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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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<th colspan="3" align="center">Traversing Branches</th>
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<th width="60%" align="center">Chapter 4. Branching and Merging</th>
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<div class="sect1" title="Traversing Branches">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="svn.branchmerge.switchwc"></a>Traversing Branches</h2>
</div>
</div>
</div>
<p>The <span class="command"><strong>svn switch</strong></span> command transforms an
existing working copy to reflect a different branch. While this
command isn't strictly necessary for working with branches, it
provides a nice shortcut. In one of our earlier examples,
after creating your private branch, you checked out a fresh
working copy of the new repository directory. Instead, you can
simply ask Subversion to change your working copy of
<code class="filename">/calc/trunk</code> to mirror the new branch
location:</p>
<div class="informalexample">
<pre class="screen">
$ cd calc
$ svn info | grep URL
URL: http://svn.example.com/repos/calc/trunk
$ svn switch ^/calc/branches/my-calc-branch
U integer.c
U button.c
U Makefile
Updated to revision 341.
$ svn info | grep URL
URL: http://svn.example.com/repos/calc/branches/my-calc-branch
</pre>
</div>
<p><span class="quote">“<span class="quote">Switching</span>”</span> a working copy that has no local
modifications to a different branch results in the working copy
looking just as it would if you'd done a fresh checkout of the
directory. It's usually more efficient to
use this command, because often branches differ by only a small
degree. The server sends only the minimal set of changes
necessary to make your working copy reflect the branch
directory.</p>
<p>The <span class="command"><strong>svn switch</strong></span> command also takes a
<code class="option">--revision</code> (<code class="option">-r</code>) option, so you
need not always move your working copy to the
<code class="literal">HEAD</code> of the branch.</p>
<p>Of course, most projects are more complicated than our
<code class="filename">calc</code> example, and contain multiple
subdirectories. Subversion users often follow a specific
algorithm when using branches:</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>Copy the project's entire <span class="quote">“<span class="quote">trunk</span>”</span> to a new
branch directory.</p>
</li>
<li class="listitem">
<p>Switch only <span class="emphasis"><em>part</em></span> of the trunk
working copy to mirror the branch.</p>
</li>
</ol>
</div>
<p>In other words, if a user knows that the branch work needs
to happen on only a specific subdirectory, she uses
<span class="command"><strong>svn switch</strong></span> to move only that subdirectory to
the branch. (Or sometimes users will switch just a single
working file to the branch!) That way, the user can continue to
receive normal <span class="quote">“<span class="quote">trunk</span>”</span> updates to most of her
working copy, but the switched portions will remain immune
(unless someone commits a change to her branch). This feature
adds a whole new dimension to the concept of a <span class="quote">“<span class="quote">mixed
working copy</span>”</span>—not only can working copies contain a
mixture of working revisions, but they can also contain a
mixture of repository locations as well.</p>
<div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Typically switched subdirectories share common ancestry with
the location which is switched <span class="quote">“<span class="quote">away</span>”</span> from. However
<span class="command"><strong>svn switch</strong></span> can switch a subdirectory to mirror
a repository location which it shares no common ancestry with.
To do this you need to use the
<code class="option">--ignore-ancestry</code> option.
</p>
</td>
</tr>
</table>
</div>
<p>If your working copy contains a number of switched subtrees
from different repository locations, it continues to function as
normal. When you update, you'll receive patches to each subtree
as appropriate. When you commit, your local changes are still
applied as a single, atomic change to the repository.</p>
<p>Note that while it's okay for your working copy to reflect a
mixture of repository locations, these locations must all be
within the <span class="emphasis"><em>same</em></span> repository. Subversion
repositories aren't yet able to communicate with one another;
that feature is planned for the
future.<sup>[<a id="idp12808112" href="#ftn.idp12808112" class="footnote">43</a>]</sup></p>
<div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Administrators who need to change the URL of a repository
which is accessed via HTTP are encouraged to add to
their <code class="filename">httpd.conf</code> configuration file a
permanent redirect from the old URL location to the new one
(via the <code class="literal">RedirectPermanent</code> directive).
Subversion clients will generally display the new repository
URL in error messages generated when the user attempts to use
working copies which still reflect the old URL location. Since
Subversion 1.7 clients will go a step further,
automatically relocating the working copy to the new
URL.</p>
</td>
</tr>
</table>
</div>
<div class="sidebar" title="Switches and Updates">
<div class="titlepage">
<div>
<div>
<p class="title">
<strong>Switches and Updates</strong>
</p>
</div>
</div>
</div>
<p>Have you noticed that the output of <span class="command"><strong>svn
switch</strong></span> and <span class="command"><strong>svn update</strong></span> looks the
same? The switch command is actually a superset of the update
command.</p>
<p>When you run <span class="command"><strong>svn update</strong></span>, you're asking
the repository to compare two trees. The repository does so,
and then sends a description of the differences back to the
client. The only difference between <span class="command"><strong>svn
switch</strong></span> and <span class="command"><strong>svn update</strong></span> is that the
latter command always compares two identical repository
paths.</p>
<p>That is, if your working copy is a mirror of
<code class="filename">/calc/trunk</code>, <span class="command"><strong>svn
update</strong></span> will automatically compare your working copy
of <code class="filename">/calc/trunk</code> to
<code class="filename">/calc/trunk</code> in the
<code class="literal">HEAD</code> revision. If you're switching your
working copy to a branch, <span class="command"><strong>svn switch</strong></span>
will compare your working copy of
<code class="filename">/calc/trunk</code> to some
<span class="emphasis"><em>other</em></span> branch directory in the
<code class="literal">HEAD</code> revision.</p>
<p>In other words, an update moves your working copy through
time. A switch moves your working copy through time
<span class="emphasis"><em>and</em></span> space.</p>
</div>
<p>Because <span class="command"><strong>svn switch</strong></span> is essentially a
variant of <span class="command"><strong>svn update</strong></span>, it shares the same
behaviors; any local modifications in your working copy are
preserved when new data arrives from the repository.</p>
<div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Tip]" src="images/tip.png" />
</td>
<th align="left">Tip</th>
</tr>
<tr>
<td align="left" valign="top">
<p>Have you ever found yourself making some complex edits (in
your <code class="filename">/trunk</code> working copy) and suddenly
realized, <span class="quote">“<span class="quote">Hey, these changes ought to be in their own
branch?</span>”</span> There is a great two step technique to do
this:</p>
<div class="informalexample">
<pre class="screen">
$ svn copy http://svn.example.com/repos/calc/trunk \
http://svn.example.com/repos/calc/branches/newbranch \
-m "Create branch 'newbranch'."
Committed revision 353.
$ svn switch ^/calc/branches/newbranch
At revision 353.
</pre>
</div>
<p>The <span class="command"><strong>svn switch</strong></span> command, like
<span class="command"><strong>svn update</strong></span>, preserves your local edits. At
this point, your working copy is now a reflection of the newly
created branch, and your next <span class="command"><strong>svn commit</strong></span>
invocation will send your changes there.</p>
</td>
</tr>
</table>
</div>
<div class="footnotes">
<br />
<hr width="100" align="left" />
<div class="footnote">
<p><sup>[<a id="ftn.idp12808112" href="#idp12808112" class="para">43</a>] </sup>You <span class="emphasis"><em>can</em></span>, however,
use <span class="command"><strong>svn relocate</strong></span> if the URL of your server
changes and you don't want to abandon an existing working copy.
See <a class="xref" href="svn.ref.svn.c.relocate.html" title="svn relocate">svn relocate</a> in
<a class="xref" href="svn.ref.svn.html" title="svn Reference—Subversion Command-Line Client">svn Reference—Subversion Command-Line Client</a> for more information and an
example.</p>
</div>
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and C. Michael Pilato.</p>
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