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<p>This text is a work in progress—highly subject to
change—and may not accurately describe any released
version of the Apache™ Subversion® software.
Bookmarking or otherwise referring others to this page is
probably not such a smart idea. Please visit
<a href="http://www.svnbook.com/">http://www.svnbook.com/</a>
for stable versions of this book.</p>
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<h2 class="title" style="clear: both"><a id="svn.branchmerge.tags"></a>Tags</h2>
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<p>
<a id="idm5582" class="indexterm"></a>
Another common version control concept is a tag. A tag is
just a <span class="quote">“<span class="quote">snapshot</span>”</span> of a project in time. In
Subversion, this idea already seems to be everywhere. Each
repository revision is exactly that—a snapshot of the
filesystem after each commit.</p>
<p>However, people often want to give more human-friendly names
to tags, such as <code class="literal">release-1.0</code>. And they want
to make snapshots of smaller subdirectories of the filesystem.
After all, it's not so easy to remember that release 1.0 of a
piece of software is a particular subdirectory of revision
4822.</p>
<div class="sect2">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.tags.mksimple"></a>Creating a Simple Tag</h3>
</div>
</div>
</div>
<p>Once again, <span class="command"><strong>svn copy</strong></span> comes to the
rescue. If you want to create a snapshot of
<code class="filename">/calc/trunk</code> exactly as it looks in the
<code class="literal">HEAD</code> revision, make a copy of it:</p>
<div class="informalexample">
<pre class="screen">
$ svn copy http://svn.example.com/repos/calc/trunk \
http://svn.example.com/repos/calc/tags/release-1.0 \
-m "Tagging the 1.0 release of the 'calc' project."
Committed revision 902.
</pre>
</div>
<p>This example assumes that a
<code class="filename">/calc/tags</code> directory already exists. (If
it doesn't, you can create it using <span class="command"><strong>svn
mkdir</strong></span>.) After the copy completes, the new
<code class="filename">release-1.0</code> directory is forever a
snapshot of how the <code class="filename">/trunk</code> directory
looked in the <code class="literal">HEAD</code> revision at the time you
made the copy. Of course, you might want to be more precise
about exactly which revision you copy, in case somebody else
may have committed changes to the project when you weren't
looking. So if you know that revision 901 of
<code class="filename">/calc/trunk</code> is exactly the snapshot you
want, you can specify it by passing <code class="option">-r 901</code> to
the <span class="command"><strong>svn copy</strong></span> command.</p>
<p>But wait a moment: isn't this tag creation procedure the
same procedure we used to create a branch? Yes, in fact, it
is. In Subversion, there's no difference between a tag and a
branch. Both are just ordinary directories that are created
by copying. Just as with branches, the only reason a copied
directory is a <span class="quote">“<span class="quote">tag</span>”</span> is because
<span class="emphasis"><em>humans</em></span> have decided to treat it that way:
as long as nobody ever commits to the directory, it forever
remains a snapshot. If people start committing to it, it
becomes a branch.</p>
<p>If you are administering a repository, there are two
approaches you can take to managing tags. The first approach
is <span class="quote">“<span class="quote">hands off</span>”</span>: as a matter of project policy,
decide where your tags will live, and make sure all users know
how to treat the directories they copy. (That is, make sure
they know not to commit to them.) The second approach is more
paranoid: you can use one of the access control scripts
provided with Subversion to prevent anyone from doing anything
but creating new copies in the tags area (see
<a class="xref" href="svn.serverconfig.html" title="Chapter 6. Server Configuration">Chapter 6, <em>Server Configuration</em></a>). The paranoid approach,
however, isn't usually necessary. If a user accidentally
commits a change to a tag directory, you can simply undo the
change as discussed in the previous section. This is version
control, after all!</p>
</div>
<div class="sect2">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="svn.branchmerge.tags.mkcomplex"></a>Creating a Complex Tag</h3>
</div>
</div>
</div>
<p>Sometimes you may want a <span class="quote">“<span class="quote">snapshot</span>”</span> that is
more complicated than a single directory at a single
revision.</p>
<p>For example, pretend your project is much larger than our
<code class="filename">calc</code> example: suppose it contains a
number of subdirectories and many more files. In the course
of your work, you may decide that you need to create a working
copy that is designed to have specific features and bug fixes.
You can accomplish this by selectively backdating files or
directories to particular revisions (using <span class="command"><strong>svn
update</strong></span> with the <code class="option">-r</code> option
liberally), by switching files and directories to particular
branches (making use of <span class="command"><strong>svn switch</strong></span>), or
even just by making a bunch of local changes. When you're
done, your working copy is a hodgepodge of repository
locations from different revisions. But after testing, you
know it's the precise combination of data you need to
tag.</p>
<p>Time to make a snapshot. Copying one URL to another won't
work here. In this case, you want to make a snapshot of your
exact working copy arrangement and store it in the repository.
Luckily, <span class="command"><strong>svn copy</strong></span> actually has four
different uses (see <a class="xref" href="svn.ref.svn.c.copy.html" title="svn copy (cp)">svn copy (cp)</a> in <a class="xref" href="svn.ref.svn.html" title="svn Reference—Subversion Command-Line Client">svn Reference—Subversion Command-Line Client</a>), including the ability to copy a
working copy tree to the repository:</p>
<div class="informalexample">
<pre class="screen">
$ ls
my-working-copy/
$ svn copy my-working-copy \
http://svn.example.com/repos/calc/tags/mytag \
-m "Tag my existing working copy state."
Committed revision 940.
</pre>
</div>
<p>Now there is a new directory in the repository,
<code class="filename">/calc/tags/mytag</code>, which is an exact
snapshot of your working copy—mixed revisions, URLs,
local changes, and all.</p>
<p>Other users have found interesting uses for this feature.
Sometimes there are situations where you have a bunch of local
changes made to your working copy, and you'd like a
collaborator to see them. Instead of running <span class="command"><strong>svn
diff</strong></span> and sending a patch file (which won't capture
directory or symlink changes), you can
use <span class="command"><strong>svn copy</strong></span> to <span class="quote">“<span class="quote">upload</span>”</span> your
working copy to a private area of the repository. Your
collaborator can then either check out a verbatim copy of your
working copy or use <span class="command"><strong>svn merge</strong></span> to receive
your exact changes.</p>
<p>While this is a nice method for uploading a quick snapshot
of your working copy, note that this is <span class="emphasis"><em>not</em></span>
a good way to initially create a branch. Branch creation should
be an event unto itself, and this method conflates the creation
of a branch with extra changes to files, all within a single revision.
This makes it very difficult (later on) to identify a single
revision number as a branch point.</p>
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<p>You are reading <em>Version Control with Subversion</em> (for
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