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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 3. A tour of Mercurial: merging work</title><link rel="stylesheet" href="/support/styles.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.3"><link rel="home" href="index.html" title="Mercurial: The Definitive Guide"><link rel="up" href="index.html" title="Mercurial: The Definitive Guide"><link rel="prev" href="a-tour-of-mercurial-the-basics.html" title="Chapter 2. A tour of Mercurial: the basics"><link rel="next" href="behind-the-scenes.html" title="Chapter 4. Behind the scenes"><link rel="alternate" type="application/atom+xml" title="Comments" href="/feeds/comments/"><link rel="shortcut icon" type="image/png" href="/support/figs/favicon.png"><script type="text/javascript" src="/support/jquery-min.js"></script><script type="text/javascript" src="/support/form.js"></script><script type="text/javascript" src="/support/hsbook.js"></script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><h2 class="booktitle"><a href="/">Mercurial: The Definitive Guide</a><span class="authors">by Bryan O'Sullivan</span></h2></div><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. A tour of Mercurial: merging work</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="a-tour-of-mercurial-the-basics.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="behind-the-scenes.html">Next</a></td></tr></table></div><div class="chapter" lang="en" id="chap:tour-merge"><div class="titlepage"><div><div><h2 class="title">Chapter 3. A tour of Mercurial: merging work</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="a-tour-of-mercurial-merging-work.html#id352947">Merging streams of work</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-merging-work.html#id353683">Head changesets</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-merging-work.html#id353830">Performing the merge</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-merging-work.html#id353997">Committing the results of the merge</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-merging-work.html#id354262">Merging conflicting changes</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-merging-work.html#id354379">Using a graphical merge tool</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-merging-work.html#id354524">A worked example</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-merging-work.html#sec:tour-merge:fetch">Simplifying the pull-merge-commit sequence</a></span></dt><dt><span class="sect1"><a href="a-tour-of-mercurial-merging-work.html#id355904">Renaming, copying, and merging</a></span></dt></dl></div><p id="x_338"><a name="x_338"></a>We've now covered cloning a repository, making changes in a
repository, and pulling or pushing changes from one repository
into another. Our next step is <span class="emphasis"><em>merging</em></span>
changes from separate repositories.</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id352947">Merging streams of work</h2></div></div></div><p id="x_339"><a name="x_339"></a>Merging is a fundamental part of working with a distributed
revision control tool. Here are a few cases in which the need
to merge work arises.</p><div class="itemizedlist"><ul type="disc"><li><p id="x_33a"><a name="x_33a"></a>Alice and Bob each have a personal copy of a
repository for a project they're collaborating on. Alice
fixes a bug in her repository; Bob adds a new feature in
his. They want the shared repository to contain both the
bug fix and the new feature.</p></li><li><p id="x_33b"><a name="x_33b"></a>Cynthia frequently works on several different
tasks for a single project at once, each safely isolated in
its own repository. Working this way means that she often
needs to merge one piece of her own work with
another.</p></li></ul></div><p id="x_33c"><a name="x_33c"></a>Because we need to merge often, Mercurial makes
the process easy. Let's walk through a merge. We'll begin by
cloning yet another repository (see how often they spring up?)
and making a change in it.</p><pre id="id353643" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd ..</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg clone hello my-new-hello</code></strong>
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
<code class="prompt">$</code> <strong class="userinput"><code>cd my-new-hello</code></strong>
# Make some simple edits to hello.c.
<code class="prompt">$</code> <strong class="userinput"><code>my-text-editor hello.c</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg commit -m 'A new hello for a new day.'</code></strong>
</pre><p id="x_33d"><a name="x_33d"></a>We should now have two copies of
<code class="filename">hello.c</code> with different contents. The
histories of the two repositories have also diverged, as
illustrated in <a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:sep-repos" title="Figure 3.1. Divergent recent histories of the my-hello and my-new-hello repositories">Figure 3.1, “Divergent recent histories of the my-hello and my-new-hello
repositories”</a>. Here is a copy of our
file from one repository.</p><pre id="id353616" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cat hello.c</code></strong>
/*
* Placed in the public domain by Bryan O'Sullivan. This program is
* not covered by patents in the United States or other countries.
*/
#include &lt;stdio.h&gt;
int main(int argc, char **argv)
{
printf("once more, hello.\n");
printf("hello, world!\");
printf("hello again!\n");
return 0;
}
</pre><p id="x_722"><a name="x_722"></a>And here is our slightly different version from the other
repository.</p><pre id="id353585" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cat ../my-hello/hello.c</code></strong>
/*
* Placed in the public domain by Bryan O'Sullivan. This program is
* not covered by patents in the United States or other countries.
*/
#include &lt;stdio.h&gt;
int main(int argc, char **argv)
{
printf("hello, world!\");
printf("hello again!\n");
return 0;
}
</pre><div class="figure"><a name="fig:tour-merge:sep-repos"></a><p class="title"><b>Figure 3.1. Divergent recent histories of the <code class="filename">my-hello</code> and <code class="filename">my-new-hello</code>
repositories</b></p><div class="figure-contents"><div class="mediaobject"><img src="figs/tour-merge-sep-repos.png" alt="XXX add text"></div></div></div><br class="figure-break"><p id="x_33f"><a name="x_33f"></a>We already know that pulling changes from our <code class="filename">my-hello</code> repository will have no
effect on the working directory.</p><pre id="id353533" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg pull ../my-hello</code></strong>
pulling from ../my-hello
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
</pre><p id="x_340"><a name="x_340"></a>However, the <span class="command"><strong>hg pull</strong></span>
command says something about “<span class="quote">heads</span>”.</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id353683">Head changesets</h3></div></div></div><p id="x_341"><a name="x_341"></a>Remember that Mercurial records what the parent
of each change is. If a change has a parent, we call it a
child or descendant of the parent. A head is a change that
has no children. The tip revision is thus a head, because the
newest revision in a repository doesn't have any children.
There are times when a repository can contain more than one
head.</p><div class="figure"><a name="fig:tour-merge:pull"></a><p class="title"><b>Figure 3.2. Repository contents after pulling from <code class="filename">my-hello</code> into <code class="filename">my-new-hello</code></b></p><div class="figure-contents"><div class="mediaobject"><img src="figs/tour-merge-pull.png" alt="XXX add text"></div></div></div><br class="figure-break"><p id="x_343"><a name="x_343"></a>In <a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:pull" title="Figure 3.2. Repository contents after pulling from my-hello into my-new-hello">Figure 3.2, “Repository contents after pulling from my-hello into my-new-hello”</a>, you can
see the effect of the pull from <code class="filename">my-hello</code> into <code class="filename">my-new-hello</code>. The history that
was already present in <code class="filename">my-new-hello</code> is untouched, but
a new revision has been added. By referring to <a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:sep-repos" title="Figure 3.1. Divergent recent histories of the my-hello and my-new-hello repositories">Figure 3.1, “Divergent recent histories of the my-hello and my-new-hello
repositories”</a>, we can see that the
<span class="emphasis"><em>changeset ID</em></span> remains the same in the new
repository, but the <span class="emphasis"><em>revision number</em></span> has
changed. (This, incidentally, is a fine example of why it's
not safe to use revision numbers when discussing changesets.)
We can view the heads in a repository using the <span class="command"><strong>hg heads</strong></span> command.</p><pre id="id354126" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg heads</code></strong>
changeset: 6:b6fed4f21233
tag: tip
parent: 4:2278160e78d4
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:53 2009 +0000
summary: Added an extra line of output
changeset: 5:5218ee8aecf3
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:55 2009 +0000
summary: A new hello for a new day.
</pre></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id353830">Performing the merge</h3></div></div></div><p id="x_344"><a name="x_344"></a>What happens if we try to use the normal <span class="command"><strong>hg update</strong></span> command to update to the
new tip?</p><pre id="id354203" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg update</code></strong>
abort: crosses branches (use 'hg merge' or 'hg update -C')
</pre><p id="x_345"><a name="x_345"></a>Mercurial is telling us that the <span class="command"><strong>hg update</strong></span> command won't do a merge;
it won't update the working directory when it thinks we might
want to do a merge, unless we force it to do so.
(Incidentally, forcing the update with <span class="command"><strong>hg update
-C</strong></span> would revert any uncommitted changes in the
working directory.)</p><p id="x_723"><a name="x_723"></a>To start a merge between the two heads, we use the
<span class="command"><strong>hg merge</strong></span> command.</p><pre id="id354163" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg merge</code></strong>
merging hello.c
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
</pre><p id="x_347"><a name="x_347"></a>We resolve the contents of <code class="filename">hello.c</code>
This updates the working directory so that it
contains changes from <span class="emphasis"><em>both</em></span> heads, which
is reflected in both the output of <span class="command"><strong>hg
parents</strong></span> and the contents of
<code class="filename">hello.c</code>.</p><pre id="id354360" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg parents</code></strong>
changeset: 5:5218ee8aecf3
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:55 2009 +0000
summary: A new hello for a new day.
changeset: 6:b6fed4f21233
tag: tip
parent: 4:2278160e78d4
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:53 2009 +0000
summary: Added an extra line of output
<code class="prompt">$</code> <strong class="userinput"><code>cat hello.c</code></strong>
/*
* Placed in the public domain by Bryan O'Sullivan. This program is
* not covered by patents in the United States or other countries.
*/
#include &lt;stdio.h&gt;
int main(int argc, char **argv)
{
printf("once more, hello.\n");
printf("hello, world!\");
printf("hello again!\n");
return 0;
}
</pre></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id353997">Committing the results of the merge</h3></div></div></div><p id="x_348"><a name="x_348"></a>Whenever we've done a merge, <span class="command"><strong>hg
parents</strong></span> will display two parents until we <span class="command"><strong>hg commit</strong></span> the results of the
merge.</p><pre id="id354037" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg commit -m 'Merged changes'</code></strong>
</pre><p id="x_349"><a name="x_349"></a>We now have a new tip revision; notice that it has
<span class="emphasis"><em>both</em></span> of our former heads as its parents.
These are the same revisions that were previously displayed by
<span class="command"><strong>hg parents</strong></span>.</p><pre id="id354110" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg tip</code></strong>
changeset: 7:ecb0e17b2a4e
tag: tip
parent: 5:5218ee8aecf3
parent: 6:b6fed4f21233
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:56 2009 +0000
summary: Merged changes
</pre><p id="x_34a"><a name="x_34a"></a>In <a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:merge" title="Figure 3.3. Working directory and repository during merge, and following commit">Figure 3.3, “Working directory and repository during merge, and
following commit”</a>, you can see a
representation of what happens to the working directory during
the merge, and how this affects the repository when the commit
happens. During the merge, the working directory has two
parent changesets, and these become the parents of the new
changeset.</p><div class="figure"><a name="fig:tour-merge:merge"></a><p class="title"><b>Figure 3.3. Working directory and repository during merge, and
following commit</b></p><div class="figure-contents"><div class="mediaobject"><img src="figs/tour-merge-merge.png" alt="XXX add text"></div></div></div><br class="figure-break"><p id="x_69c"><a name="x_69c"></a>We sometimes talk about a merge having
<span class="emphasis"><em>sides</em></span>: the left side is the first parent
in the output of <span class="command"><strong>hg parents</strong></span>,
and the right side is the second. If the working directory
was at e.g. revision 5 before we began a merge, that revision
will become the left side of the merge.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id354262">Merging conflicting changes</h2></div></div></div><p id="x_34b"><a name="x_34b"></a>Most merges are simple affairs, but sometimes you'll find
yourself merging changes where each side modifies the same portions
of the same files. Unless both modifications are identical,
this results in a <span class="emphasis"><em>conflict</em></span>, where you have
to decide how to reconcile the different changes into something
coherent.</p><div class="figure"><a name="fig:tour-merge:conflict"></a><p class="title"><b>Figure 3.4. Conflicting changes to a document</b></p><div class="figure-contents"><div class="mediaobject"><img src="figs/tour-merge-conflict.png" alt="XXX add text"></div></div></div><br class="figure-break"><p id="x_34d"><a name="x_34d"></a><a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:conflict" title="Figure 3.4. Conflicting changes to a document">Figure 3.4, “Conflicting changes to a document”</a> illustrates
an instance of two conflicting changes to a document. We
started with a single version of the file; then we made some
changes; while someone else made different changes to the same
text. Our task in resolving the conflicting changes is to
decide what the file should look like.</p><p id="x_34e"><a name="x_34e"></a>Mercurial doesn't have a built-in facility for handling
conflicts. Instead, it runs an external program, usually one
that displays some kind of graphical conflict resolution
interface. By default, Mercurial tries to find one of several
different merging tools that are likely to be installed on your
system. It first tries a few fully automatic merging tools; if
these don't succeed (because the resolution process requires
human guidance) or aren't present, it tries a few
different graphical merging tools.</p><p id="x_34f"><a name="x_34f"></a>It's also possible to get Mercurial to run a
specific program or script, by setting the
<code class="envar">HGMERGE</code> environment variable to the name of your
preferred program.</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id354379">Using a graphical merge tool</h3></div></div></div><p id="x_350"><a name="x_350"></a>My preferred graphical merge tool is
<span class="command"><strong>kdiff3</strong></span>, which I'll use to describe the
features that are common to graphical file merging tools. You
can see a screenshot of <span class="command"><strong>kdiff3</strong></span> in action in
<a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:kdiff3" title="Figure 3.5. Using kdiff3 to merge versions of a file">Figure 3.5, “Using kdiff3 to merge versions of a
file”</a>. The kind of
merge it is performing is called a <span class="emphasis"><em>three-way
merge</em></span>, because there are three different versions
of the file of interest to us. The tool thus splits the upper
portion of the window into three panes:</p><div class="itemizedlist"><ul type="disc"><li><p id="x_351"><a name="x_351"></a>At the left is the <span class="emphasis"><em>base</em></span>
version of the file, i.e. the most recent version from
which the two versions we're trying to merge are
descended.</p></li><li><p id="x_352"><a name="x_352"></a>In the middle is “<span class="quote">our</span>” version of
the file, with the contents that we modified.</p></li><li><p id="x_353"><a name="x_353"></a>On the right is “<span class="quote">their</span>” version
of the file, the one that from the changeset that we're
trying to merge with.</p></li></ul></div><p id="x_354"><a name="x_354"></a>In the pane below these is the current
<span class="emphasis"><em>result</em></span> of the merge. Our task is to
replace all of the red text, which indicates unresolved
conflicts, with some sensible merger of the
<span class="quote">ours</span>” and “<span class="quote">theirs</span>” versions of the
file.</p><p id="x_355"><a name="x_355"></a>All four of these panes are <span class="emphasis"><em>locked
together</em></span>; if we scroll vertically or horizontally
in any of them, the others are updated to display the
corresponding sections of their respective files.</p><div class="figure"><a name="fig:tour-merge:kdiff3"></a><p class="title"><b>Figure 3.5. Using <span class="command">kdiff3</span> to merge versions of a
file</b></p><div class="figure-contents"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="100%"><tr><td><img src="figs/kdiff3.png" width="100%" alt="XXX add text"></td></tr></table></div></div></div><br class="figure-break"><p id="x_357"><a name="x_357"></a>For each conflicting portion of the file, we can choose to
resolve the conflict using some combination of text from the
base version, ours, or theirs. We can also manually edit the
merged file at any time, in case we need to make further
modifications.</p><p id="x_358"><a name="x_358"></a>There are <span class="emphasis"><em>many</em></span> file merging tools
available, too many to cover here. They vary in which
platforms they are available for, and in their particular
strengths and weaknesses. Most are tuned for merging files
containing plain text, while a few are aimed at specialised
file formats (generally XML).</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id354524">A worked example</h3></div></div></div><p id="x_359"><a name="x_359"></a>In this example, we will reproduce the file modification
history of <a class="xref" href="a-tour-of-mercurial-merging-work.html#fig:tour-merge:conflict" title="Figure 3.4. Conflicting changes to a document">Figure 3.4, “Conflicting changes to a document”</a>
above. Let's begin by creating a repository with a base
version of our document.</p><pre id="id354880" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cat &gt; letter.txt &lt;&lt;EOF</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Greetings!</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>I am Mariam Abacha, the wife of former</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Nigerian dictator Sani Abacha.</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>EOF</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg add letter.txt</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg commit -m '419 scam, first draft'</code></strong>
</pre><p id="x_35a"><a name="x_35a"></a>We'll clone the repository and make a change to the
file.</p><pre id="id354860" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd ..</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg clone scam scam-cousin</code></strong>
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
<code class="prompt">$</code> <strong class="userinput"><code>cd scam-cousin</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>cat &gt; letter.txt &lt;&lt;EOF</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Greetings!</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>I am Shehu Musa Abacha, cousin to the former</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Nigerian dictator Sani Abacha.</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>EOF</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg commit -m '419 scam, with cousin'</code></strong>
</pre><p id="x_35b"><a name="x_35b"></a>And another clone, to simulate someone else making a
change to the file. (This hints at the idea that it's not all
that unusual to merge with yourself when you isolate tasks in
separate repositories, and indeed to find and resolve
conflicts while doing so.)</p><pre id="id354843" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd ..</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg clone scam scam-son</code></strong>
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
<code class="prompt">$</code> <strong class="userinput"><code>cd scam-son</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>cat &gt; letter.txt &lt;&lt;EOF</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Greetings!</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>I am Alhaji Abba Abacha, son of the former</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Nigerian dictator Sani Abacha.</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>EOF</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg commit -m '419 scam, with son'</code></strong>
</pre><p id="x_35c"><a name="x_35c"></a>Having created two
different versions of the file, we'll set up an environment
suitable for running our merge.</p><pre id="id355540" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd ..</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg clone scam-cousin scam-merge</code></strong>
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
<code class="prompt">$</code> <strong class="userinput"><code>cd scam-merge</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg pull -u ../scam-son</code></strong>
pulling from ../scam-son
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
not updating, since new heads added
(run 'hg heads' to see heads, 'hg merge' to merge)
</pre><p id="x_35d"><a name="x_35d"></a>In this example, I'll set
<code class="envar">HGMERGE</code> to tell Mercurial to use the
non-interactive <span class="command"><strong>merge</strong></span> command. This is
bundled with many Unix-like systems. (If you're following this
example on your computer, don't bother setting
<code class="envar">HGMERGE</code>. You'll get dropped into a GUI file
merge tool instead, which is much preferable.)</p><pre id="id355530" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>export HGMERGE=merge</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg merge</code></strong>
merging letter.txt
merge: warning: conflicts during merge
merging letter.txt failed!
0 files updated, 0 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges or 'hg up --clean' to abandon
<code class="prompt">$</code> <strong class="userinput"><code>cat letter.txt</code></strong>
Greetings!
&lt;&lt;&lt;&lt;&lt;&lt;&lt; /tmp/tour-merge-conflictgW7-1Z/scam-merge/letter.txt
I am Shehu Musa Abacha, cousin to the former
=======
I am Alhaji Abba Abacha, son of the former
&gt;&gt;&gt;&gt;&gt;&gt;&gt; /tmp/letter.txt~other.c6Rq0s
Nigerian dictator Sani Abacha.
</pre><p id="x_35f"><a name="x_35f"></a>Because <span class="command"><strong>merge</strong></span> can't resolve the
conflicting changes, it leaves <span class="emphasis"><em>merge
markers</em></span> inside the file that has conflicts,
indicating which lines have conflicts, and whether they came
from our version of the file or theirs.</p><p id="x_360"><a name="x_360"></a>Mercurial can tell from the way <span class="command"><strong>merge</strong></span>
exits that it wasn't able to merge successfully, so it tells
us what commands we'll need to run if we want to redo the
merging operation. This could be useful if, for example, we
were running a graphical merge tool and quit because we were
confused or realised we had made a mistake.</p><p id="x_361"><a name="x_361"></a>If automatic or manual merges fail, there's nothing to
prevent us from “<span class="quote">fixing up</span>” the affected files
ourselves, and committing the results of our merge:</p><pre id="id355496" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cat &gt; letter.txt &lt;&lt;EOF</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Greetings!</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>I am Bryan O'Sullivan, no relation of the former</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>Nigerian dictator Sani Abacha.</code></strong>
<code class="prompt">&gt;</code> <strong class="userinput"><code>EOF</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg resolve -m letter.txt</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg commit -m 'Send me your money'</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg tip</code></strong>
changeset: 3:6f17ad930bf5
tag: tip
parent: 1:cef8fbca9a6f
parent: 2:dc8f64391590
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Tue May 05 06:55:57 2009 +0000
summary: Send me your money
</pre><div class="note"><table border="0" summary="Note: Where is the hg resolve command?"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="/support/figs/note.png"></td><th align="left">Where is the hg resolve command?</th></tr><tr><td align="left" valign="top"><p id="x_724"><a name="x_724"></a>The <span class="command"><strong>hg resolve</strong></span> command was introduced
in Mercurial 1.1, which was released in December 2008. If
you are using an older version of Mercurial (run <span class="command"><strong>hg
version</strong></span> to see), this command will not be
present. If your version of Mercurial is older than 1.1,
you should strongly consider upgrading to a newer version
before trying to tackle complicated merges.</p></td></tr></table></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="sec:tour-merge:fetch">Simplifying the pull-merge-commit sequence</h2></div></div></div><p id="x_362"><a name="x_362"></a>The process of merging changes as outlined above is
straightforward, but requires running three commands in
sequence.</p><pre id="id355698" class="programlisting">hg pull -u
hg merge
hg commit -m 'Merged remote changes'</pre><p id="x_363"><a name="x_363"></a>In the case of the final commit, you also need to enter a
commit message, which is almost always going to be a piece of
uninteresting “<span class="quote">boilerplate</span>” text.</p><p id="x_364"><a name="x_364"></a>It would be nice to reduce the number of steps needed, if
this were possible. Indeed, Mercurial is distributed with an
extension called <code class="literal">fetch</code> that
does just this.</p><p id="x_365"><a name="x_365"></a>Mercurial provides a flexible extension mechanism that lets
people extend its functionality, while keeping the core of
Mercurial small and easy to deal with. Some extensions add new
commands that you can use from the command line, while others
work “<span class="quote">behind the scenes,</span>” for example adding
capabilities to Mercurial's built-in server mode.</p><p id="x_366"><a name="x_366"></a>The <code class="literal">fetch</code>
extension adds a new command called, not surprisingly, <span class="command"><strong>hg fetch</strong></span>. This extension acts as a
combination of <span class="command"><strong>hg pull -u</strong></span>,
<span class="command"><strong>hg merge</strong></span> and <span class="command"><strong>hg commit</strong></span>. It begins by pulling
changes from another repository into the current repository. If
it finds that the changes added a new head to the repository, it
updates to the new head, begins a merge, then (if the merge
succeeded) commits the result of the merge with an
automatically-generated commit message. If no new heads were
added, it updates the working directory to the new tip
changeset.</p><p id="x_367"><a name="x_367"></a>Enabling the <code class="literal">fetch</code> extension is easy. Edit the
<code class="filename">.hgrc</code> file in your home
directory, and either go to the <code class="literal">extensions</code> section or create an
<code class="literal">extensions</code> section. Then
add a line that simply reads
<span class="quote"><code class="literal">fetch=</code></span>”.</p><pre id="id355838" class="programlisting">[extensions]
fetch =</pre><p id="x_368"><a name="x_368"></a>(Normally, the right-hand side of the
<span class="quote"><code class="literal">=</code></span>” would indicate where to find
the extension, but since the <code class="literal">fetch</code> extension is in the standard
distribution, Mercurial knows where to search for it.)</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id355904">Renaming, copying, and merging</h2></div></div></div><p id="x_729"><a name="x_729"></a>During the life of a project, we will often want to change
the layout of its files and directories. This can be as simple
as renaming a single file, or as complex as restructuring the
entire hierarchy of files within the project.</p><p id="x_72a"><a name="x_72a"></a>Mercurial supports these kinds of complex changes fluently,
provided we tell it what we're doing. If we want to rename a
file, we should use the <span class="command"><strong>hg rename</strong></span><sup>[<a name="id355926" href="#ftn.id355926" class="footnote">2</a>]</sup> command to rename it, so that Mercurial can do the
right thing later when we merge.</p><p id="x_72c"><a name="x_72c"></a>We will cover the use of these commands in more detail in
<a class="xref" href="mercurial-in-daily-use.html#chap:daily.copy" title="Copying files">the section called “Copying files”</a>.</p></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"><p><sup>[<a name="ftn.id355926" href="#id355926" class="para">2</a>] </sup>If you're a Unix user, you'll be glad to know that the
<span class="command"><strong>hg rename</strong></span> command can be abbreviated as
<span class="command"><strong>hg mv</strong></span>.</p></div></div></div><div class="hgfooter"><p><img src="/support/figs/rss.png"> Want to stay up to date? Subscribe to the comment feed for <a id="chapterfeed" class="feed" href="/feeds/comments/">this chapter</a>, or the <a class="feed" href="/feeds/comments/">entire book</a>.</p><p>Copyright 2006, 2007, 2008, 2009 Bryan O'Sullivan.
Icons by <a href="mailto:mattahan@gmail.com">Paul Davey</a> aka <a href="http://mattahan.deviantart.com/">Mattahan</a>.</p></div><div class="navfooter"><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="a-tour-of-mercurial-the-basics.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="behind-the-scenes.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 2. A tour of Mercurial: the basics </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 4. Behind the scenes</td></tr></table></div><script type="text/javascript">
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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 2. A tour of Mercurial: the basics</title><link rel="stylesheet" href="/support/styles.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.3"><link rel="home" href="index.html" title="Mercurial: The Definitive Guide"><link rel="up" href="index.html" title="Mercurial: The Definitive Guide"><link rel="prev" href="how-did-we-get-here.html" title="Chapter 1. How did we get here?"><link rel="next" href="a-tour-of-mercurial-merging-work.html" title="Chapter 3. A tour of Mercurial: merging work"><link rel="alternate" type="application/atom+xml" title="Comments" href="/feeds/comments/"><link rel="shortcut icon" type="image/png" href="/support/figs/favicon.png"><script type="text/javascript" src="/support/jquery-min.js"></script><script type="text/javascript" src="/support/form.js"></script><script type="text/javascript" src="/support/hsbook.js"></script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><h2 class="booktitle"><a href="/">Mercurial: The Definitive Guide</a><span class="authors">by Bryan O'Sullivan</span></h2></div><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 2. A tour of Mercurial: the basics</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="how-did-we-get-here.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="a-tour-of-mercurial-merging-work.html">Next</a></td></tr></table></div><div class="chapter" lang="en" id="chap:tour-basic"><div class="titlepage"><div><div><h2 class="title">Chapter 2. A tour of Mercurial: the basics</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#sec:tour:install">Installing Mercurial on your system</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id344575">Windows</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id344904">Mac OS X</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id344922">Linux</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id344998">Solaris</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id345016">Getting started</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id345318">Built-in help</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id345120">Working with a repository</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id345147">Making a local copy of a repository</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id345415">What's in a repository?</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id345536">A tour through history</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id345833">Changesets, revisions, and talking to other
people</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id345980">Viewing specific revisions</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id346082">More detailed information</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id346408">All about command options</a></span></dt><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id346595">Making and reviewing changes</a></span></dt><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id347157">Recording changes in a new changeset</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id347208">Setting up a username</a></span></dt><dd><dl><dt><span class="sect3"><a href="a-tour-of-mercurial-the-basics.html#sec:tour-basic:username">Creating a Mercurial configuration file</a></span></dt><dt><span class="sect3"><a href="a-tour-of-mercurial-the-basics.html#id347496">Choosing a user name</a></span></dt></dl></dd><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id347526">Writing a commit message</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id347874">Writing a good commit message</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id347674">Aborting a commit</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id347689">Admiring our new handiwork</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id347917">Sharing changes</a></span></dt><dd><dl><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#sec:tour:pull">Pulling changes from another repository</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id348343">Updating the working directory</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id348825">Pushing changes to another repository</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id349161">Default locations</a></span></dt><dt><span class="sect2"><a href="a-tour-of-mercurial-the-basics.html#id349277">Sharing changes over a network</a></span></dt></dl></dd><dt><span class="sect1"><a href="a-tour-of-mercurial-the-basics.html#id349357">Starting a new project</a></span></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="sec:tour:install">Installing Mercurial on your system</h2></div></div></div><p id="x_1"><a name="x_1"></a>Prebuilt binary packages of Mercurial are available for
every popular operating system. These make it easy to start
using Mercurial on your computer immediately.</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id344575">Windows</h3></div></div></div><p id="x_c"><a name="x_c"></a>The best version of Mercurial for Windows is
TortoiseHg, which can be found at <a class="ulink" href="http://bitbucket.org/tortoisehg/stable/wiki/Home" target="_top">http://bitbucket.org/tortoisehg/stable/wiki/Home</a>.
This package has no external dependencies; it “<span class="quote">just
works</span>”. It provides both command line and graphical
user interfaces.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id344904">Mac OS X</h3></div></div></div><p id="x_a"><a name="x_a"></a>Lee Cantey publishes an installer of Mercurial
for Mac OS X at <a class="ulink" href="http://mercurial.berkwood.com" target="_top">http://mercurial.berkwood.com</a>.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id344922">Linux</h3></div></div></div><p id="x_2"><a name="x_2"></a>Because each Linux distribution has its own packaging
tools, policies, and rate of development, it's difficult to
give a comprehensive set of instructions on how to install
Mercurial binaries. The version of Mercurial that you will
end up with can vary depending on how active the person is who
maintains the package for your distribution.</p><p id="x_3"><a name="x_3"></a>To keep things simple, I will focus on installing
Mercurial from the command line under the most popular Linux
distributions. Most of these distributions provide graphical
package managers that will let you install Mercurial with a
single click; the package name to look for is
<code class="literal">mercurial</code>.</p><div class="itemizedlist"><ul type="disc"><li><p id="x_4"><a name="x_4"></a>Ubuntu and Debian:</p><pre id="id344957" class="programlisting">apt-get install mercurial</pre></li><li><p id="x_5"><a name="x_5"></a>Fedora:</p><pre id="id344968" class="programlisting">yum install mercurial</pre></li><li><p id="x_715"><a name="x_715"></a>OpenSUSE:</p><pre id="id344980" class="programlisting">zypper install mercurial</pre></li><li><p id="x_6"><a name="x_6"></a>Gentoo:</p><pre id="id344991" class="programlisting">emerge mercurial</pre></li></ul></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id344998">Solaris</h3></div></div></div><p id="x_9"><a name="x_9"></a>SunFreeWare, at <a class="ulink" href="http://www.sunfreeware.com" target="_top">http://www.sunfreeware.com</a>,
provides prebuilt packages of Mercurial.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id345016">Getting started</h2></div></div></div><p id="x_e"><a name="x_e"></a>To begin, we'll use the <span class="command"><strong>hg
version</strong></span> command to find out whether Mercurial is
installed properly. The actual version information that it
prints isn't so important; we simply care whether the command
runs and prints anything at all.</p><pre id="id345379" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg version</code></strong>
Mercurial Distributed SCM (version 1.2)
Copyright (C) 2005-2008 Matt Mackall &lt;mpm@selenic.com&gt; and others
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
</pre><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id345318">Built-in help</h3></div></div></div><p id="x_f"><a name="x_f"></a>Mercurial provides a built-in help system. This is
invaluable for those times when you find yourself stuck
trying to remember how to run a command. If you are
completely stuck, simply run <span class="command"><strong>hg
help</strong></span>; it will print a brief list of commands,
along with a description of what each does. If you ask for
help on a specific command (as below), it prints more
detailed information.</p><pre id="id345368" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg help init</code></strong>
hg init [-e CMD] [--remotecmd CMD] [DEST]
create a new repository in the given directory
Initialize a new repository in the given directory. If the given
directory does not exist, it is created.
If no directory is given, the current directory is used.
It is possible to specify an ssh:// URL as the destination.
See 'hg help urls' for more information.
options:
-e --ssh specify ssh command to use
--remotecmd specify hg command to run on the remote side
use "hg -v help init" to show global options
</pre><p id="x_10"><a name="x_10"></a>For a more impressive level of detail (which you won't
usually need) run <span class="command"><strong>hg help <code class="option">-v</code></strong></span>. The <code class="option">-v</code> option is short for
<code class="option">--verbose</code>, and tells
Mercurial to print more information than it usually
would.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id345120">Working with a repository</h2></div></div></div><p id="x_11"><a name="x_11"></a>In Mercurial, everything happens inside a
<span class="emphasis"><em>repository</em></span>. The repository for a project
contains all of the files that “<span class="quote">belong to</span>” that
project, along with a historical record of the project's
files.</p><p id="x_12"><a name="x_12"></a>There's nothing particularly magical about a repository; it
is simply a directory tree in your filesystem that Mercurial
treats as special. You can rename or delete a repository any
time you like, using either the command line or your file
browser.</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id345147">Making a local copy of a repository</h3></div></div></div><p id="x_13"><a name="x_13"></a><span class="emphasis"><em>Copying</em></span> a repository is just a little
bit special. While you could use a normal file copying
command to make a copy of a repository, it's best to use a
built-in command that Mercurial provides. This command is
called <span class="command"><strong>hg clone</strong></span>, because it
makes an identical copy of an existing repository.</p><pre id="id345593" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg clone https://bitbucket.org/bos/hg-tutorial-hello</code></strong>
destination directory: hello
requesting all changes
adding changesets
adding manifests
adding file changes
added 5 changesets with 5 changes to 2 files
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
</pre><p id="x_67c"><a name="x_67c"></a>One advantage of using <span class="command"><strong>hg
clone</strong></span> is that, as we can see above, it lets us clone
repositories over the network. Another is that it remembers
where we cloned from, which we'll find useful soon when we
want to fetch new changes from another repository.</p><p id="x_14"><a name="x_14"></a>If our clone succeeded, we should now have a local
directory called <code class="filename">hello</code>.
This directory will contain some files.</p><pre id="id345299" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>ls -l</code></strong>
total 4
drwxrwxr-x 3 bos bos 4096 May 5 06:55 hello
<code class="prompt">$</code> <strong class="userinput"><code>ls hello</code></strong>
Makefile hello.c
</pre><p id="x_15"><a name="x_15"></a>These files have the same contents and history in our
repository as they do in the repository we cloned.</p><p id="x_16"><a name="x_16"></a>Every Mercurial repository is complete,
self-contained, and independent. It contains its own private
copy of a project's files and history. As we just mentioned,
a cloned repository remembers the location of the repository
it was cloned from, but Mercurial will not communicate with
that repository, or any other, unless you tell it to.</p><p id="x_17"><a name="x_17"></a>What this means for now is that we're free to experiment
with our repository, safe in the knowledge that it's a private
<span class="quote">sandbox</span>” that won't affect anyone else.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id345415">What's in a repository?</h3></div></div></div><p id="x_18"><a name="x_18"></a>When we take a more detailed look inside a repository, we
can see that it contains a directory named <code class="filename">.hg</code>. This is where Mercurial
keeps all of its metadata for the repository.</p><pre id="id345568" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd hello</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>ls -a</code></strong>
. .. .hg Makefile hello.c
</pre><p id="x_19"><a name="x_19"></a>The contents of the <code class="filename">.hg</code> directory and its
subdirectories are private to Mercurial. Every other file and
directory in the repository is yours to do with as you
please.</p><p id="x_1a"><a name="x_1a"></a>To introduce a little terminology, the <code class="filename">.hg</code> directory is the
<span class="quote">real</span>” repository, and all of the files and
directories that coexist with it are said to live in the
<span class="emphasis"><em>working directory</em></span>. An easy way to
remember the distinction is that the
<span class="emphasis"><em>repository</em></span> contains the
<span class="emphasis"><em>history</em></span> of your project, while the
<span class="emphasis"><em>working directory</em></span> contains a
<span class="emphasis"><em>snapshot</em></span> of your project at a particular
point in history.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id345536">A tour through history</h2></div></div></div><p id="x_1b"><a name="x_1b"></a>One of the first things we might want to do with a new,
unfamiliar repository is understand its history. The <span class="command"><strong>hg log</strong></span> command gives us a view of
the history of changes in the repository.</p><pre id="id345930" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg log</code></strong>
changeset: 4:2278160e78d4
tag: tip
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:16:53 2008 +0200
summary: Trim comments.
changeset: 3:0272e0d5a517
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:08:02 2008 +0200
summary: Get make to generate the final binary from a .o file.
changeset: 2:fef857204a0c
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:05:04 2008 +0200
summary: Introduce a typo into hello.c.
changeset: 1:82e55d328c8c
user: mpm@selenic.com
date: Fri Aug 26 01:21:28 2005 -0700
summary: Create a makefile
changeset: 0:0a04b987be5a
user: mpm@selenic.com
date: Fri Aug 26 01:20:50 2005 -0700
summary: Create a standard "hello, world" program
</pre><p id="x_1c"><a name="x_1c"></a>By default, this command prints a brief paragraph of output
for each change to the project that was recorded. In Mercurial
terminology, we call each of these recorded events a
<span class="emphasis"><em>changeset</em></span>, because it can contain a record
of changes to several files.</p><p id="x_1d"><a name="x_1d"></a>The fields in a record of output from <span class="command"><strong>hg log</strong></span> are as follows.</p><div class="itemizedlist"><ul type="disc"><li><p id="x_1e"><a name="x_1e"></a><code class="literal">changeset</code>: This
field has the format of a number, followed by a colon,
followed by a hexadecimal (or <span class="emphasis"><em>hex</em></span>)
string. These are <span class="emphasis"><em>identifiers</em></span> for the
changeset. The hex string is a unique identifier: the same
hex string will always refer to the same changeset in every
copy of this repository. The
number is shorter and easier to type than the hex string,
but it isn't unique: the same number in two different clones
of a repository may identify different changesets.</p></li><li><p id="x_1f"><a name="x_1f"></a><code class="literal">user</code>: The identity of the
person who created the changeset. This is a free-form
field, but it most often contains a person's name and email
address.</p></li><li><p id="x_20"><a name="x_20"></a><code class="literal">date</code>: The date and time on
which the changeset was created, and the timezone in which
it was created. (The date and time are local to that
timezone; they display what time and date it was for the
person who created the changeset.)</p></li><li><p id="x_21"><a name="x_21"></a><code class="literal">summary</code>: The first line of
the text message that the creator of the changeset entered
to describe the changeset.</p></li><li><p id="x_67d"><a name="x_67d"></a>Some changesets, such as the first in the list above,
have a <code class="literal">tag</code> field. A tag is another way
to identify a changeset, by giving it an easy-to-remember
name. (The tag named <code class="literal">tip</code> is special: it
always refers to the newest change in a repository.)</p></li></ul></div><p id="x_22"><a name="x_22"></a>The default output printed by <span class="command"><strong>hg log</strong></span> is purely a summary; it is
missing a lot of detail.</p><p id="x_23"><a name="x_23"></a><a class="xref" href="a-tour-of-mercurial-the-basics.html#fig:tour-basic:history" title="Figure 2.1. Graphical history of the hello repository">Figure 2.1, “Graphical history of the hello repository”</a> provides
a graphical representation of the history of the <code class="filename">hello</code> repository, to make it a
little easier to see which direction history is
<span class="quote">flowing</span>” in. We'll be returning to this figure
several times in this chapter and the chapter that
follows.</p><div class="figure"><a name="fig:tour-basic:history"></a><p class="title"><b>Figure 2.1. Graphical history of the <code class="filename">hello</code> repository</b></p><div class="figure-contents"><div class="mediaobject"><img src="figs/tour-history.png" alt="XXX add text"></div></div></div><br class="figure-break"><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id345833">Changesets, revisions, and talking to other
people</h3></div></div></div><p id="x_25"><a name="x_25"></a>As English is a notoriously sloppy language, and computer
science has a hallowed history of terminological confusion
(why use one term when four will do?), revision control has a
variety of words and phrases that mean the same thing. If you
are talking about Mercurial history with other people, you
will find that the word “<span class="quote">changeset</span>” is often
compressed to “<span class="quote">change</span>” or (when written)
<span class="quote">cset</span>”, and sometimes a changeset is referred to
as a “<span class="quote">revision</span>” or a “<span class="quote">rev</span>”.</p><p id="x_26"><a name="x_26"></a>While it doesn't matter what <span class="emphasis"><em>word</em></span> you
use to refer to the concept of “<span class="quote">a changeset</span>”, the
<span class="emphasis"><em>identifier</em></span> that you use to refer to
<span class="quote">a <span class="emphasis"><em>specific</em></span> changeset</span>” is of
great importance. Recall that the <code class="literal">changeset</code>
field in the output from <span class="command"><strong>hg
log</strong></span> identifies a changeset using both a number and
a hexadecimal string.</p><div class="itemizedlist"><ul type="disc"><li><p id="x_27"><a name="x_27"></a>The revision number is a handy
notation that is <span class="emphasis"><em>only valid in that
repository</em></span>.</p></li><li><p id="x_28"><a name="x_28"></a>The hexadecimal string is the
<span class="emphasis"><em>permanent, unchanging identifier</em></span> that
will always identify that exact changeset in
<span class="emphasis"><em>every</em></span> copy of the
repository.</p></li></ul></div><p id="x_29"><a name="x_29"></a>This distinction is important. If you send
someone an email talking about “<span class="quote">revision 33</span>”,
there's a high likelihood that their revision 33 will
<span class="emphasis"><em>not be the same</em></span> as yours. The reason for
this is that a revision number depends on the order in which
changes arrived in a repository, and there is no guarantee
that the same changes will happen in the same order in
different repositories. Three changes <code class="literal">a,b,c</code>
can easily appear in one repository as
<code class="literal">0,1,2</code>, while in another as
<code class="literal">0,2,1</code>.</p><p id="x_2a"><a name="x_2a"></a>Mercurial uses revision numbers purely as a convenient
shorthand. If you need to discuss a changeset with someone,
or make a record of a changeset for some other reason (for
example, in a bug report), use the hexadecimal
identifier.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id345980">Viewing specific revisions</h3></div></div></div><p id="x_2b"><a name="x_2b"></a>To narrow the output of <span class="command"><strong>hg
log</strong></span> down to a single revision, use the <code class="option">-r</code> (or <code class="option">--rev</code>) option. You can use
either a revision number or a hexadecimal identifier,
and you can provide as many revisions as you want.</p><pre id="id346352" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg log -r 3</code></strong>
changeset: 3:0272e0d5a517
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:08:02 2008 +0200
summary: Get make to generate the final binary from a .o file.
<code class="prompt">$</code> <strong class="userinput"><code>hg log -r 0272e0d5a517</code></strong>
changeset: 3:0272e0d5a517
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:08:02 2008 +0200
summary: Get make to generate the final binary from a .o file.
<code class="prompt">$</code> <strong class="userinput"><code>hg log -r 1 -r 4</code></strong>
changeset: 1:82e55d328c8c
user: mpm@selenic.com
date: Fri Aug 26 01:21:28 2005 -0700
summary: Create a makefile
changeset: 4:2278160e78d4
tag: tip
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:16:53 2008 +0200
summary: Trim comments.
</pre><p id="x_2c"><a name="x_2c"></a>If you want to see the history of several revisions
without having to list each one, you can use <span class="emphasis"><em>range
notation</em></span>; this lets you express the idea “<span class="quote">I
want all revisions between <code class="literal">abc</code> and
<code class="literal">def</code>, inclusive</span>”.</p><pre id="id346245" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg log -r 2:4</code></strong>
changeset: 2:fef857204a0c
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:05:04 2008 +0200
summary: Introduce a typo into hello.c.
changeset: 3:0272e0d5a517
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:08:02 2008 +0200
summary: Get make to generate the final binary from a .o file.
changeset: 4:2278160e78d4
tag: tip
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:16:53 2008 +0200
summary: Trim comments.
</pre><p id="x_2d"><a name="x_2d"></a>Mercurial also honours the order in which you specify
revisions, so <span class="command"><strong>hg log -r 2:4</strong></span>
prints 2, 3, and 4. while <span class="command"><strong>hg log -r
4:2</strong></span> prints 4, 3, and 2.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id346082">More detailed information</h3></div></div></div><p id="x_2e"><a name="x_2e"></a>While the summary information printed by <span class="command"><strong>hg log</strong></span> is useful if you already know
what you're looking for, you may need to see a complete
description of the change, or a list of the files changed, if
you're trying to decide whether a changeset is the one you're
looking for. The <span class="command"><strong>hg log</strong></span>
command's <code class="option">-v</code> (or <code class="option">--verbose</code>) option gives you
this extra detail.</p><pre id="id346186" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg log -v -r 3</code></strong>
changeset: 3:0272e0d5a517
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:08:02 2008 +0200
files: Makefile
description:
Get make to generate the final binary from a .o file.
</pre><p id="x_2f"><a name="x_2f"></a>If you want to see both the description and
content of a change, add the <code class="option">-p</code> (or <code class="option">--patch</code>) option. This displays
the content of a change as a <span class="emphasis"><em>unified diff</em></span>
(if you've never seen a unified diff before, see <a class="xref" href="managing-change-with-mercurial-queues.html#sec:mq:patch" title="Understanding patches">the section called “Understanding patches”</a> for an overview).</p><pre id="id346230" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg log -v -p -r 2</code></strong>
changeset: 2:fef857204a0c
user: Bryan O'Sullivan &lt;bos@serpentine.com&gt;
date: Sat Aug 16 22:05:04 2008 +0200
files: hello.c
description:
Introduce a typo into hello.c.
diff -r 82e55d328c8c -r fef857204a0c hello.c
--- a/hello.c Fri Aug 26 01:21:28 2005 -0700
+++ b/hello.c Sat Aug 16 22:05:04 2008 +0200
@@ -11,6 +11,6 @@
int main(int argc, char **argv)
{
- printf("hello, world!\n");
+ printf("hello, world!\");
return 0;
}
</pre><p id="x_67e"><a name="x_67e"></a>The <code class="option">-p</code> option is
tremendously useful, so it's well worth remembering.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id346408">All about command options</h2></div></div></div><p id="x_30"><a name="x_30"></a>Let's take a brief break from exploring Mercurial commands
to discuss a pattern in the way that they work; you may find
this useful to keep in mind as we continue our tour.</p><p id="x_31"><a name="x_31"></a>Mercurial has a consistent and straightforward approach to
dealing with the options that you can pass to commands. It
follows the conventions for options that are common to modern
Linux and Unix systems.</p><div class="itemizedlist"><ul type="disc"><li><p id="x_32"><a name="x_32"></a>Every option has a long name. For example, as
we've already seen, the <span class="command"><strong>hg
log</strong></span> command accepts a <code class="option">--rev</code> option.</p></li><li><p id="x_33"><a name="x_33"></a>Most options have short names, too. Instead
of <code class="option">--rev</code>, we can use
<code class="option">-r</code>. (The reason that
some options don't have short names is that the options in
question are rarely used.)</p></li><li><p id="x_34"><a name="x_34"></a>Long options start with two dashes (e.g.
<code class="option">--rev</code>), while short
options start with one (e.g. <code class="option">-r</code>).</p></li><li><p id="x_35"><a name="x_35"></a>Option naming and usage is consistent across
commands. For example, every command that lets you specify
a changeset ID or revision number accepts both <code class="option">-r</code> and <code class="option">--rev</code> arguments.</p></li><li><p id="x_67f"><a name="x_67f"></a>If you are using short options, you can save typing by
running them together. For example, the command <span class="command"><strong>hg log -v -p -r 2</strong></span> can be written
as <span class="command"><strong>hg log -vpr2</strong></span>.</p></li></ul></div><p id="x_36"><a name="x_36"></a>In the examples throughout this book, I usually
use short options instead of long. This simply reflects my own
preference, so don't read anything significant into it.</p><p id="x_37"><a name="x_37"></a>Most commands that print output of some kind will print more
output when passed a <code class="option">-v</code>
(or <code class="option">--verbose</code>) option, and
less when passed <code class="option">-q</code> (or
<code class="option">--quiet</code>).</p><div class="note"><table border="0" summary="Note: Option naming consistency"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="/support/figs/note.png"></td><th align="left">Option naming consistency</th></tr><tr><td align="left" valign="top"><p id="x_680"><a name="x_680"></a>Almost always, Mercurial commands use consistent option
names to refer to the same concepts. For instance, if a
command deals with changesets, you'll always identify them
with <code class="option">--rev</code> or <code class="option">-r</code>. This consistent use of
option names makes it easier to remember what options a
particular command takes.</p></td></tr></table></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id346595">Making and reviewing changes</h2></div></div></div><p id="x_38"><a name="x_38"></a>Now that we have a grasp of viewing history in Mercurial,
let's take a look at making some changes and examining
them.</p><p id="x_39"><a name="x_39"></a>The first thing we'll do is isolate our experiment in a
repository of its own. We use the <span class="command"><strong>hg
clone</strong></span> command, but we don't need to clone a copy of
the remote repository. Since we already have a copy of it
locally, we can just clone that instead. This is much faster
than cloning over the network, and cloning a local repository
uses less disk space in most cases, too<sup>[<a name="id346621" href="#ftn.id346621" class="footnote">1</a>]</sup>.</p><pre id="id344876" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cd ..</code></strong>
<code class="prompt">$</code> <strong class="userinput"><code>hg clone hello my-hello</code></strong>
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
<code class="prompt">$</code> <strong class="userinput"><code>cd my-hello</code></strong>
</pre><p id="x_3a"><a name="x_3a"></a>As an aside, it's often good practice to keep a
<span class="quote">pristine</span>” copy of a remote repository around,
which you can then make temporary clones of to create sandboxes
for each task you want to work on. This lets you work on
multiple tasks in parallel, each isolated from the others until
it's complete and you're ready to integrate it back. Because
local clones are so cheap, there's almost no overhead to cloning
and destroying repositories whenever you want.</p><p id="x_3b"><a name="x_3b"></a>In our <code class="filename">my-hello</code>
repository, we have a file <code class="filename">hello.c</code> that
contains the classic “<span class="quote">hello, world</span>” program.</p><pre id="id347024" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>cat hello.c</code></strong>
/*
* Placed in the public domain by Bryan O'Sullivan. This program is
* not covered by patents in the United States or other countries.
*/
#include &lt;stdio.h&gt;
int main(int argc, char **argv)
{
printf("hello, world!\");
return 0;
}
</pre><p id="x_682"><a name="x_682"></a>Let's edit this file so that it prints a second line of
output.</p><pre id="id346984" class="screen"># ... edit edit edit ...
<code class="prompt">$</code> <strong class="userinput"><code>cat hello.c</code></strong>
/*
* Placed in the public domain by Bryan O'Sullivan. This program is
* not covered by patents in the United States or other countries.
*/
#include &lt;stdio.h&gt;
int main(int argc, char **argv)
{
printf("hello, world!\");
printf("hello again!\n");
return 0;
}
</pre><p id="x_3c"><a name="x_3c"></a>Mercurial's <span class="command"><strong>hg status</strong></span>
command will tell us what Mercurial knows about the files in the
repository.</p><pre id="id346930" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>ls</code></strong>
Makefile hello.c
<code class="prompt">$</code> <strong class="userinput"><code>hg status</code></strong>
M hello.c
</pre><p id="x_3d"><a name="x_3d"></a>The <span class="command"><strong>hg status</strong></span> command
prints no output for some files, but a line starting with
<span class="quote"><code class="literal">M</code></span>” for
<code class="filename">hello.c</code>. Unless you tell it to, <span class="command"><strong>hg status</strong></span> will not print any output
for files that have not been modified.</p><p id="x_3e"><a name="x_3e"></a>The “<span class="quote"><code class="literal">M</code></span>” indicates that
Mercurial has noticed that we modified
<code class="filename">hello.c</code>. We didn't need to
<span class="emphasis"><em>inform</em></span> Mercurial that we were going to
modify the file before we started, or that we had modified the
file after we were done; it was able to figure this out
itself.</p><p id="x_3f"><a name="x_3f"></a>It's somewhat helpful to know that we've modified
<code class="filename">hello.c</code>, but we might prefer to know
exactly <span class="emphasis"><em>what</em></span> changes we've made to it. To
do this, we use the <span class="command"><strong>hg diff</strong></span>
command.</p><pre id="id347442" class="screen"><code class="prompt">$</code> <strong class="userinput"><code>hg diff</code></strong>
diff -r 2278160e78d4 hello.c
--- a/hello.c Sat Aug 16 22:16:53 2008 +0200
+++ b/hello.c Tue May 05 06:55:53 2009 +0000
@@ -8,5 +8,6 @@
int main(int argc, char **argv)
{
printf("hello, world!\");
+ printf("hello again!\n");
return 0;
}
</pre><div class="tip"><table border="0" summary="Tip: Understanding patches"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="/support/figs/tip.png"></td><th align="left">Understanding patches</th></tr><tr><td align="left" valign="top"><p id="x_683"><a name="x_683"></a>Remember to take a look at <a class="xref" href="managing-change-with-mercurial-queues.html#sec:mq:patch" title="Understanding patches">the section called “Understanding patches”</a> if you don't know how to read
output above.</p></td></tr></table></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both" id="id347157">Recording changes in a new changeset</h2></div></div></div><p id="x_40"><a name="x_40"></a>We can modify files, build and test our changes, and use
<span class="command"><strong>hg status</strong></span> and <span class="command"><strong>hg diff</strong></span> to review our changes, until
we're satisfied with what we've done and arrive at a natural
stopping point where we want to record our work in a new
changeset.</p><p id="x_41"><a name="x_41"></a>The <span class="command"><strong>hg commit</strong></span> command lets
us create a new changeset; we'll usually refer to this as
<span class="quote">making a commit</span>” or
<span class="quote">committing</span>”.</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title" id="id347208">Setting up a username</h3></div></div></div><p id="x_42"><a name="x_42"></a>When you try to run <span class="command"><strong>hg
commit</strong></span> for the first time, it is not guaranteed to
succeed. Mercurial records your name and address with each
change that you commit, so that you and others will later be
able to tell who made each change. Mercurial tries to
automatically figure out a sensible username to commit the
change with. It will attempt each of the following methods,
in order:</p><div class="orderedlist"><ol type="1"><li><p id="x_43"><a name="x_43"></a>If you specify a <code class="option">-u</code> option to the <span class="command"><strong>hg commit</strong></span> command on the command
line, followed by a username, this is always given the
highest precedence.</p></li><li><p id="x_44"><a name="x_44"></a>If you have set the <code class="envar">HGUSER</code>
environment variable, this is checked
next.</p></li><li><p id="x_45"><a name="x_45"></a>If you create a file in your home
directory called <code class="filename">.hgrc</code>, with a <code class="envar">username</code> entry, that will be
used next. To see what the contents of this file should
look like, refer to <a class="xref" href="a-tour-of-mercurial-the-basics.html#sec:tour-basic:username" title="Creating a Mercurial configuration file">the section called “Creating a Mercurial configuration file”</a>
below.</p></li><li><p id="x_46"><a name=