed from |
| <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> in a different way. |
| You could resolve this by running your favorite 3-way merge |
| program, e.g. <code class="literal">diff3</code>, <code class="literal">merge</code>, or git's own merge-file, on |
| the blob objects from these three stages yourself, like this:</p><div class="literallayout"><p>$ git-cat-file blob 263414f... >hello.c~1<br> |
| $ git-cat-file blob 06fa6a2... >hello.c~2<br> |
| $ git-cat-file blob cc44c73... >hello.c~3<br> |
| $ 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 |
| with conflict markers if there are conflicts. After verifying |
| the merge result makes sense, you can tell git what the final |
| merge result for this file is by:</p><div class="literallayout"><p>$ mv -f hello.c~2 hello.c<br> |
| $ git-update-index hello.c</p></div><p>When a path is in unmerged state, running <code class="literal">git-update-index</code> for |
| that path tells git to mark the path resolved.</p><p>The above is the description of a git merge at the lowest level, |
| to help you understand what conceptually happens under the hood. |
| In practice, nobody, not even git itself, uses three <code class="literal">git-cat-file</code> |
| for this. There is <code class="literal">git-merge-index</code> program that extracts the |
| 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 class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="pack-files"></a>How git stores objects efficiently: pack files</h2></div></div></div><p>We've seen how git stores each object in a file named after the |
| object's SHA1 hash.</p><p>Unfortunately this system becomes inefficient once a project has a |
| lot of objects. Try this on an old project:</p><div class="literallayout"><p>$ git count-objects<br> |
| 6930 objects, 47620 kilobytes</p></div><p>The first number is the number of objects which are kept in |
| individual files. The second is the amount of space taken up by |
| those "loose" objects.</p><p>You can save space and make git faster by moving these loose objects in |
| to a "pack file", which stores a group of objects in an efficient |
| compressed format; the details of how pack files are formatted can be |
| found in <a 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> |
| Generating pack...<br> |
| Done counting 6020 objects.<br> |
| Deltifying 6020 objects.<br> |
| 100% (6020/6020) done<br> |
| Writing 6020 objects.<br> |
| 100% (6020/6020) done<br> |
| Total 6020, written 6020 (delta 4070), reused 0 (delta 0)<br> |
| 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 |
| pack. This will also remove any unreferenced objects (which may be |
| created when, for example, you use "git reset" to remove a commit). |
| You can verify that the loose objects are gone by looking at the |
| .git/objects directory or by running</p><div class="literallayout"><p>$ git count-objects<br> |
| 0 objects, 0 kilobytes</p></div><p>Although the object files are gone, any commands that refer to those |
| objects will work exactly as they did before.</p><p>The <a href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for |
| you, so is normally the only high-level command you need.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="dangling-objects"></a>Dangling objects</h2></div></div></div><p>The <a href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling |
| objects. They are not a problem.</p><p>The most common cause of dangling objects is that you've rebased a |
| branch, or you have pulled from somebody else who rebased a branch—see |
| <a 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 |
| branch still exists, as does everything it pointed to. The branch |
| pointer itself just doesn't, since you replaced it with another one.</p><p>There are also other situations that cause dangling objects. For |
| example, a "dangling blob" may arise because you did a "git add" of a |
| file, but then, before you actually committed it and made it part of the |
| bigger picture, you changed something else in that file and committed |
| that <span class="strong"><strong>updated</strong></span> thing - the old state that you added originally ends up |
| not being pointed to by any commit or tree, so it's now a dangling blob |
| object.</p><p>Similarly, when the "recursive" merge strategy runs, and finds that |
| there are criss-cross merges and thus more than one merge base (which is |
| fairly unusual, but it does happen), it will generate one temporary |
| midway tree (or possibly even more, if you had lots of criss-crossing |
| merges and more than two merge bases) as a temporary internal merge |
| base, and again, those are real objects, but the end result will not end |
| 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 |
| even be very useful: if you screw something up, the dangling objects can |
| be how you recover your old tree (say, you did a rebase, and realized |
| that you really didn't want to - you can look at what dangling objects |
| 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 |
| from any branch, tag, or other reference. If you decide it's something |
| 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 |
| 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 |
| what the "ls" for that directory was), and that may give you some idea |
| of what the operation was that left that dangling object.</p><p>Usually, dangling blobs and trees aren't very interesting. They're |
| almost always the result of either being a half-way mergebase (the blob |
| will often even have the conflict markers from a merge in it, if you |
| have had conflicting merges that you fixed up by hand), or simply |
| because you interrupted a "git fetch" with ^C or something like that, |
| leaving _some_ of the new objects in the object database, but just |
| dangling and useless.</p><p>Anyway, once you are sure that you're not interested in any dangling |
| 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 |
| repository - it's kind of like doing a filesystem fsck recovery: you |
| don't want to do that while the filesystem is mounted.</p><p>(The same is true of "git-fsck" itself, btw - but since |
| git-fsck never actually <span class="strong"><strong>changes</strong></span> the repository, it just reports |
| on what it found, git-fsck itself is never "dangerous" to run. |
| Running it while somebody is actually changing the repository can cause |
| confusing and scary messages, but it won't actually do anything bad. In |
| contrast, running "git prune" while somebody is actively changing the |
| repository is a <span class="strong"><strong>BAD</strong></span> idea).</p></div><div class="section" lang="en"><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 |
| source code. This section gives you a little guidance to show where to |
| 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 |
| today, but is small enough to read in one sitting.</p><p>Note that terminology has changed since that revision. For example, the |
| README in that revision uses the word "changeset" to describe what we |
| now call a <a href="#def_commit_object">commit</a>.</p><p>Also, we do not call it "cache" any more, but "index", however, the |
| file is still called <code class="literal">cache.h</code>. Remark: Not much reason to change it now, |
| especially since there is no good single name for it anyway, because it is |
| 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 |
| 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 |
| which were extremely simple, and which you used in scripts, piping the |
| output of one into another. This turned out to be good for initial |
| development, since it was easier to test new things. However, recently |
| many of these parts have become builtins, and some of the core has been |
| "libified", i.e. put into libgit.a for performance, portability reasons, |
| and to avoid code duplication.</p><p>By now, you know what the index is (and find the corresponding data |
| structures in <code class="literal">cache.h</code>), and that there are just a couple of object types |
| (blobs, trees, commits and tags) which inherit their common structure from |
| <code class="literal">struct object</code>, which is their first member (and thus, you can cast e.g. |
| <code class="literal">(struct object *)commit</code> to achieve the _same_ as <code class="literal">&commit->object</code>, i.e. |
| 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 href="#naming-commits" title="Naming commits">the section called “Naming commits”</a>. |
| There are quite a few ways to name an object (and not only revisions!). |
| All of these are handled in <code class="literal">sha1_name.c</code>. Just have a quick look at |
| the function <code class="literal">get_sha1()</code>. A lot of the special handling is done by |
| 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: |
| 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> |
| 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 |
| _always_ printed a list of revisions to stdout. It is still functional, |
| and needs to, since most new Git programs start out as scripts using |
| <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 |
| options that were relevant for the different plumbing commands that were |
| 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 |
| <code class="literal">revision.h</code>. It wraps the options in a struct named <code class="literal">rev_info</code>, which |
| 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 |
| <code class="literal">setup_revisions()</code>, which parses the revisions and the common command line |
| options for the revision walker. This information is stored in the struct |
| <code class="literal">rev_info</code> for later consumption. You can do your own command line option |
| parsing after calling <code class="literal">setup_revisions()</code>. After that, you have to call |
| <code class="literal">prepare_revision_walk()</code> for initialization, and then you can get the |
| 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, |
| just have a look at the first implementation of <code class="literal">cmd_log()</code>; call |
| <code class="literal">git-show v1.3.0<sub>155^2</sub>4</code> and scroll down to that function (note that you |
| 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 |
| command <code class="literal">git</code>. The source side of a builtin is</p><div class="itemizedlist"><ul type="disc"><li> |
| a function called <code class="literal">cmd_<bla></code>, typically defined in <code class="literal">builtin-<bla>.c</code>, |
| and declared in <code class="literal">builtin.h</code>, |
| </li><li> |
| an entry in the <code class="literal">commands[]</code> array in <code class="literal">git.c</code>, and |
| </li><li> |
| an entry in <code class="literal">BUILTIN_OBJECTS</code> in the <code class="literal">Makefile</code>. |
| </li></ul></div><p>Sometimes, more than one builtin is contained in one source file. For |
| example, <code class="literal">cmd_whatchanged()</code> and <code class="literal">cmd_log()</code> both reside in <code class="literal">builtin-log.c</code>, |
| since they share quite a bit of code. In that case, the commands which are |
| _not_ named like the <code class="literal">.c</code> file in which they live have to be listed in |
| <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, |
| 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 |
| 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 |
| access a blob just knowing the object name of it?". The first step is to |
| find a Git command with which you can do it. In this example, it is either |
| <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 type="disc"><li> |
| is plumbing, and |
| </li><li> |
| was around even in the initial commit (it literally went only through |
| some 20 revisions as <code class="literal">cat-file.c</code>, was renamed to <code class="literal">builtin-cat-file.c</code> |
| when made a builtin, and then saw less than 10 versions). |
| </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 |
| it does.</p><div class="literallayout"><p> git_config(git_default_config);<br> |
| if (argc != 3)<br> |
| usage("git-cat-file [-t|-s|-e|-p|<type>] <sha1>");<br> |
| if (get_sha1(argv[2], sha1))<br> |
| die("Not a valid object name %s", argv[2]);</p></div><p>Let's skip over the obvious details; the only really interesting part |
| here is the call to <code class="literal">get_sha1()</code>. It tries to interpret <code class="literal">argv[2]</code> as an |
| object name, and if it refers to an object which is present in the current |
| 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 type="disc"><li> |
| <code class="literal">get_sha1()</code> returns 0 on _success_. This might surprise some new |
| Git hackers, but there is a long tradition in UNIX to return different |
| negative numbers in case of different errors — and 0 on success. |
| </li><li> |
| the variable <code class="literal">sha1</code> in the function signature of <code class="literal">get_sha1()</code> is <code class="literal">unsigned |
| char *</code>, but is actually expected to be a pointer to <code class="literal">unsigned |
| char[20]</code>. This variable will contain the 160-bit SHA-1 of the given |
| commit. Note that whenever a SHA-1 is passed as <code class="literal">unsigned char *</code>, it |
| is the binary representation, as opposed to the ASCII representation in |
| hex characters, which is passed as <code class="literal">char *</code>. |
| </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> |
| 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 |
| object). To know how the function <code class="literal">read_object_with_reference()</code> actually |
| works, find the source code for it (something like <code class="literal">git grep |
| read_object_with | grep ":[a-z]"</code> in the git repository), and read |
| 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, |
| it helps to search through the output of <code class="literal">git log</code>, and then <code class="literal">git show</code> the |
| corresponding commit.</p><p>Example: If you know that there was some test case for <code class="literal">git bundle</code>, but |
| do not remember where it was (yes, you _could_ <code class="literal">git grep bundle t/</code>, but that |
| 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, |
| and see that it is in commit 18449ab0… Now just copy this object name, |
| 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 |
| 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 |
| itself!</p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="glossary"></a>Chapter 8. GIT Glossary</h2></div></div></div><div class="variablelist"><dl><dt><span class="term"> |
| <a name="def_alternate_object_database"></a>alternate object database |
| </span></dt><dd> |
| Via the alternates mechanism, a <a href="#def_repository">repository</a> |
| can inherit part of its <a href="#def_object_database">object database</a> |
| from another object database, which is called "alternate". |
| </dd><dt><span class="term"> |
| <a name="def_bare_repository"></a>bare repository |
| </span></dt><dd> |
| A bare repository is normally an appropriately |
| named <a href="#def_directory">directory</a> with a <code class="literal">.git</code> suffix that does not |
| have a locally checked-out copy of any of the files under |
| revision control. That is, all of the <code class="literal">git</code> |
| administrative and control files that would normally be present in the |
| hidden <code class="literal">.git</code> sub-directory are directly present in the |
| <code class="literal">repository.git</code> directory instead, |
| and no other files are present and checked out. Usually publishers of |
| public repositories make bare repositories available. |
| </dd><dt><span class="term"> |
| <a name="def_blob_object"></a>blob object |
| </span></dt><dd> |
| Untyped <a href="#def_object">object</a>, e.g. the contents of a file. |
| </dd><dt><span class="term"> |
| <a name="def_branch"></a>branch |
| </span></dt><dd> |
| A "branch" is an active line of development. The most recent |
| <a href="#def_commit">commit</a> on a branch is referred to as the tip of |
| that branch. The tip of the branch is referenced by a branch |
| <a href="#def_head">head</a>, which moves forward as additional development |
| is done on the branch. A single git |
| <a href="#def_repository">repository</a> can track an arbitrary number of |
| branches, but your <a href="#def_working_tree">working tree</a> is |
| associated with just one of them (the "current" or "checked out" |
| branch), and <a href="#def_HEAD">HEAD</a> points to that branch. |
| </dd><dt><span class="term"> |
| <a name="def_cache"></a>cache |
| </span></dt><dd> |
| Obsolete for: <a href="#def_index">index</a>. |
| </dd><dt><span class="term"> |
| <a name="def_chain"></a>chain |
| </span></dt><dd> |
| A list of objects, where each <a href="#def_object">object</a> in the list contains |
| a reference to its successor (for example, the successor of a |
| <a href="#def_commit">commit</a> could be one of its <a href="#def_parent">parents</a>). |
| </dd><dt><span class="term"> |
| <a name="def_changeset"></a>changeset |
| </span></dt><dd> |
| BitKeeper/cvsps speak for "<a href="#def_commit">commit</a>". Since git does not |
| store changes, but states, it really does not make sense to use the term |
| "changesets" with git. |
| </dd><dt><span class="term"> |
| <a name="def_checkout"></a>checkout |
| </span></dt><dd> |
| The action of updating the <a href="#def_working_tree">working tree</a> to a |
| <a href="#def_revision">revision</a> which was stored in the |
| <a href="#def_object_database">object database</a>. |
| </dd><dt><span class="term"> |
| <a name="def_cherry-picking"></a>cherry-picking |
| </span></dt><dd> |
| In <a href="#def_SCM">SCM</a> jargon, "cherry pick" means to choose a subset of |
| changes out of a series of changes (typically commits) and record them |
| as a new series of changes on top of different codebase. In GIT, this is |
| performed by "git cherry-pick" command to extract the change introduced |
| by an existing <a href="#def_commit">commit</a> and to record it based on the tip |
| of the current <a href="#def_branch">branch</a> as a new commit. |
| </dd><dt><span class="term"> |
| <a name="def_clean"></a>clean |
| </span></dt><dd> |
| A <a href="#def_working_tree">working tree</a> is clean, if it |
| corresponds to the <a href="#def_revision">revision</a> referenced by the current |
| <a href="#def_head">head</a>. Also see "<a href="#def_dirty">dirty</a>". |
| </dd><dt><span class="term"> |
| <a name="def_commit"></a>commit |
| </span></dt><dd><p> |
| As a noun: A single point in the |
| git history; the entire history of a project is represented as a |
| set of interrelated commits. The word "commit" is often |
| used by git in the same places other revision control systems |
| use the words "revision" or "version". Also used as a short |
| hand for <a href="#def_commit_object">commit object</a>. |
| </p><p>As a verb: The action of storing a new snapshot of the project's |
| state in the git history, by creating a new commit representing the current |
| state of the <a href="#def_index">index</a> and advancing <a href="#def_HEAD">HEAD</a> |
| to point at the new commit.</p></dd><dt><span class="term"> |
| <a name="def_commit_object"></a>commit object |
| </span></dt><dd> |
| An <a href="#def_object">object</a> which contains the information about a |
| particular <a href="#def_revision">revision</a>, such as <a href="#def_parent">parents</a>, committer, |
| author, date and the <a href="#def_tree_object">tree object</a> which corresponds |
| to the top <a href="#def_directory">directory</a> of the stored |
| revision. |
| </dd><dt><span class="term"> |
| <a name="def_core_git"></a>core git |
| </span></dt><dd> |
| Fundamental data structures and utilities of git. Exposes only limited |
| source code management tools. |
| </dd><dt><span class="term"> |
| <a name="def_DAG"></a>DAG |
| </span></dt><dd> |
| Directed acyclic graph. The <a href="#def_commit">commit</a> objects form a |
| directed acyclic graph, because they have parents (directed), and the |
| graph of commit objects is acyclic (there is no |
| <a href="#def_chain">chain</a> which begins and ends with the same |
| <a href="#def_object">object</a>). |
| </dd><dt><span class="term"> |
| <a name="def_dangling_object"></a>dangling object |
| </span></dt><dd> |
| An <a href="#def_unreachable_object">unreachable object</a> which is not |
| <a href="#def_reachable">reachable</a> even from other unreachable objects; a |
| dangling object has no references to it from any |
| reference or <a href="#def_object">object</a> in the <a href="#def_repository">repository</a>. |
| </dd><dt><span class="term"> |
| <a name="def_detached_HEAD"></a>detached HEAD |
| </span></dt><dd> |
| Normally the <a href="#def_HEAD">HEAD</a> stores the name of a |
| <a href="#def_branch">branch</a>. However, git also allows you to <a href="#def_checkout">check out</a> |
| an arbitrary <a href="#def_commit">commit</a> that isn't necessarily the tip of any |
| particular branch. In this case HEAD is said to be "detached". |
| </dd><dt><span class="term"> |
| <a name="def_dircache"></a>dircache |
| </span></dt><dd> |
| You are <span class="strong"><strong>waaaaay</strong></span> behind. See <a href="#def_index">index</a>. |
| </dd><dt><span class="term"> |
| <a name="def_directory"></a>directory |
| </span></dt><dd> |
| The list you get with "ls" :-) |
| </dd><dt><span class="term"> |
| <a name="def_dirty"></a>dirty |
| </span></dt><dd> |
| A <a href="#def_working_tree">working tree</a> is said to be "dirty" if |
| it contains modifications which have not been <a href="#def_commit">committed</a> to the current |
| <a href="#def_branch">branch</a>. |
| </dd><dt><span class="term"> |
| <a name="def_ent"></a>ent |
| </span></dt><dd> |
| Favorite synonym to "<a href="#def_tree-ish">tree-ish</a>" by some total geeks. See |
| <code class="literal">http://en.wikipedia.org/wiki/Ent_(Middle-earth)</code> for an in-depth |
| explanation. Avoid this term, not to confuse people. |
| </dd><dt><span class="term"> |
| <a name="def_evil_merge"></a>evil merge |
| </span></dt><dd> |
| An evil merge is a <a href="#def_merge">merge</a> that introduces changes that |
| do not appear in any <a href="#def_parent">parent</a>. |
| </dd><dt><span class="term"> |
| <a name="def_fast_forward"></a>fast forward |
| </span></dt><dd> |
| A fast-forward is a special type of <a href="#def_merge">merge</a> where you have a |
| <a href="#def_revision">revision</a> and you are "merging" another |
| <a href="#def_branch">branch</a>'s changes that happen to be a descendant of what |
| you have. In such these cases, you do not make a new <a href="#def_merge">merge</a> |
| <a href="#def_commit">commit</a> but instead just update to his |
| revision. This will happen frequently on a |
| <a href="#def_tracking_branch">tracking branch</a> of a remote |
| <a href="#def_repository">repository</a>. |
| </dd><dt><span class="term"> |
| <a name="def_fetch"></a>fetch |
| </span></dt><dd> |
| Fetching a <a href="#def_branch">branch</a> means to get the |
| branch's <a href="#def_head_ref">head ref</a> from a remote |
| <a href="#def_repository">repository</a>, to find out which objects are |
| missing from the local <a href="#def_object_database">object database</a>, |
| and to get them, too. See also <a href="git-fetch.html" target="_top">git-fetch(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_file_system"></a>file system |
| </span></dt><dd> |
| Linus Torvalds originally designed git to be a user space file system, |
| i.e. the infrastructure to hold files and directories. That ensured the |
| efficiency and speed of git. |
| </dd><dt><span class="term"> |
| <a name="def_git_archive"></a>git archive |
| </span></dt><dd> |
| Synonym for <a href="#def_repository">repository</a> (for arch people). |
| </dd><dt><span class="term"> |
| <a name="def_grafts"></a>grafts |
| </span></dt><dd> |
| Grafts enables two otherwise different lines of development to be joined |
| together by recording fake ancestry information for commits. This way |
| you can make git pretend the set of <a href="#def_parent">parents</a> a <a href="#def_commit">commit</a> has |
| is different from what was recorded when the commit was |
| created. Configured via the <code class="literal">.git/info/grafts</code> file. |
| </dd><dt><span class="term"> |
| <a name="def_hash"></a>hash |
| </span></dt><dd> |
| In git's context, synonym to <a href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_head"></a>head |
| </span></dt><dd> |
| A <a href="#def_ref">named reference</a> to the <a href="#def_commit">commit</a> at the tip of a |
| <a href="#def_branch">branch</a>. Heads are stored in |
| <code class="literal">$GIT_DIR/refs/heads/</code>, except when using packed refs. (See |
| <a href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>.) |
| </dd><dt><span class="term"> |
| <a name="def_HEAD"></a>HEAD |
| </span></dt><dd> |
| The current <a href="#def_branch">branch</a>. In more detail: Your <a href="#def_working_tree">working tree</a> is normally derived from the state of the tree |
| referred to by HEAD. HEAD is a reference to one of the |
| <a href="#def_head">heads</a> in your repository, except when using a |
| <a href="#def_detached_HEAD">detached HEAD</a>, in which case it may |
| reference an arbitrary commit. |
| </dd><dt><span class="term"> |
| <a name="def_head_ref"></a>head ref |
| </span></dt><dd> |
| A synonym for <a href="#def_head">head</a>. |
| </dd><dt><span class="term"> |
| <a name="def_hook"></a>hook |
| </span></dt><dd> |
| During the normal execution of several git commands, call-outs are made |
| to optional scripts that allow a developer to add functionality or |
| checking. Typically, the hooks allow for a command to be pre-verified |
| and potentially aborted, and allow for a post-notification after the |
| operation is done. The hook scripts are found in the |
| <code class="literal">$GIT_DIR/hooks/</code> directory, and are enabled by simply |
| making them executable. |
| </dd><dt><span class="term"> |
| <a name="def_index"></a>index |
| </span></dt><dd> |
| A collection of files with stat information, whose contents are stored |
| as objects. The index is a stored version of your |
| <a href="#def_working_tree">working tree</a>. Truth be told, it can also contain a second, and even |
| a third version of a working tree, which are used |
| when <a href="#def_merge">merging</a>. |
| </dd><dt><span class="term"> |
| <a name="def_index_entry"></a>index entry |
| </span></dt><dd> |
| The information regarding a particular file, stored in the |
| <a href="#def_index">index</a>. An index entry can be unmerged, if a |
| <a href="#def_merge">merge</a> was started, but not yet finished (i.e. if |
| the index contains multiple versions of that file). |
| </dd><dt><span class="term"> |
| <a name="def_master"></a>master |
| </span></dt><dd> |
| The default development <a href="#def_branch">branch</a>. Whenever you |
| create a git <a href="#def_repository">repository</a>, a branch named |
| "master" is created, and becomes the active branch. In most |
| cases, this contains the local development, though that is |
| purely by convention and is not required. |
| </dd><dt><span class="term"> |
| <a name="def_merge"></a>merge |
| </span></dt><dd><p> |
| As a verb: To bring the contents of another |
| <a href="#def_branch">branch</a> (possibly from an external |
| <a href="#def_repository">repository</a>) into the current branch. In the |
| case where the merged-in branch is from a different repository, |
| this is done by first <a href="#def_fetch">fetching</a> the remote branch |
| and then merging the result into the current branch. This |
| combination of fetch and merge operations is called a |
| <a href="#def_pull">pull</a>. Merging is performed by an automatic process |
| that identifies changes made since the branches diverged, and |
| then applies all those changes together. In cases where changes |
| conflict, manual intervention may be required to complete the |
| merge. |
| </p><p>As a noun: unless it is a <a href="#def_fast_forward">fast forward</a>, a |
| successful merge results in the creation of a new <a href="#def_commit">commit</a> |
| representing the result of the merge, and having as |
| <a href="#def_parent">parents</a> the tips of the merged <a href="#def_branch">branches</a>. |
| This commit is referred to as a "merge commit", or sometimes just a |
| "merge".</p></dd><dt><span class="term"> |
| <a name="def_object"></a>object |
| </span></dt><dd> |
| The unit of storage in git. It is uniquely identified by the |
| <a href="#def_SHA1">SHA1</a> of its contents. Consequently, an |
| object can not be changed. |
| </dd><dt><span class="term"> |
| <a name="def_object_database"></a>object database |
| </span></dt><dd> |
| Stores a set of "objects", and an individual <a href="#def_object">object</a> is |
| identified by its <a href="#def_object_name">object name</a>. The objects usually |
| live in <code class="literal">$GIT_DIR/objects/</code>. |
| </dd><dt><span class="term"> |
| <a name="def_object_identifier"></a>object identifier |
| </span></dt><dd> |
| Synonym for <a href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_object_name"></a>object name |
| </span></dt><dd> |
| The unique identifier of an <a href="#def_object">object</a>. The <a href="#def_hash">hash</a> |
| of the object's contents using the Secure Hash Algorithm |
| 1 and usually represented by the 40 character hexadecimal encoding of |
| the <a href="#def_hash">hash</a> of the object (possibly followed by |
| a white space). |
| </dd><dt><span class="term"> |
| <a name="def_object_type"></a>object type |
| </span></dt><dd> |
| One of the identifiers |
| "<a href="#def_commit">commit</a>","<a href="#def_tree">tree</a>","<a href="#def_tag">tag</a>" or "<a href="#def_blob_object">blob</a>" |
| describing the type of an <a href="#def_object">object</a>. |
| </dd><dt><span class="term"> |
| <a name="def_octopus"></a>octopus |
| </span></dt><dd> |
| To <a href="#def_merge">merge</a> more than two <a href="#def_branch">branches</a>. Also denotes an |
| intelligent predator. |
| </dd><dt><span class="term"> |
| <a name="def_origin"></a>origin |
| </span></dt><dd> |
| The default upstream <a href="#def_repository">repository</a>. Most projects have |
| at least one upstream project which they track. By default |
| <span class="emphasis"><em>origin</em></span> is used for that purpose. New upstream updates |
| will be fetched into remote <a href="#def_tracking_branch">tracking branches</a> named |
| origin/name-of-upstream-branch, which you can see using |
| "<code class="literal">git branch -r</code>". |
| </dd><dt><span class="term"> |
| <a name="def_pack"></a>pack |
| </span></dt><dd> |
| A set of objects which have been compressed into one file (to save space |
| or to transmit them efficiently). |
| </dd><dt><span class="term"> |
| <a name="def_pack_index"></a>pack index |
| </span></dt><dd> |
| The list of identifiers, and other information, of the objects in a |
| <a href="#def_pack">pack</a>, to assist in efficiently accessing the contents of a |
| pack. |
| </dd><dt><span class="term"> |
| <a name="def_parent"></a>parent |
| </span></dt><dd> |
| A <a href="#def_commit_object">commit object</a> contains a (possibly empty) list |
| of the logical predecessor(s) in the line of development, i.e. its |
| parents. |
| </dd><dt><span class="term"> |
| <a name="def_pickaxe"></a>pickaxe |
| </span></dt><dd> |
| The term <a href="#def_pickaxe">pickaxe</a> refers to an option to the diffcore |
| routines that help select changes that add or delete a given text |
| string. With the —pickaxe-all option, it can be used to view the full |
| <a href="#def_changeset">changeset</a> that introduced or removed, say, a |
| particular line of text. See <a href="git-diff.html" target="_top">git-diff(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_plumbing"></a>plumbing |
| </span></dt><dd> |
| Cute name for <a href="#def_core_git">core git</a>. |
| </dd><dt><span class="term"> |
| <a name="def_porcelain"></a>porcelain |
| </span></dt><dd> |
| Cute name for programs and program suites depending on |
| <a href="#def_core_git">core git</a>, presenting a high level access to |
| core git. Porcelains expose more of a <a href="#def_SCM">SCM</a> |
| interface than the <a href="#def_plumbing">plumbing</a>. |
| </dd><dt><span class="term"> |
| <a name="def_pull"></a>pull |
| </span></dt><dd> |
| Pulling a <a href="#def_branch">branch</a> means to <a href="#def_fetch">fetch</a> it and |
| <a href="#def_merge">merge</a> it. See also <a href="git-pull.html" target="_top">git-pull(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_push"></a>push |
| </span></dt><dd> |
| Pushing a <a href="#def_branch">branch</a> means to get the branch's |
| <a href="#def_head_ref">head ref</a> from a remote <a href="#def_repository">repository</a>, |
| find out if it is an ancestor to the branch's local |
| head ref is a direct, and in that case, putting all |
| objects, which are <a href="#def_reachable">reachable</a> from the local |
| head ref, and which are missing from the remote |
| repository, into the remote |
| <a href="#def_object_database">object database</a>, and updating the remote |
| head ref. If the remote <a href="#def_head">head</a> is not an |
| ancestor to the local head, the push fails. |
| </dd><dt><span class="term"> |
| <a name="def_reachable"></a>reachable |
| </span></dt><dd> |
| All of the ancestors of a given <a href="#def_commit">commit</a> are said to be |
| "reachable" from that commit. More |
| generally, one <a href="#def_object">object</a> is reachable from |
| another if we can reach the one from the other by a <a href="#def_chain">chain</a> |
| that follows <a href="#def_tag">tags</a> to whatever they tag, |
| <a href="#def_commit_object">commits</a> to their parents or trees, and |
| <a href="#def_tree_object">trees</a> to the trees or <a href="#def_blob_object">blobs</a> |
| that they contain. |
| </dd><dt><span class="term"> |
| <a name="def_rebase"></a>rebase |
| </span></dt><dd> |
| To reapply a series of changes from a <a href="#def_branch">branch</a> to a |
| different base, and reset the <a href="#def_head">head</a> of that branch |
| to the result. |
| </dd><dt><span class="term"> |
| <a name="def_ref"></a>ref |
| </span></dt><dd> |
| A 40-byte hex representation of a <a href="#def_SHA1">SHA1</a> or a name that |
| denotes a particular <a href="#def_object">object</a>. These may be stored in |
| <code class="literal">$GIT_DIR/refs/</code>. |
| </dd><dt><span class="term"> |
| <a name="def_reflog"></a>reflog |
| </span></dt><dd> |
| A reflog shows the local "history" of a ref. In other words, |
| it can tell you what the 3rd last revision in _this_ repository |
| was, and what was the current state in _this_ repository, |
| yesterday 9:14pm. See <a href="git-reflog.html" target="_top">git-reflog(1)</a> for details. |
| </dd><dt><span class="term"> |
| <a name="def_refspec"></a>refspec |
| </span></dt><dd> |
| A "refspec" is used by <a href="#def_fetch">fetch</a> and |
| <a href="#def_push">push</a> to describe the mapping between remote |
| <a href="#def_ref">ref</a> and local ref. They are combined with a colon in |
| the format <src>:<dst>, preceded by an optional plus sign, +. |
| For example: <code class="literal">git fetch $URL |
| refs/heads/master:refs/heads/origin</code> means "grab the master |
| <a href="#def_branch">branch</a> <a href="#def_head">head</a> from the $URL and store |
| it as my origin branch head". And <code class="literal">git push |
| $URL refs/heads/master:refs/heads/to-upstream</code> means "publish my |
| master branch head as to-upstream branch at $URL". See also |
| <a href="git-push.html" target="_top">git-push(1)</a> |
| </dd><dt><span class="term"> |
| <a name="def_repository"></a>repository |
| </span></dt><dd> |
| A collection of <a href="#def_ref">refs</a> together with an |
| <a href="#def_object_database">object database</a> containing all objects |
| which are <a href="#def_reachable">reachable</a> from the refs, possibly |
| accompanied by meta data from one or more <a href="#def_porcelain">porcelains</a>. A |
| repository can share an object database with other repositories |
| via <a href="#def_alternate_object_database">alternates mechanism</a>. |
| </dd><dt><span class="term"> |
| <a name="def_resolve"></a>resolve |
| </span></dt><dd> |
| The action of fixing up manually what a failed automatic |
| <a href="#def_merge">merge</a> left behind. |
| </dd><dt><span class="term"> |
| <a name="def_revision"></a>revision |
| </span></dt><dd> |
| A particular state of files and directories which was stored in the |
| <a href="#def_object_database">object database</a>. It is referenced by a |
| <a href="#def_commit_object">commit object</a>. |
| </dd><dt><span class="term"> |
| <a name="def_rewind"></a>rewind |
| </span></dt><dd> |
| To throw away part of the development, i.e. to assign the |
| <a href="#def_head">head</a> to an earlier <a href="#def_revision">revision</a>. |
| </dd><dt><span class="term"> |
| <a name="def_SCM"></a>SCM |
| </span></dt><dd> |
| Source code management (tool). |
| </dd><dt><span class="term"> |
| <a name="def_SHA1"></a>SHA1 |
| </span></dt><dd> |
| Synonym for <a href="#def_object_name">object name</a>. |
| </dd><dt><span class="term"> |
| <a name="def_shallow_repository"></a>shallow repository |
| </span></dt><dd> |
| A shallow <a href="#def_repository">repository</a> has an incomplete |
| history some of whose <a href="#def_commit">commits</a> have <a href="#def_parent">parents</a> cauterized away (in other |
| words, git is told to pretend that these commits do not have the |
| parents, even though they are recorded in the <a href="#def_commit_object">commit object</a>). This is sometimes useful when you are interested only in the |
| recent history of a project even though the real history recorded in the |
| upstream is much larger. A shallow repository |
| is created by giving the <code class="literal">—depth</code> option to <a href="git-clone.html" target="_top">git-clone(1)</a>, and |
| its history can be later deepened with <a href="git-fetch.html" target="_top">git-fetch(1)</a>. |
| </dd><dt><span class="term"> |
| <a name="def_symref"></a>symref |
| </span></dt><dd> |
| Symbolic reference: instead of containing the <a href="#def_SHA1">SHA1</a> |
| id itself, it is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when |
| referenced, it recursively dereferences to this reference. |
| <span class="emphasis"><em><a href="#def_HEAD">HEAD</a></em></span> is a prime example of a symref. Symbolic |
| references are manipulated with the <a href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a> |
| command. |
| </dd><dt><span class="term"> |
| <a name="def_tag"></a>tag |
| </span></dt><dd> |
| A <a href="#def_ref">ref</a> pointing to a <a href="#def_tag_object">tag</a> or |
| <a href="#def_commit_object">commit object</a>. In contrast to a <a href="#def_head">head</a>, |
| a tag is not changed by a <a href="#def_commit">commit</a>. Tags (not |
| <a href="#def_tag_object">tag objects</a>) are stored in <code class="literal">$GIT_DIR/refs/tags/</code>. A |
| git tag has nothing to do with a Lisp tag (which would be |
| called an <a href="#def_object_type">object type</a> in git's context). A |
| tag is most typically used to mark a particular point in the |
| commit ancestry <a href="#def_chain">chain</a>. |
| </dd><dt><span class="term"> |
| <a name="def_tag_object"></a>tag object |
| </span></dt><dd> |
| An <a href="#def_object">object</a> containing a <a href="#def_ref">ref</a> pointing to |
| another object, which can contain a message just like a |
| <a href="#def_commit_object">commit object</a>. It can also contain a (PGP) |
| signature, in which case it is called a "signed tag object". |
| </dd><dt><span class="term"> |
| <a name="def_topic_branch"></a>topic branch |
| </span></dt><dd> |
| A regular git <a href="#def_branch">branch</a> that is used by a developer to |
| identify a conceptual line of development. Since branches are very easy |
| and inexpensive, it is often desirable to have several small branches |
| that each contain very well defined concepts or small incremental yet |
| related changes. |
| </dd><dt><span class="term"> |
| <a name="def_tracking_branch"></a>tracking branch |
| </span></dt><dd> |
| A regular git <a href="#def_branch">branch</a> that is used to follow changes from |
| another <a href="#def_repository">repository</a>. A tracking |
| branch should not contain direct modifications or have local commits |
| made to it. A tracking branch can usually be |
| identified as the right-hand-side <a href="#def_ref">ref</a> in a Pull: |
| <a href="#def_refspec">refspec</a>. |
| </dd><dt><span class="term"> |
| <a name="def_tree"></a>tree |
| </span></dt><dd> |
| Either a <a href="#def_working_tree">working tree</a>, or a <a href="#def_tree_object">tree object</a> together with the dependent <a href="#def_blob_object">blob</a> and tree objects |
| (i.e. a stored representation of a working tree). |
| </dd><dt><span class="term"> |
| <a name="def_tree_object"></a>tree object |
| </span></dt><dd> |
| An <a href="#def_object">object</a> containing a list of file names and modes along |
| with refs to the associated blob and/or tree objects. A |
| <a href="#def_tree">tree</a> is equivalent to a <a href="#def_directory">directory</a>. |
| </dd><dt><span class="term"> |
| <a name="def_tree-ish"></a>tree-ish |
| </span></dt><dd> |
| A <a href="#def_ref">ref</a> pointing to either a <a href="#def_commit_object">commit object</a>, a <a href="#def_tree_object">tree object</a>, or a <a href="#def_tag_object">tag object</a> pointing to a tag or commit or tree object. |
| </dd><dt><span class="term"> |
| <a name="def_unmerged_index"></a>unmerged index |
| </span></dt><dd> |
| An <a href="#def_index">index</a> which contains unmerged |
| <a href="#def_index_entry">index entries</a>. |
| </dd><dt><span class="term"> |
| <a name="def_unreachable_object"></a>unreachable object |
| </span></dt><dd> |
| An <a href="#def_object">object</a> which is not <a href="#def_reachable">reachable</a> from a |
| <a href="#def_branch">branch</a>, <a href="#def_tag">tag</a>, or any other reference. |
| </dd><dt><span class="term"> |
| <a name="def_working_tree"></a>working tree |
| </span></dt><dd> |
| The tree of actual checked out files. The working tree is |
| normally equal to the <a href="#def_HEAD">HEAD</a> plus any local changes |
| that you have made but not yet committed. |
| </dd></dl></div></div><div class="appendix" lang="en"><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 |
| explain how these work in more detail.</p><div class="section" lang="en"><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> |
| $ cd project<br> |
| $ git init<br> |
| Initialized empty Git repository in .git/<br> |
| $ git add .<br> |
| $ git commit</p></div><p>From a remote repository:</p><div class="literallayout"><p>$ git clone git://example.com/pub/project.git<br> |
| $ cd project</p></div></div><div class="section" lang="en"><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> |
| $ git checkout test # switch working directory to branch "test"<br> |
| $ git branch new # create branch "new" starting at current HEAD<br> |
| $ git branch -d new # delete branch "new"</p></div><p>Instead of basing new branch on current HEAD (the default), use:</p><div class="literallayout"><p>$ git branch new test # branch named "test"<br> |
| $ git branch new v2.6.15 # tag named v2.6.15<br> |
| $ git branch new HEAD^ # commit before the most recent<br> |
| $ git branch new HEAD^^ # commit before that<br> |
| $ 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> |
| $ git branch -r # list<br> |
| origin/master<br> |
| origin/next<br> |
| ...<br> |
| $ git checkout -b masterwork origin/master</p></div><p>Fetch a branch from a different repository, and give it a new |
| name in your repository:</p><div class="literallayout"><p>$ git fetch git://example.com/project.git theirbranch:mybranch<br> |
| $ 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> |
| $ git remote # list remote repositories<br> |
| example<br> |
| origin<br> |
| $ git remote show example # get details<br> |
| * remote example<br> |
| URL: git://example.com/project.git<br> |
| Tracked remote branches<br> |
| master next ...<br> |
| $ git fetch example # update branches from example<br> |
| $ git branch -r # list all remote branches</p></div></div><div class="section" lang="en"><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> |
| $ git log # list all commits<br> |
| $ git log src/ # ...modifying src/<br> |
| $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15<br> |
| $ git log master..test # ...in branch test, not in branch master<br> |
| $ git log test..master # ...in branch master, but not in test<br> |
| $ git log test...master # ...in one branch, not in both<br> |
| $ git log -S'foo()' # ...where difference contain "foo()"<br> |
| $ git log --since="2 weeks ago"<br> |
| $ git log -p # show patches as well<br> |
| $ git show # most recent commit<br> |
| $ git diff v2.6.15..v2.6.16 # diff between two tagged versions<br> |
| $ git diff v2.6.15..HEAD # diff with current head<br> |
| $ git grep "foo()" # search working directory for "foo()"<br> |
| $ git grep v2.6.15 "foo()" # search old tree for "foo()"<br> |
| $ 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> |
| $ git bisect bad # current version is bad<br> |
| $ git bisect good v2.6.13-rc2 # last known good revision<br> |
| Bisecting: 675 revisions left to test after this<br> |
| # test here, then:<br> |
| $ git bisect good # if this revision is good, or<br> |
| $ git bisect bad # if this revision is bad.<br> |
| # repeat until done.</p></div></div><div class="section" lang="en"><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> |
| [user]<br> |
| name = Your Name Comes Here<br> |
| email = you@yourdomain.example.com<br> |
| EOF</p></div><p>Select file contents to include in the next commit, then make the |
| commit:</p><div class="literallayout"><p>$ git add a.txt # updated file<br> |
| $ git add b.txt # new file<br> |
| $ git rm c.txt # old file<br> |
| $ 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> |
| $ git commit -a # use latest content of all tracked files</p></div></div><div class="section" lang="en"><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> |
| $ git pull git://example.com/project.git master<br> |
| # fetch and merge in remote branch<br> |
| $ git pull . test # equivalent to git merge test</p></div></div><div class="section" lang="en"><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> |
| # in HEAD but not in origin<br> |
| $ git am mbox # import patches from the mailbox "mbox"</p></div><p>Fetch a branch in a different git repository, then merge into the |
| 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 |
| 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 |
| 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> |
| $ git push example test</p></div></div><div class="section" lang="en"><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" lang="en"><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: |
| - It must be readable in order, from beginning to end, by |
| someone intelligent with a basic grasp of the unix |
| commandline, but without any special knowledge of git. If |
| necessary, any other prerequisites should be specifically |
| mentioned as they arise. |
| - Whenever possible, section headings should clearly describe |
| the task they explain how to do, in language that requires |
| no more knowledge than necessary: for example, "importing |
| patches into a project" rather than "the git-am command"</p><p>Think about how to create a clear chapter dependency graph that will |
| allow people to get to important topics without necessarily reading |
| everything in between.</p><p>Scan Documentation/ for other stuff left out; in particular: |
| howto's |
| some of technical/? |
| hooks |
| list of commands in <a href="git.html" target="_top">git(1)</a></p><p>Scan email archives for other stuff left out</p><p>Scan man pages to see if any assume more background than this manual |
| provides.</p><p>Simplify beginning by suggesting disconnected head instead of |
| temporary branch creation?</p><p>Add more good examples. Entire sections of just cookbook examples |
| might be a good idea; maybe make an "advanced examples" section a |
| 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 |
| documentation.</p><p>Add a section on working with other version control systems, including |
| 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>git unpack-objects -r for recovery</p></div></div></body></html> |
