cvs-migration.html - external/gitster/git-htmldocs - Git at Google

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 </style>
 <title>git for CVS users</title>
 </head>
 <body>
 <div id="header">
 <h1>git for CVS users</h1>
 </div>
 <div id="preamble">
 <div class="sectionbody">
 <p>Ok, so you're a CVS user. That's ok, it's a treatable condition, and the
 first step to recovery is admitting you have a problem. The fact that
 you are reading this file means that you may be well on that path
 already.</p>
 <p>The thing about CVS is that it absolutely sucks as a source control
 manager, and you'll thus be happy with almost anything else. git,
 however, may be a bit <em>too</em> different (read: "good") for your taste, and
 does a lot of things differently.</p>
 <p>One particular suckage of CVS is very hard to work around: CVS is
 basically a tool for tracking <em>file</em> history, while git is a tool for
 tracking <em>project</em> history. This sometimes causes problems if you are
 used to doing very strange things in CVS, in particular if you're doing
 things like making branches of just a subset of the project. git can't
 track that, since git never tracks things on the level of an individual
 file, only on the whole project level.</p>
 <p>The good news is that most people don't do that, and in fact most sane
 people think it's a bug in CVS that makes it tag (and check in changes)
 one file at a time. So most projects you'll ever see will use CVS
 <em>as if</em> it was sane. In which case you'll find it very easy indeed to
 move over to git.</p>
 <p>First off: this is not a git tutorial. See
 <a href="tutorial.html">Documentation/tutorial.txt</a> for how git
 actually works. This is more of a random collection of gotcha's
 and notes on converting from CVS to git.</p>
 <p>Second: CVS has the notion of a "repository" as opposed to the thing
 that you're actually working in (your working directory, or your
 "checked out tree"). git does not have that notion at all, and all git
 working directories <em>are</em> the repositories. However, you can easily
 emulate the CVS model by having one special "global repository", which
 people can synchronize with. See details later, but in the meantime
 just keep in mind that with git, every checked out working tree will
 have a full revision control history of its own.</p>
 </div>
 </div>
 <h2>Importing a CVS archive</h2>
 <div class="sectionbody">
 <p>Ok, you have an old project, and you want to at least give git a chance
 to see how it performs. The first thing you want to do (after you've
 gone through the git tutorial, and generally familiarized yourself with
 how to commit stuff etc in git) is to create a git'ified version of your
 CVS archive.</p>
 <p>Happily, that's very easy indeed. git will do it for you, although git
 will need the help of a program called "cvsps":</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>http://www.cobite.com/cvsps/</tt></pre>
 </div></div>
 <p>which is not actually related to git at all, but which makes CVS usage
 look almost sane (ie you almost certainly want to have it even if you
 decide to stay with CVS). However, git will want <em>at least</em> version 2.1
 of cvsps (available at the address above), and in fact will currently
 refuse to work with anything else.</p>
 <p>Once you've gotten (and installed) cvsps, you may or may not want to get
 any more familiar with it, but make sure it is in your path. After that,
 the magic command line is</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>git cvsimport -v -d &lt;cvsroot&gt; -C &lt;destination&gt; &lt;module&gt;</tt></pre>
 </div></div>
 <p>which will do exactly what you'd think it does: it will create a git
 archive of the named CVS module. The new archive will be created in the
 subdirectory named &lt;destination&gt;; it'll be created if it doesn't exist.
 Default is the local directory.</p>
 <p>It can take some time to actually do the conversion for a large archive
 since it involves checking out from CVS every revision of every file,
 and the conversion script is reasonably chatty unless you omit the <em>-v</em>
 option, but on some not very scientific tests it averaged about twenty
 revisions per second, so a medium-sized project should not take more
 than a couple of minutes. For larger projects or remote repositories,
 the process may take longer.</p>
 <p>After the (initial) import is done, the CVS archive's current head
 revision will be checked out &#8212; thus, you can start adding your own
 changes right away.</p>
 <p>The import is incremental, i.e. if you call it again next month it'll
 fetch any CVS updates that have been happening in the meantime. The
 cut-off is date-based, so don't change the branches that were imported
 from CVS.</p>
 <p>You can merge those updates (or, in fact, a different CVS branch) into
 your main branch:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>git resolve HEAD origin "merge with current CVS HEAD"</tt></pre>
 </div></div>
 <p>The HEAD revision from CVS is named "origin", not "HEAD", because git
 already uses "HEAD". (If you don't like <em>origin</em>, use cvsimport's
 <em>-o</em> option to change it.)</p>
 </div>
 <h2>Emulating CVS behaviour</h2>
 <div class="sectionbody">
 <p>So, by now you are convinced you absolutely want to work with git, but
 at the same time you absolutely have to have a central repository.
 Step back and think again. Okay, you still need a single central
 repository? There are several ways to go about that:</p>
 <ol>
 <li>
 <p>
 Designate a person responsible to pull all branches. Make the
 repository of this person public, and make every team member
 pull regularly from it.
 </p>
 </li>
 <li>
 <p>
 Set up a public repository with read/write access for every team
 member. Use "git pull/push" as you used "cvs update/commit". Be
 sure that your repository is up to date before pushing, just
 like you used to do with "cvs commit"; your push will fail if
 what you are pushing is not up to date.
 </p>
 </li>
 <li>
 <p>
 Make the repository of every team member public. It is the
 responsibility of each single member to pull from every other
 team member.
 </p>
 </li>
 </ol>
 </div>
 <h2>CVS annotate</h2>
 <div class="sectionbody">
 <p>So, something has gone wrong, and you don't know whom to blame, and
 you're an ex-CVS user and used to do "cvs annotate" to see who caused
 the breakage. You're looking for the "git annotate", and it's just
 claiming not to find such a script. You're annoyed.</p>
 <p>Yes, that's right. Core git doesn't do "annotate", although it's
 technically possible, and there are at least two specialized scripts out
 there that can be used to get equivalent information (see the git
 mailing list archives for details).</p>
 <p>git has a couple of alternatives, though, that you may find sufficient
 or even superior depending on your use. One is called "git-whatchanged"
 (for obvious reasons) and the other one is called "pickaxe" ("a tool for
 the software archaeologist").</p>
 <p>The "git-whatchanged" script is a truly trivial script that can give you
 a good overview of what has changed in a file or a directory (or an
 arbitrary list of files or directories). The "pickaxe" support is an
 additional layer that can be used to further specify exactly what you're
 looking for, if you already know the specific area that changed.</p>
 <p>Let's step back a bit and think about the reason why you would
 want to do "cvs annotate a-file.c" to begin with.</p>
 <p>You would use "cvs annotate" on a file when you have trouble
 with a function (or even a single "if" statement in a function)
 that happens to be defined in the file, which does not do what
 you want it to do. And you would want to find out why it was
 written that way, because you are about to modify it to suit
 your needs, and at the same time you do not want to break its
 current callers. For that, you are trying to find out why the
 original author did things that way in the original context.</p>
 <p>Many times, it may be enough to see the commit log messages of
 commits that touch the file in question, possibly along with the
 patches themselves, like this:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>$ git-whatchanged -p a-file.c</tt></pre>
 </div></div>
 <p>This will show log messages and patches for each commit that
 touches a-file.</p>
 <p>This, however, may not be very useful when this file has many
 modifications that are not related to the piece of code you are
 interested in. You would see many log messages and patches that
 do not have anything to do with the piece of code you are
 interested in. As an example, assuming that you have this piece
 of code that you are interested in in the HEAD version:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>if (frotz) {
  nitfol();
 }</tt></pre>
 </div></div>
 <p>you would use git-rev-list and git-diff-tree like this:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>$ git-rev-list HEAD |
  git-diff-tree --stdin -v -p -S'if (frotz) {
  nitfol();
 }'</tt></pre>
 </div></div>
 <p>We have already talked about the "--stdin" form of git-diff-tree
 command that reads the list of commits and compares each commit
 with its parents (otherwise you should go back and read the tutorial).
 The git-whatchanged command internally runs
 the equivalent of the above command, and can be used like this:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>$ git-whatchanged -p -S'if (frotz) {
  nitfol();
 }'</tt></pre>
 </div></div>
 <p>When the -S option is used, git-diff-tree command outputs
 differences between two commits only if one tree has the
 specified string in a file and the corresponding file in the
 other tree does not. The above example looks for a commit that
 has the "if" statement in it in a file, but its parent commit
 does not have it in the same shape in the corresponding file (or
 the other way around, where the parent has it and the commit
 does not), and the differences between them are shown, along
 with the commit message (thanks to the -v flag). It does not
 show anything for commits that do not touch this "if" statement.</p>
 <p>Also, in the original context, the same statement might have
 appeared at first in a different file and later the file was
 renamed to "a-file.c". CVS annotate would not help you to go
 back across such a rename, but git would still help you in such
 a situation. For that, you can give the -C flag to
 git-diff-tree, like this:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>$ git-whatchanged -p -C -S'if (frotz) {
  nitfol();
 }'</tt></pre>
 </div></div>
 <p>When the -C flag is used, file renames and copies are followed.
 So if the "if" statement in question happens to be in "a-file.c"
 in the current HEAD commit, even if the file was originally
 called "o-file.c" and then renamed in an earlier commit, or if
 the file was created by copying an existing "o-file.c" in an
 earlier commit, you will not lose track. If the "if" statement
 did not change across such a rename or copy, then the commit that
 does rename or copy would not show in the output, and if the
 "if" statement was modified while the file was still called
 "o-file.c", it would find the commit that changed the statement
 when it was in "o-file.c".</p>
 <div class="admonitionblock">
 <table><tr>
 <td class="icon">
 <div class="title">Note</div>
 </td>
 <td class="content">The current version of "git-diff-tree -C" is not eager
  enough to find copies, and it will miss the fact that a-file.c
  was created by copying o-file.c unless o-file.c was somehow
  changed in the same commit.</td>
 </tr></table>
 </div>
 <p>You can use the &#8212;pickaxe-all flag in addition to the -S flag.
 This causes the differences from all the files contained in
 those two commits, not just the differences between the files
 that contain this changed "if" statement:</p>
 <div class="literalblock">
 <div class="content">
 <pre><tt>$ git-whatchanged -p -C -S'if (frotz) {
  nitfol();
 }' --pickaxe-all</tt></pre>
 </div></div>
 <div class="admonitionblock">
 <table><tr>
 <td class="icon">
 <div class="title">Note</div>
 </td>
 <td class="content">This option is called "&#8212;pickaxe-all" because -S
  option is internally called "pickaxe", a tool for software
  archaeologists.</td>
 </tr></table>
 </div>
 </div>
 <div id="footer">
 <div id="footer-text">
 Last updated 06-Jan-2006 17:12:56 PDT
 </div>
 </div>
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	<title>git for CVS users</title>
	</head>
	<body>
	<div id="header">
	<h1>git for CVS users</h1>
	</div>
	<div id="preamble">
	<div class="sectionbody">
	<p>Ok, so you're a CVS user. That's ok, it's a treatable condition, and the
	first step to recovery is admitting you have a problem. The fact that
	you are reading this file means that you may be well on that path
	already.</p>
	<p>The thing about CVS is that it absolutely sucks as a source control
	manager, and you'll thus be happy with almost anything else. git,
	however, may be a bit <em>too</em> different (read: "good") for your taste, and
	does a lot of things differently.</p>
	<p>One particular suckage of CVS is very hard to work around: CVS is
	basically a tool for tracking <em>file</em> history, while git is a tool for
	tracking <em>project</em> history. This sometimes causes problems if you are
	used to doing very strange things in CVS, in particular if you're doing
	things like making branches of just a subset of the project. git can't
	track that, since git never tracks things on the level of an individual
	file, only on the whole project level.</p>
	<p>The good news is that most people don't do that, and in fact most sane
	people think it's a bug in CVS that makes it tag (and check in changes)
	one file at a time. So most projects you'll ever see will use CVS
	<em>as if</em> it was sane. In which case you'll find it very easy indeed to
	move over to git.</p>
	<p>First off: this is not a git tutorial. See
	<a href="tutorial.html">Documentation/tutorial.txt</a> for how git
	actually works. This is more of a random collection of gotcha's
	and notes on converting from CVS to git.</p>
	<p>Second: CVS has the notion of a "repository" as opposed to the thing
	that you're actually working in (your working directory, or your
	"checked out tree"). git does not have that notion at all, and all git
	working directories <em>are</em> the repositories. However, you can easily
	emulate the CVS model by having one special "global repository", which
	people can synchronize with. See details later, but in the meantime
	just keep in mind that with git, every checked out working tree will
	have a full revision control history of its own.</p>
	</div>
	</div>
	<h2>Importing a CVS archive</h2>
	<div class="sectionbody">
	<p>Ok, you have an old project, and you want to at least give git a chance
	to see how it performs. The first thing you want to do (after you've
	gone through the git tutorial, and generally familiarized yourself with
	how to commit stuff etc in git) is to create a git'ified version of your
	CVS archive.</p>
	<p>Happily, that's very easy indeed. git will do it for you, although git
	will need the help of a program called "cvsps":</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>http://www.cobite.com/cvsps/</tt></pre>
	</div></div>
	<p>which is not actually related to git at all, but which makes CVS usage
	look almost sane (ie you almost certainly want to have it even if you
	decide to stay with CVS). However, git will want <em>at least</em> version 2.1
	of cvsps (available at the address above), and in fact will currently
	refuse to work with anything else.</p>
	<p>Once you've gotten (and installed) cvsps, you may or may not want to get
	any more familiar with it, but make sure it is in your path. After that,
	the magic command line is</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>git cvsimport -v -d <cvsroot> -C <destination> <module></tt></pre>
	</div></div>
	<p>which will do exactly what you'd think it does: it will create a git
	archive of the named CVS module. The new archive will be created in the
	subdirectory named <destination>; it'll be created if it doesn't exist.
	Default is the local directory.</p>
	<p>It can take some time to actually do the conversion for a large archive
	since it involves checking out from CVS every revision of every file,
	and the conversion script is reasonably chatty unless you omit the <em>-v</em>
	option, but on some not very scientific tests it averaged about twenty
	revisions per second, so a medium-sized project should not take more
	than a couple of minutes. For larger projects or remote repositories,
	the process may take longer.</p>
	<p>After the (initial) import is done, the CVS archive's current head
	revision will be checked out — thus, you can start adding your own
	changes right away.</p>
	<p>The import is incremental, i.e. if you call it again next month it'll
	fetch any CVS updates that have been happening in the meantime. The
	cut-off is date-based, so don't change the branches that were imported
	from CVS.</p>
	<p>You can merge those updates (or, in fact, a different CVS branch) into
	your main branch:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>git resolve HEAD origin "merge with current CVS HEAD"</tt></pre>
	</div></div>
	<p>The HEAD revision from CVS is named "origin", not "HEAD", because git
	already uses "HEAD". (If you don't like <em>origin</em>, use cvsimport's
	<em>-o</em> option to change it.)</p>
	</div>
	<h2>Emulating CVS behaviour</h2>
	<div class="sectionbody">
	<p>So, by now you are convinced you absolutely want to work with git, but
	at the same time you absolutely have to have a central repository.
	Step back and think again. Okay, you still need a single central
	repository? There are several ways to go about that:</p>
	<ol>
	<li>
	<p>
	Designate a person responsible to pull all branches. Make the
	repository of this person public, and make every team member
	pull regularly from it.
	</p>
	</li>
	<li>
	<p>
	Set up a public repository with read/write access for every team
	member. Use "git pull/push" as you used "cvs update/commit". Be
	sure that your repository is up to date before pushing, just
	like you used to do with "cvs commit"; your push will fail if
	what you are pushing is not up to date.
	</p>
	</li>
	<li>
	<p>
	Make the repository of every team member public. It is the
	responsibility of each single member to pull from every other
	team member.
	</p>
	</li>
	</ol>
	</div>
	<h2>CVS annotate</h2>
	<div class="sectionbody">
	<p>So, something has gone wrong, and you don't know whom to blame, and
	you're an ex-CVS user and used to do "cvs annotate" to see who caused
	the breakage. You're looking for the "git annotate", and it's just
	claiming not to find such a script. You're annoyed.</p>
	<p>Yes, that's right. Core git doesn't do "annotate", although it's
	technically possible, and there are at least two specialized scripts out
	there that can be used to get equivalent information (see the git
	mailing list archives for details).</p>
	<p>git has a couple of alternatives, though, that you may find sufficient
	or even superior depending on your use. One is called "git-whatchanged"
	(for obvious reasons) and the other one is called "pickaxe" ("a tool for
	the software archaeologist").</p>
	<p>The "git-whatchanged" script is a truly trivial script that can give you
	a good overview of what has changed in a file or a directory (or an
	arbitrary list of files or directories). The "pickaxe" support is an
	additional layer that can be used to further specify exactly what you're
	looking for, if you already know the specific area that changed.</p>
	<p>Let's step back a bit and think about the reason why you would
	want to do "cvs annotate a-file.c" to begin with.</p>
	<p>You would use "cvs annotate" on a file when you have trouble
	with a function (or even a single "if" statement in a function)
	that happens to be defined in the file, which does not do what
	you want it to do. And you would want to find out why it was
	written that way, because you are about to modify it to suit
	your needs, and at the same time you do not want to break its
	current callers. For that, you are trying to find out why the
	original author did things that way in the original context.</p>
	<p>Many times, it may be enough to see the commit log messages of
	commits that touch the file in question, possibly along with the
	patches themselves, like this:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>$ git-whatchanged -p a-file.c</tt></pre>
	</div></div>
	<p>This will show log messages and patches for each commit that
	touches a-file.</p>
	<p>This, however, may not be very useful when this file has many
	modifications that are not related to the piece of code you are
	interested in. You would see many log messages and patches that
	do not have anything to do with the piece of code you are
	interested in. As an example, assuming that you have this piece
	of code that you are interested in in the HEAD version:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>if (frotz) {
	nitfol();
	}</tt></pre>
	</div></div>
	<p>you would use git-rev-list and git-diff-tree like this:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>$ git-rev-list HEAD \|
	git-diff-tree --stdin -v -p -S'if (frotz) {
	nitfol();
	}'</tt></pre>
	</div></div>
	<p>We have already talked about the "--stdin" form of git-diff-tree
	command that reads the list of commits and compares each commit
	with its parents (otherwise you should go back and read the tutorial).
	The git-whatchanged command internally runs
	the equivalent of the above command, and can be used like this:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>$ git-whatchanged -p -S'if (frotz) {
	nitfol();
	}'</tt></pre>
	</div></div>
	<p>When the -S option is used, git-diff-tree command outputs
	differences between two commits only if one tree has the
	specified string in a file and the corresponding file in the
	other tree does not. The above example looks for a commit that
	has the "if" statement in it in a file, but its parent commit
	does not have it in the same shape in the corresponding file (or
	the other way around, where the parent has it and the commit
	does not), and the differences between them are shown, along
	with the commit message (thanks to the -v flag). It does not
	show anything for commits that do not touch this "if" statement.</p>
	<p>Also, in the original context, the same statement might have
	appeared at first in a different file and later the file was
	renamed to "a-file.c". CVS annotate would not help you to go
	back across such a rename, but git would still help you in such
	a situation. For that, you can give the -C flag to
	git-diff-tree, like this:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>$ git-whatchanged -p -C -S'if (frotz) {
	nitfol();
	}'</tt></pre>
	</div></div>
	<p>When the -C flag is used, file renames and copies are followed.
	So if the "if" statement in question happens to be in "a-file.c"
	in the current HEAD commit, even if the file was originally
	called "o-file.c" and then renamed in an earlier commit, or if
	the file was created by copying an existing "o-file.c" in an
	earlier commit, you will not lose track. If the "if" statement
	did not change across such a rename or copy, then the commit that
	does rename or copy would not show in the output, and if the
	"if" statement was modified while the file was still called
	"o-file.c", it would find the commit that changed the statement
	when it was in "o-file.c".</p>
	<div class="admonitionblock">
	<table><tr>
	<td class="icon">
	<div class="title">Note</div>
	</td>
	<td class="content">The current version of "git-diff-tree -C" is not eager
	enough to find copies, and it will miss the fact that a-file.c
	was created by copying o-file.c unless o-file.c was somehow
	changed in the same commit.</td>
	</tr></table>
	</div>
	<p>You can use the —pickaxe-all flag in addition to the -S flag.
	This causes the differences from all the files contained in
	those two commits, not just the differences between the files
	that contain this changed "if" statement:</p>
	<div class="literalblock">
	<div class="content">
	<pre><tt>$ git-whatchanged -p -C -S'if (frotz) {
	nitfol();
	}' --pickaxe-all</tt></pre>
	</div></div>
	<div class="admonitionblock">
	<table><tr>
	<td class="icon">
	<div class="title">Note</div>
	</td>
	<td class="content">This option is called "—pickaxe-all" because -S
	option is internally called "pickaxe", a tool for software
	archaeologists.</td>
	</tr></table>
	</div>
	</div>
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	Last updated 06-Jan-2006 17:12:56 PDT
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