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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User Manual</title><link rel="stylesheet" type="text/css" href="docbook-xsl.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="id-1"></a>Git User Manual</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#_introduction">Introduction</a></span></dt><dt><span class="chapter"><a href="#repositories-and-branches">1. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#exploring-git-history">2. Exploring Git history</a></span></dt><dd><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#Developing-With-git">3. Developing with Git</a></span></dt><dd><dl><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#sharing-development">4. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">5. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#advanced-branch-management">6. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote-tracking branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#git-concepts">7. Git concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How Git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></dd><dt><span class="chapter"><a href="#submodules">8. Submodules</a></span></dt><dd><dl><dt><span class="section"><a href="#pitfalls-with-submodules">Pitfalls with submodules</a></span></dt></dl></dd><dt><span class="chapter"><a href="#low-level-operations">9. Low-level Git operations</a></span></dt><dd><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory → index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index → object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database → index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index → working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hacking-git">10. Hacking Git</a></span></dt><dd><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git’s source code</a></span></dt></dl></dd><dt><span class="chapter"><a href="#glossary">11. Git Glossary</a></span></dt><dd><dl><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></dd><dt><span class="appendix"><a href="#git-quick-start">A. Git Quick Reference</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></dd><dt><span class="appendix"><a href="#todo">B. Notes and todo list for this manual</a></span></dt><dd><dl><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></dd></dl></div>
<div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="_introduction"></a>Introduction</h1></div></div></div>
<p>Git is a fast distributed revision control system.</p>
<p>This manual is designed to be readable by someone with basic UNIX
command-line skills, but no previous knowledge of Git.</p>
<p><a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a> and <a class="xref" href="#exploring-git-history" title="Chapter 2. Exploring Git history">Chapter 2, <i>Exploring Git history</i></a> explain how
to fetch and study a project using git—read these chapters to learn how
to build and test a particular version of a software project, search for
regressions, and so on.</p>
<p>People needing to do actual development will also want to read
<a class="xref" href="#Developing-With-git" title="Chapter 3. Developing with Git">Chapter 3, <i>Developing with Git</i></a> and <a class="xref" href="#sharing-development" title="Chapter 4. Sharing development with others">Chapter 4, <i>Sharing development with others</i></a>.</p>
<p>Further chapters cover more specialized topics.</p>
<p>Comprehensive reference documentation is available through the man
pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command
<code class="literal">git</code> <code class="literal">clone</code> <span class="emphasis"><em><repo></em></span>, you can either use:</p>
<pre class="screen">$ man git-clone</pre>
<p>or:</p>
<pre class="screen">$ git help clone</pre>
<p>With the latter, you can use the manual viewer of your choice; see
<a class="ulink" href="git-help.html" target="_top">git-help(1)</a> for more information.</p>
<p>See also <a class="xref" href="#git-quick-start" title="Appendix A. Git Quick Reference">Appendix A, <i>Git Quick Reference</i></a> for a brief overview of Git commands,
without any explanation.</p>
<p>Finally, see <a class="xref" href="#todo" title="Appendix B. Notes and todo list for this manual">Appendix B, <i>Notes and todo list for this manual</i></a> for ways that you can help make this manual more
complete.</p>
</div>
<div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository"></a>How to get a Git repository</h2></div></div></div>
<p>It will be useful to have a Git repository to experiment with as you
read this manual.</p>
<p>The best way to get one is by using the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> command to
download a copy of an existing repository. If you don’t already have a
project in mind, here are some interesting examples:</p>
<pre class="screen"> # Git itself (approx. 40MB download):
$ git clone git://git.kernel.org/pub/scm/git/git.git
# the Linux kernel (approx. 640MB download):
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git</pre>
<p>The initial clone may be time-consuming for a large project, but you
will only need to clone once.</p>
<p>The clone command creates a new directory named after the project
(<code class="literal">git</code> or <code class="literal">linux</code> in the examples above). After you cd into this
directory, you will see that it contains a copy of the project files,
called the <a class="link" href="#def_working_tree">working tree</a>, together with a special
top-level directory named .<code class="literal">git</code>, which contains all the information
about the history of the project.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-check-out"></a>How to check out a different version of a project</h2></div></div></div>
<p>Git is best thought of as a tool for storing the history of a collection
of files. It stores the history as a compressed collection of
interrelated snapshots of the project’s contents. In Git each such
version is called a <a class="link" href="#def_commit">commit</a>.</p>
<p>Those snapshots aren’t necessarily all arranged in a single line from
oldest to newest; instead, work may simultaneously proceed along
parallel lines of development, called <a class="link" href="#def_branch">branches</a>, which may
merge and diverge.</p>
<p>A single Git repository can track development on multiple branches. It
does this by keeping a list of <a class="link" href="#def_head">heads</a> which reference the
latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows
you the list of branch heads:</p>
<pre class="screen">$ git branch
* master</pre>
<p>A freshly cloned repository contains a single branch head, by default
named "master", with the working directory initialized to the state of
the project referred to by that branch head.</p>
<p>Most projects also use <a class="link" href="#def_tag">tags</a>. Tags, like heads, are
references into the project’s history, and can be listed using the
<a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command:</p>
<pre class="screen">$ git tag -l
v2.6.11
v2.6.11-tree
v2.6.12
v2.6.12-rc2
v2.6.12-rc3
v2.6.12-rc4
v2.6.12-rc5
v2.6.12-rc6
v2.6.13
...</pre>
<p>Tags are expected to always point at the same version of a project,
while heads are expected to advance as development progresses.</p>
<p>Create a new branch head pointing to one of these versions and check it
out using <a class="ulink" href="git-switch.html" target="_top">git-switch(1)</a>:</p>
<pre class="screen">$ git switch -c new v2.6.13</pre>
<p>The working directory then reflects the contents that the project had
when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two
branches, with an asterisk marking the currently checked-out branch:</p>
<pre class="screen">$ git branch
master
* new</pre>
<p>If you decide that you’d rather see version 2.6.17, you can modify
the current branch to point at v2.6.17 instead, with</p>
<pre class="screen">$ git reset --hard v2.6.17</pre>
<p>Note that if the current branch head was your only reference to a
particular point in history, then resetting that branch may leave you
with no way to find the history it used to point to; so use this command
carefully.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="understanding-commits"></a>Understanding History: Commits</h2></div></div></div>
<p>Every change in the history of a project is represented by a commit.
The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the
current branch:</p>
<pre class="screen">$ git show
commit 17cf781661e6d38f737f15f53ab552f1e95960d7
Author: Linus Torvalds <[email protected].(none)>
Date: Tue Apr 19 14:11:06 2005 -0700
Remove duplicate getenv(DB_ENVIRONMENT) call
Noted by Tony Luck.
diff --git a/init-db.c b/init-db.c
index 65898fa..b002dc6 100644
--- a/init-db.c
+++ b/init-db.c
@@ -7,7 +7,7 @@
int main(int argc, char **argv)
{
- char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
+ char *sha1_dir, *path;
int len, i;
if (mkdir(".git", 0755) < 0) {</pre>
<p>As you can see, a commit shows who made the latest change, what they
did, and why.</p>
<p>Every commit has a 40-hexdigit id, sometimes called the "object name" or the
"SHA-1 id", shown on the first line of the <code class="literal">git</code> <code class="literal">show</code> output. You can usually
refer to a commit by a shorter name, such as a tag or a branch name, but this
longer name can also be useful. Most importantly, it is a globally unique
name for this commit: so if you tell somebody else the object name (for
example in email), then you are guaranteed that name will refer to the same
commit in their repository that it does in yours (assuming their repository
has that commit at all). Since the object name is computed as a hash over the
contents of the commit, you are guaranteed that the commit can never change
without its name also changing.</p>
<p>In fact, in <a class="xref" href="#git-concepts" title="Chapter 7. Git concepts">Chapter 7, <i>Git concepts</i></a> we shall see that everything stored in Git
history, including file data and directory contents, is stored in an object
with a name that is a hash of its contents.</p>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="understanding-reachability"></a>Understanding history: commits, parents, and reachability</h3></div></div></div>
<p>Every commit (except the very first commit in a project) also has a
parent commit which shows what happened before this commit.
Following the chain of parents will eventually take you back to the
beginning of the project.</p>
<p>However, the commits do not form a simple list; Git allows lines of
development to diverge and then reconverge, and the point where two
lines of development reconverge is called a "merge". The commit
representing a merge can therefore have more than one parent, with
each parent representing the most recent commit on one of the lines
of development leading to that point.</p>
<p>The best way to see how this works is using the <a class="ulink" href="gitk.html" target="_top">gitk(1)</a>
command; running gitk now on a Git repository and looking for merge
commits will help understand how Git organizes history.</p>
<p>In the following, we say that commit X is "reachable" from commit Y
if commit X is an ancestor of commit Y. Equivalently, you could say
that Y is a descendant of X, or that there is a chain of parents
leading from commit Y to commit X.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="history-diagrams"></a>Understanding history: History diagrams</h3></div></div></div>
<p>We will sometimes represent Git history using diagrams like the one
below. Commits are shown as "o", and the links between them with
lines drawn with - / and \. Time goes left to right:</p>
<pre class="literallayout"> o--o--o <-- Branch A
/
o--o--o <-- master
\
o--o--o <-- Branch B</pre>
<p>If we need to talk about a particular commit, the character "o" may
be replaced with another letter or number.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="what-is-a-branch"></a>Understanding history: What is a branch?</h3></div></div></div>
<p>When we need to be precise, we will use the word "branch" to mean a line
of development, and "branch head" (or just "head") to mean a reference
to the most recent commit on a branch. In the example above, the branch
head named "A" is a pointer to one particular commit, but we refer to
the line of three commits leading up to that point as all being part of
"branch A".</p>
<p>However, when no confusion will result, we often just use the term
"branch" both for branches and for branch heads.</p>
</div>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manipulating-branches"></a>Manipulating branches</h2></div></div></div>
<p>Creating, deleting, and modifying branches is quick and easy; here’s
a summary of the commands:</p>
<div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code></span></dt><dd>
list all branches.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
create a new branch named <span class="emphasis"><em><branch></em></span>, referencing the same
point in history as the current branch.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <span class="emphasis"><em><branch></em></span> <span class="emphasis"><em><start-point></em></span></span></dt><dd>
create a new branch named <span class="emphasis"><em><branch></em></span>, referencing
<span class="emphasis"><em><start-point></em></span>, which may be specified any way you like,
including using a branch name or a tag name.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <code class="literal">-d</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
delete the branch <span class="emphasis"><em><branch></em></span>; if the branch is not fully
merged in its upstream branch or contained in the current branch,
this command will fail with a warning.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <code class="literal">-D</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
delete the branch <span class="emphasis"><em><branch></em></span> irrespective of its merged status.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">switch</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
make the current branch <span class="emphasis"><em><branch></em></span>, updating the working
directory to reflect the version referenced by <span class="emphasis"><em><branch></em></span>.
</dd><dt><span class="term"><code class="literal">git</code> <code class="literal">switch</code> <code class="literal">-c</code> <span class="emphasis"><em><new></em></span> <span class="emphasis"><em><start-point></em></span></span></dt><dd>
create a new branch <span class="emphasis"><em><new></em></span> referencing <span class="emphasis"><em><start-point></em></span>, and
check it out.
</dd></dl></div>
<p>The special symbol "HEAD" can always be used to refer to the current
branch. In fact, Git uses a file named <code class="literal">HEAD</code> in the .<code class="literal">git</code> directory
to remember which branch is current:</p>
<pre class="screen">$ cat .git/HEAD
ref: refs/heads/master</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="detached-head"></a>Examining an old version without creating a new branch</h2></div></div></div>
<p>The <code class="literal">git</code> <code class="literal">switch</code> command normally expects a branch head, but will also
accept an arbitrary commit when invoked with --detach; for example,
you can check out the commit referenced by a tag:</p>
<pre class="screen">$ git switch --detach v2.6.17
Note: checking out 'v2.6.17'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another switch.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command again. Example:
git switch -c new_branch_name
HEAD is now at 427abfa Linux v2.6.17</pre>
<p>The HEAD then refers to the SHA-1 of the commit instead of to a branch,
and git branch shows that you are no longer on a branch:</p>
<pre class="screen">$ cat .git/HEAD
427abfa28afedffadfca9dd8b067eb6d36bac53f
$ git branch
* (detached from v2.6.17)
master</pre>
<p>In this case we say that the HEAD is "detached".</p>
<p>This is an easy way to check out a particular version without having to
make up a name for the new branch. You can still create a new branch
(or tag) for this version later if you decide to.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-remote-branches"></a>Examining branches from a remote repository</h2></div></div></div>
<p>The "master" branch that was created at the time you cloned is a copy
of the HEAD in the repository that you cloned from. That repository
may also have had other branches, though, and your local repository
keeps branches which track each of those remote branches, called
remote-tracking branches, which you
can view using the <code class="literal">-r</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p>
<pre class="screen">$ git branch -r
origin/HEAD
origin/html
origin/maint
origin/man
origin/master
origin/next
origin/seen
origin/todo</pre>
<p>In this example, "origin" is called a remote repository, or "remote"
for short. The branches of this repository are called "remote
branches" from our point of view. The remote-tracking branches listed
above were created based on the remote branches at clone time and will
be updated by <code class="literal">git</code> <code class="literal">fetch</code> (hence <code class="literal">git</code> <code class="literal">pull</code>) and <code class="literal">git</code> <code class="literal">push</code>. See
<a class="xref" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">the section called “Updating a repository with git fetch”</a> for details.</p>
<p>You might want to build on one of these remote-tracking branches
on a branch of your own, just as you would for a tag:</p>
<pre class="screen">$ git switch -c my-todo-copy origin/todo</pre>
<p>You can also check out <code class="literal">origin/todo</code> directly to examine it or
write a one-off patch. See <a class="link" href="#detached-head" title="Examining an old version without creating a new branch">detached head</a>.</p>
<p>Note that the name "origin" is just the name that Git uses by default
to refer to the repository that you cloned from.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div>
<p>Branches, remote-tracking branches, and tags are all references to
commits. All references are named with a slash-separated path name
starting with <code class="literal">refs</code>; the names we’ve been using so far are actually
shorthand:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
The branch <code class="literal">test</code> is short for <code class="literal">refs/heads/test</code>.
</li><li class="listitem">
The tag <code class="literal">v2.6.18</code> is short for <code class="literal">refs/tags/v2.6.18</code>.
</li><li class="listitem">
<code class="literal">origin/master</code> is short for <code class="literal">refs/remotes/origin/master</code>.
</li></ul></div>
<p>The full name is occasionally useful if, for example, there ever
exists a tag and a branch with the same name.</p>
<p>(Newly created refs are actually stored in the .<code class="literal">git/refs</code> directory,
under the path given by their name. However, for efficiency reasons
they may also be packed together in a single file; see
<a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>).</p>
<p>As another useful shortcut, the "HEAD" of a repository can be referred
to just using the name of that repository. So, for example, "origin"
is usually a shortcut for the HEAD branch in the repository "origin".</p>
<p>For the complete list of paths which Git checks for references, and
the order it uses to decide which to choose when there are multiple
references with the same shorthand name, see the "SPECIFYING
REVISIONS" section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-With-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div>
<p>After you clone a repository and commit a few changes of your own, you
may wish to check the original repository for updates.</p>
<p>The <code class="literal">git-fetch</code> command, with no arguments, will update all of the
remote-tracking branches to the latest version found in the original
repository. It will not touch any of your own branches—not even the
"master" branch that was created for you on clone.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-branches"></a>Fetching branches from other repositories</h2></div></div></div>
<p>You can also track branches from repositories other than the one you
cloned from, using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>:</p>
<pre class="screen">$ git remote add staging git://git.kernel.org/.../gregkh/staging.git
$ git fetch staging
...
From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
* [new branch] master -> staging/master
* [new branch] staging-linus -> staging/staging-linus
* [new branch] staging-next -> staging/staging-next</pre>
<p>New remote-tracking branches will be stored under the shorthand name
that you gave <code class="literal">git</code> <code class="literal">remote</code> <code class="literal">add</code>, in this case <code class="literal">staging</code>:</p>
<pre class="screen">$ git branch -r
origin/HEAD -> origin/master
origin/master
staging/master
staging/staging-linus
staging/staging-next</pre>
<p>If you run <code class="literal">git</code> <code class="literal">fetch</code> <span class="emphasis"><em><remote></em></span> later, the remote-tracking branches
for the named <span class="emphasis"><em><remote></em></span> will be updated.</p>
<p>If you examine the file .<code class="literal">git/config</code>, you will see that Git has added
a new stanza:</p>
<pre class="screen">$ cat .git/config
...
[remote "staging"]
url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
fetch = +refs/heads/*:refs/remotes/staging/*
...</pre>
<p>This is what causes Git to track the remote’s branches; you may modify
or delete these configuration options by editing .<code class="literal">git/config</code> with a
text editor. (See the "CONFIGURATION FILE" section of
<a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.)</p>
</div>
</div>
<div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring Git history</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></div>
<p>Git is best thought of as a tool for storing the history of a
collection of files. It does this by storing compressed snapshots of
the contents of a file hierarchy, together with "commits" which show
the relationships between these snapshots.</p>
<p>Git provides extremely flexible and fast tools for exploring the
history of a project.</p>
<p>We start with one specialized tool that is useful for finding the
commit that introduced a bug into a project.</p>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-bisect"></a>How to use bisect to find a regression</h2></div></div></div>
<p>Suppose version 2.6.18 of your project worked, but the version at
"master" crashes. Sometimes the best way to find the cause of such a
regression is to perform a brute-force search through the project’s
history to find the particular commit that caused the problem. The
<a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p>
<pre class="screen">$ git bisect start
$ git bisect good v2.6.18
$ git bisect bad master
Bisecting: 3537 revisions left to test after this
[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</pre>
<p>If you run <code class="literal">git</code> <code class="literal">branch</code> at this point, you’ll see that Git has
temporarily moved you in "(no branch)". HEAD is now detached from any
branch and points directly to a commit (with commit id 65934) that
is reachable from "master" but not from v2.6.18. Compile and test it,
and see whether it crashes. Assume it does crash. Then:</p>
<pre class="screen">$ git bisect bad
Bisecting: 1769 revisions left to test after this
[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</pre>
<p>checks out an older version. Continue like this, telling Git at each
stage whether the version it gives you is good or bad, and notice
that the number of revisions left to test is cut approximately in
half each time.</p>
<p>After about 13 tests (in this case), it will output the commit id of
the guilty commit. You can then examine the commit with
<a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug
report with the commit id. Finally, run</p>
<pre class="screen">$ git bisect reset</pre>
<p>to return you to the branch you were on before.</p>
<p>Note that the version which <code class="literal">git</code> <code class="literal">bisect</code> checks out for you at each
point is just a suggestion, and you’re free to try a different
version if you think it would be a good idea. For example,
occasionally you may land on a commit that broke something unrelated;
run</p>
<pre class="screen">$ git bisect visualize</pre>
<p>which will run gitk and label the commit it chose with a marker that
says "bisect". Choose a safe-looking commit nearby, note its commit
id, and check it out with:</p>
<pre class="screen">$ git reset --hard fb47ddb2db</pre>
<p>then test, run <code class="literal">bisect</code> <code class="literal">good</code> or <code class="literal">bisect</code> <code class="literal">bad</code> as appropriate, and
continue.</p>
<p>Instead of <code class="literal">git</code> <code class="literal">bisect</code> <code class="literal">visualize</code> and then <code class="literal">git</code> <code class="literal">reset</code> <code class="literal">--hard</code>
<code class="literal">fb47ddb2db</code>, you might just want to tell Git that you want to skip
the current commit:</p>
<pre class="screen">$ git bisect skip</pre>
<p>In this case, though, Git may not eventually be able to tell the first
bad one between some first skipped commits and a later bad commit.</p>
<p>There are also ways to automate the bisecting process if you have a
test script that can tell a good from a bad commit. See
<a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other <code class="literal">git</code>
<code class="literal">bisect</code> features.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="naming-commits"></a>Naming commits</h2></div></div></div>
<p>We have seen several ways of naming commits already:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
40-hexdigit object name
</li><li class="listitem">
branch name: refers to the commit at the head of the given
branch
</li><li class="listitem">
tag name: refers to the commit pointed to by the given tag
(we’ve seen branches and tags are special cases of
<a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>).
</li><li class="listitem">
HEAD: refers to the head of the current branch
</li></ul></div>
<p>There are many more; see the "SPECIFYING REVISIONS" section of the
<a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> man page for the complete list of ways to
name revisions. Some examples:</p>
<pre class="screen">$ git show fb47ddb2 # the first few characters of the object name
# are usually enough to specify it uniquely
$ git show HEAD^ # the parent of the HEAD commit
$ git show HEAD^^ # the grandparent
$ git show HEAD~4 # the great-great-grandparent</pre>
<p>Recall that merge commits may have more than one parent; by default,
<code class="literal">^</code> and <code class="literal">~</code> follow the first parent listed in the commit, but you can
also choose:</p>
<pre class="screen">$ git show HEAD^1 # show the first parent of HEAD
$ git show HEAD^2 # show the second parent of HEAD</pre>
<p>In addition to HEAD, there are several other special names for
commits:</p>
<p>Merges (to be discussed later), as well as operations such as
<code class="literal">git</code> <code class="literal">reset</code>, which change the currently checked-out commit, generally
set ORIG_HEAD to the value HEAD had before the current operation.</p>
<p>The <code class="literal">git</code> <code class="literal">fetch</code> operation always stores the head of the last fetched
branch in FETCH_HEAD. For example, if you run <code class="literal">git</code> <code class="literal">fetch</code> without
specifying a local branch as the target of the operation</p>
<pre class="screen">$ git fetch git://example.com/proj.git theirbranch</pre>
<p>the fetched commits will still be available from FETCH_HEAD.</p>
<p>When we discuss merges we’ll also see the special name MERGE_HEAD,
which refers to the other branch that we’re merging in to the current
branch.</p>
<p>The <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is
occasionally useful for translating some name for a commit to the object
name for that commit:</p>
<pre class="screen">$ git rev-parse origin
e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-tags"></a>Creating tags</h2></div></div></div>
<p>We can also create a tag to refer to a particular commit; after
running</p>
<pre class="screen">$ git tag stable-1 1b2e1d63ff</pre>
<p>You can use <code class="literal">stable-1</code> to refer to the commit 1b2e1d63ff.</p>
<p>This creates a "lightweight" tag. If you would also like to include a
comment with the tag, and possibly sign it cryptographically, then you
should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page
for details.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="browsing-revisions"></a>Browsing revisions</h2></div></div></div>
<p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its
own, it shows all commits reachable from the parent commit; but you
can also make more specific requests:</p>
<pre class="screen">$ git log v2.5.. # commits since (not reachable from) v2.5
$ git log test..master # commits reachable from master but not test
$ git log master..test # ...reachable from test but not master
$ git log master...test # ...reachable from either test or master,
# but not both
$ git log --since="2 weeks ago" # commits from the last 2 weeks
$ git log Makefile # commits which modify Makefile
$ git log fs/ # ... which modify any file under fs/
$ git log -S'foo()' # commits which add or remove any file data
# matching the string 'foo()'</pre>
<p>And of course you can combine all of these; the following finds
commits since v2.5 which touch the <code class="literal">Makefile</code> or any file under <code class="literal">fs</code>:</p>
<pre class="screen">$ git log v2.5.. Makefile fs/</pre>
<p>You can also ask git log to show patches:</p>
<pre class="screen">$ git log -p</pre>
<p>See the <code class="literal">--pretty</code> option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more
display options.</p>
<p>Note that git log starts with the most recent commit and works
backwards through the parents; however, since Git history can contain
multiple independent lines of development, the particular order that
commits are listed in may be somewhat arbitrary.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generating-diffs"></a>Generating diffs</h2></div></div></div>
<p>You can generate diffs between any two versions using
<a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>:</p>
<pre class="screen">$ git diff master..test</pre>
<p>That will produce the diff between the tips of the two branches. If
you’d prefer to find the diff from their common ancestor to test, you
can use three dots instead of two:</p>
<pre class="screen">$ git diff master...test</pre>
<p>Sometimes what you want instead is a set of patches; for this you can
use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>:</p>
<pre class="screen">$ git format-patch master..test</pre>
<p>will generate a file with a patch for each commit reachable from test
but not from master.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="viewing-old-file-versions"></a>Viewing old file versions</h2></div></div></div>
<p>You can always view an old version of a file by just checking out the
correct revision first. But sometimes it is more convenient to be
able to view an old version of a single file without checking
anything out; this command does that:</p>
<pre class="screen">$ git show v2.5:fs/locks.c</pre>
<p>Before the colon may be anything that names a commit, and after it
may be any path to a file tracked by Git.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="counting-commits-on-a-branch"></a>Counting the number of commits on a branch</h3></div></div></div>
<p>Suppose you want to know how many commits you’ve made on <code class="literal">mybranch</code>
since it diverged from <code class="literal">origin</code>:</p>
<pre class="screen">$ git log --pretty=oneline origin..mybranch | wc -l</pre>
<p>Alternatively, you may often see this sort of thing done with the
lower-level command <a class="ulink" href="git-rev-list.html" target="_top">git-rev-list(1)</a>, which just lists the SHA-1’s
of all the given commits:</p>
<pre class="screen">$ git rev-list origin..mybranch | wc -l</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-equal-branches"></a>Check whether two branches point at the same history</h3></div></div></div>
<p>Suppose you want to check whether two branches point at the same point
in history.</p>
<pre class="screen">$ git diff origin..master</pre>
<p>will tell you whether the contents of the project are the same at the
two branches; in theory, however, it’s possible that the same project
contents could have been arrived at by two different historical
routes. You could compare the object names:</p>
<pre class="screen">$ git rev-list origin
e05db0fd4f31dde7005f075a84f96b360d05984b
$ git rev-list master
e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
<p>Or you could recall that the ... operator selects all commits
reachable from either one reference or the other but not
both; so</p>
<pre class="screen">$ git log origin...master</pre>
<p>will return no commits when the two branches are equal.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="finding-tagged-descendants"></a>Find first tagged version including a given fix</h3></div></div></div>
<p>Suppose you know that the commit e05db0fd fixed a certain problem.
You’d like to find the earliest tagged release that contains that
fix.</p>
<p>Of course, there may be more than one answer—if the history branched
after commit e05db0fd, then there could be multiple "earliest" tagged
releases.</p>
<p>You could just visually inspect the commits since e05db0fd:</p>
<pre class="screen">$ gitk e05db0fd..</pre>
<p>or you can use <a class="ulink" href="git-name-rev.html" target="_top">git-name-rev(1)</a>, which will give the commit a
name based on any tag it finds pointing to one of the commit’s
descendants:</p>
<pre class="screen">$ git name-rev --tags e05db0fd
e05db0fd tags/v1.5.0-rc1^0~23</pre>
<p>The <a class="ulink" href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the
revision using a tag on which the given commit is based:</p>
<pre class="screen">$ git describe e05db0fd
v1.5.0-rc0-260-ge05db0f</pre>
<p>but that may sometimes help you guess which tags might come after the
given commit.</p>
<p>If you just want to verify whether a given tagged version contains a
given commit, you could use <a class="ulink" href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p>
<pre class="screen">$ git merge-base e05db0fd v1.5.0-rc1
e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
<p>The merge-base command finds a common ancestor of the given commits,
and always returns one or the other in the case where one is a
descendant of the other; so the above output shows that e05db0fd
actually is an ancestor of v1.5.0-rc1.</p>
<p>Alternatively, note that</p>
<pre class="screen">$ git log v1.5.0-rc1..e05db0fd</pre>
<p>will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
because it outputs only commits that are not reachable from v1.5.0-rc1.</p>
<p>As yet another alternative, the <a class="ulink" href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists
the commits reachable from its arguments with a display on the left-hand
side that indicates which arguments that commit is reachable from.
So, if you run something like</p>
<pre class="screen">$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
available
! [v1.5.0-rc0] GIT v1.5.0 preview
! [v1.5.0-rc1] GIT v1.5.0-rc1
! [v1.5.0-rc2] GIT v1.5.0-rc2
...</pre>
<p>then a line like</p>
<pre class="screen">+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
available</pre>
<p>shows that e05db0fd is reachable from itself, from v1.5.0-rc1,
and from v1.5.0-rc2, and not from v1.5.0-rc0.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="showing-commits-unique-to-a-branch"></a>Showing commits unique to a given branch</h3></div></div></div>
<p>Suppose you would like to see all the commits reachable from the branch
head named <code class="literal">master</code> but not from any other head in your repository.</p>
<p>We can list all the heads in this repository with
<a class="ulink" href="git-show-ref.html" target="_top">git-show-ref(1)</a>:</p>
<pre class="screen">$ git show-ref --heads
bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes</pre>
<p>We can get just the branch-head names, and remove <code class="literal">master</code>, with
the help of the standard utilities cut and grep:</p>
<pre class="screen">$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
refs/heads/core-tutorial
refs/heads/maint
refs/heads/tutorial-2
refs/heads/tutorial-fixes</pre>
<p>And then we can ask to see all the commits reachable from master
but not from these other heads:</p>
<pre class="screen">$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
grep -v '^refs/heads/master' )</pre>
<p>Obviously, endless variations are possible; for example, to see all
commits reachable from some head but not from any tag in the repository:</p>
<pre class="screen">$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )</pre>
<p>(See <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for explanations of commit-selecting
syntax such as <code class="literal">--not</code>.)</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div>
<p>The <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from
any version of a project; for example:</p>
<pre class="screen">$ git archive -o latest.tar.gz --prefix=project/ HEAD</pre>
<p>will use HEAD to produce a gzipped tar archive in which each filename
is preceded by <code class="literal">project/</code>. The output file format is inferred from
the output file extension if possible, see <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> for
details.</p>
<p>Versions of Git older than 1.7.7 don’t know about the <code class="literal">tar.gz</code> format,
you’ll need to use gzip explicitly:</p>
<pre class="screen">$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz</pre>
<p>If you’re releasing a new version of a software project, you may want
to simultaneously make a changelog to include in the release
announcement.</p>
<p>Linus Torvalds, for example, makes new kernel releases by tagging them,
then running:</p>
<pre class="screen">$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7</pre>
<p>where release-script is a shell script that looks like:</p>
<pre class="screen">#!/bin/sh
stable="$1"
last="$2"
new="$3"
echo "# git tag v$new"
echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"</pre>
<p>and then he just cut-and-pastes the output commands after verifying that
they look OK.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="Finding-commits-With-given-Content"></a>Finding commits referencing a file with given content</h3></div></div></div>
<p>Somebody hands you a copy of a file, and asks which commits modified a
file such that it contained the given content either before or after the
commit. You can find out with this:</p>
<pre class="screen">$ git log --raw --abbrev=40 --pretty=oneline |
grep -B 1 `git hash-object filename`</pre>
<p>Figuring out why this works is left as an exercise to the (advanced)
student. The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a>, <a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>, and
<a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a> man pages may prove helpful.</p>
</div>
</div>
</div>
<div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="Developing-With-git"></a>Chapter 3. Developing with Git</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="telling-git-your-name"></a>Telling Git your name</h2></div></div></div>
<p>Before creating any commits, you should introduce yourself to Git.
The easiest way to do so is to use <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p>
<pre class="screen">$ git config --global user.name 'Your Name Comes Here'
$ git config --global user.email '[email protected]'</pre>
<p>Which will add the following to a file named .<code class="literal">gitconfig</code> in your
home directory:</p>
<pre class="screen">[user]
name = Your Name Comes Here
email = [email protected]</pre>
<p>See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
details on the configuration file. The file is plain text, so you can
also edit it with your favorite editor.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-a-new-repository"></a>Creating a new repository</h2></div></div></div>
<p>Creating a new repository from scratch is very easy:</p>
<pre class="screen">$ mkdir project
$ cd project
$ git init</pre>
<p>If you have some initial content (say, a tarball):</p>
<pre class="screen">$ tar xzvf project.tar.gz
$ cd project
$ git init
$ git add . # include everything below ./ in the first commit:
$ git commit</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-make-a-commit"></a>How to make a commit</h2></div></div></div>
<p>Creating a new commit takes three steps:</p>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
Making some changes to the working directory using your
favorite editor.
</li><li class="listitem">
Telling Git about your changes.
</li><li class="listitem">
Creating the commit using the content you told Git about
in step 2.
</li></ol></div>
<p>In practice, you can interleave and repeat steps 1 and 2 as many
times as you want: in order to keep track of what you want committed
at step 3, Git maintains a snapshot of the tree’s contents in a
special staging area called "the index."</p>
<p>At the beginning, the content of the index will be identical to
that of the HEAD. The command <code class="literal">git</code> <code class="literal">diff</code> <code class="literal">--cached</code>, which shows
the difference between the HEAD and the index, should therefore
produce no output at that point.</p>
<p>Modifying the index is easy:</p>
<p>To update the index with the contents of a new or modified file, use</p>
<pre class="screen">$ git add path/to/file</pre>
<p>To remove a file from the index and from the working tree, use</p>
<pre class="screen">$ git rm path/to/file</pre>
<p>After each step you can verify that</p>
<pre class="screen">$ git diff --cached</pre>
<p>always shows the difference between the HEAD and the index file—this
is what you’d commit if you created the commit now—and that</p>
<pre class="screen">$ git diff</pre>
<p>shows the difference between the working tree and the index file.</p>
<p>Note that <code class="literal">git</code> <code class="literal">add</code> always adds just the current contents of a file
to the index; further changes to the same file will be ignored unless
you run <code class="literal">git</code> <code class="literal">add</code> on the file again.</p>
<p>When you’re ready, just run</p>
<pre class="screen">$ git commit</pre>
<p>and Git will prompt you for a commit message and then create the new
commit. Check to make sure it looks like what you expected with</p>
<pre class="screen">$ git show</pre>
<p>As a special shortcut,</p>
<pre class="screen">$ git commit -a</pre>
<p>will update the index with any files that you’ve modified or removed
and create a commit, all in one step.</p>
<p>A number of commands are useful for keeping track of what you’re
about to commit:</p>
<pre class="screen">$ git diff --cached # difference between HEAD and the index; what
# would be committed if you ran "commit" now.
$ git diff # difference between the index file and your
# working directory; changes that would not
# be included if you ran "commit" now.
$ git diff HEAD # difference between HEAD and working tree; what
# would be committed if you ran "commit -a" now.
$ git status # a brief per-file summary of the above.</pre>
<p>You can also use <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> to create commits, view changes in
the index and the working tree files, and individually select diff hunks
for inclusion in the index (by right-clicking on the diff hunk and
choosing "Stage Hunk For Commit").</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-good-commit-messages"></a>Creating good commit messages</h2></div></div></div>
<p>Though not required, it’s a good idea to begin the commit message
with a single short (no more than 50 characters) line summarizing the
change, followed by a blank line and then a more thorough
description. The text up to the first blank line in a commit
message is treated as the commit title, and that title is used
throughout Git. For example, <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a> turns a
commit into email, and it uses the title on the Subject line and the
rest of the commit in the body.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ignoring-files"></a>Ignoring files</h2></div></div></div>
<p>A project will often generate files that you do <span class="emphasis"><em>not</em></span> want to track with Git.
This typically includes files generated by a build process or temporary
backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with Git
is just a matter of <span class="emphasis"><em>not</em></span> calling <code class="literal">git</code> <code class="literal">add</code> on them. But it quickly becomes
annoying to have these untracked files lying around; e.g. they make
<code class="literal">git</code> <code class="literal">add</code> . practically useless, and they keep showing up in the output of
<code class="literal">git</code> <code class="literal">status</code>.</p>
<p>You can tell Git to ignore certain files by creating a file called
.<code class="literal">gitignore</code> in the top level of your working directory, with contents
such as:</p>
<pre class="screen"># Lines starting with '#' are considered comments.
# Ignore any file named foo.txt.
foo.txt
# Ignore (generated) html files,
*.html
# except foo.html which is maintained by hand.
!foo.html
# Ignore objects and archives.
*.[oa]</pre>
<p>See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for a detailed explanation of the syntax. You can
also place .gitignore files in other directories in your working tree, and they
will apply to those directories and their subdirectories. The .<code class="literal">gitignore</code>
files can be added to your repository like any other files (just run <code class="literal">git</code> <code class="literal">add</code>
<code class="literal">.gitignore</code> and <code class="literal">git</code> <code class="literal">commit</code>, as usual), which is convenient when the exclude
patterns (such as patterns matching build output files) would also make sense
for other users who clone your repository.</p>
<p>If you wish the exclude patterns to affect only certain repositories
(instead of every repository for a given project), you may instead put
them in a file in your repository named .<code class="literal">git/info/exclude</code>, or in any
file specified by the <code class="literal">core.excludesFile</code> configuration variable.
Some Git commands can also take exclude patterns directly on the
command line. See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for the details.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-merge"></a>How to merge</h2></div></div></div>
<p>You can rejoin two diverging branches of development using
<a class="ulink" href="git-merge.html" target="_top">git-merge(1)</a>:</p>
<pre class="screen">$ git merge branchname</pre>
<p>merges the development in the branch <code class="literal">branchname</code> into the current
branch.</p>
<p>A merge is made by combining the changes made in <code class="literal">branchname</code> and the
changes made up to the latest commit in your current branch since
their histories forked. The work tree is overwritten by the result of
the merge when this combining is done cleanly, or overwritten by a
half-merged results when this combining results in conflicts.
Therefore, if you have uncommitted changes touching the same files as
the ones impacted by the merge, Git will refuse to proceed. Most of
the time, you will want to commit your changes before you can merge,
and if you don’t, then <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> can take these changes
away while you’re doing the merge, and reapply them afterwards.</p>
<p>If the changes are independent enough, Git will automatically complete
the merge and commit the result (or reuse an existing commit in case
of <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>, see below). On the other hand,
if there are conflicts—for example, if the same file is
modified in two different ways in the remote branch and the local
branch—then you are warned; the output may look something like this:</p>
<pre class="screen">$ git merge next
100% (4/4) done
Auto-merged file.txt
CONFLICT (content): Merge conflict in file.txt
Automatic merge failed; fix conflicts and then commit the result.</pre>
<p>Conflict markers are left in the problematic files, and after
you resolve the conflicts manually, you can update the index
with the contents and run Git commit, as you normally would when
creating a new file.</p>
<p>If you examine the resulting commit using gitk, you will see that it
has two parents, one pointing to the top of the current branch, and
one to the top of the other branch.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="resolving-a-merge"></a>Resolving a merge</h2></div></div></div>
<p>When a merge isn’t resolved automatically, Git leaves the index and
the working tree in a special state that gives you all the
information you need to help resolve the merge.</p>
<p>Files with conflicts are marked specially in the index, so until you
resolve the problem and update the index, <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> will
fail:</p>
<pre class="screen">$ git commit
file.txt: needs merge</pre>
<p>Also, <a class="ulink" href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the
files with conflicts will have conflict markers added, like this:</p>
<pre class="screen"><<<<<<< HEAD:file.txt
Hello world
=======
Goodbye
>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</pre>
<p>All you need to do is edit the files to resolve the conflicts, and then</p>
<pre class="screen">$ git add file.txt
$ git commit</pre>
<p>Note that the commit message will already be filled in for you with
some information about the merge. Normally you can just use this
default message unchanged, but you may add additional commentary of
your own if desired.</p>
<p>The above is all you need to know to resolve a simple merge. But Git
also provides more information to help resolve conflicts:</p>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="conflict-resolution"></a>Getting conflict-resolution help during a merge</h3></div></div></div>
<p>All of the changes that Git was able to merge automatically are
already added to the index file, so <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> shows only
the conflicts. It uses an unusual syntax:</p>
<pre class="screen">$ git diff
diff --cc file.txt
index 802992c,2b60207..0000000
--- a/file.txt
+++ b/file.txt
@@@ -1,1 -1,1 +1,5 @@@
++<<<<<<< HEAD:file.txt
+Hello world
++=======
+ Goodbye
++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</pre>
<p>Recall that the commit which will be committed after we resolve this
conflict will have two parents instead of the usual one: one parent
will be HEAD, the tip of the current branch; the other will be the
tip of the other branch, which is stored temporarily in MERGE_HEAD.</p>
<p>During the merge, the index holds three versions of each file. Each of
these three "file stages" represents a different version of the file:</p>
<pre class="screen">$ git show :1:file.txt # the file in a common ancestor of both branches
$ git show :2:file.txt # the version from HEAD.
$ git show :3:file.txt # the version from MERGE_HEAD.</pre>
<p>When you ask <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the conflicts, it runs a
three-way diff between the conflicted merge results in the work tree with
stages 2 and 3 to show only hunks whose contents come from both sides,
mixed (in other words, when a hunk’s merge results come only from stage 2,
that part is not conflicting and is not shown. Same for stage 3).</p>
<p>The diff above shows the differences between the working-tree version of
file.txt and the stage 2 and stage 3 versions. So instead of preceding
each line by a single <code class="literal">+</code> or <code class="literal">-</code>, it now uses two columns: the first
column is used for differences between the first parent and the working
directory copy, and the second for differences between the second parent
and the working directory copy. (See the "COMBINED DIFF FORMAT" section
of <a class="ulink" href="git-diff-files.html" target="_top">git-diff-files(1)</a> for a details of the format.)</p>
<p>After resolving the conflict in the obvious way (but before updating the
index), the diff will look like:</p>
<pre class="screen">$ git diff
diff --cc file.txt
index 802992c,2b60207..0000000
--- a/file.txt
+++ b/file.txt
@@@ -1,1 -1,1 +1,1 @@@
- Hello world
-Goodbye
++Goodbye world</pre>
<p>This shows that our resolved version deleted "Hello world" from the
first parent, deleted "Goodbye" from the second parent, and added
"Goodbye world", which was previously absent from both.</p>
<p>Some special diff options allow diffing the working directory against
any of these stages:</p>
<pre class="screen">$ git diff -1 file.txt # diff against stage 1
$ git diff --base file.txt # same as the above
$ git diff -2 file.txt # diff against stage 2
$ git diff --ours file.txt # same as the above
$ git diff -3 file.txt # diff against stage 3
$ git diff --theirs file.txt # same as the above.</pre>
<p>When using the <span class="emphasis"><em>ort</em></span> merge strategy (the default), before updating the working
tree with the result of the merge, Git writes a ref named AUTO_MERGE
reflecting the state of the tree it is about to write. Conflicted paths with
textual conflicts that could not be automatically merged are written to this
tree with conflict markers, just as in the working tree. AUTO_MERGE can thus be
used with <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the changes you’ve made so far to resolve
conflicts. Using the same example as above, after resolving the conflict we
get:</p>
<pre class="screen">$ git diff AUTO_MERGE
diff --git a/file.txt b/file.txt
index cd10406..8bf5ae7 100644
--- a/file.txt
+++ b/file.txt
@@ -1,5 +1 @@
-<<<<<<< HEAD:file.txt
-Hello world
-=======
-Goodbye
->>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
+Goodbye world</pre>
<p>Notice that the diff shows we deleted the conflict markers and both versions of
the content line, and wrote "Goodbye world" instead.</p>
<p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> and <a class="ulink" href="gitk.html" target="_top">gitk(1)</a> commands also provide special help
for merges:</p>
<pre class="screen">$ git log --merge
$ gitk --merge</pre>
<p>These will display all commits which exist only on HEAD or on
MERGE_HEAD, and which touch an unmerged file.</p>
<p>You may also use <a class="ulink" href="git-mergetool.html" target="_top">git-mergetool(1)</a>, which lets you merge the
unmerged files using external tools such as Emacs or kdiff3.</p>
<p>Each time you resolve the conflicts in a file and update the index:</p>
<pre class="screen">$ git add file.txt</pre>
<p>the different stages of that file will be "collapsed", after which
<code class="literal">git</code> <code class="literal">diff</code> will (by default) no longer show diffs for that file.</p>
</div>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="undoing-a-merge"></a>Undoing a merge</h2></div></div></div>
<p>If you get stuck and decide to just give up and throw the whole mess
away, you can always return to the pre-merge state with</p>
<pre class="screen">$ git merge --abort</pre>
<p>Or, if you’ve already committed the merge that you want to throw away,</p>
<pre class="screen">$ git reset --hard ORIG_HEAD</pre>
<p>However, this last command can be dangerous in some cases—never
throw away a commit you have already committed if that commit may
itself have been merged into another branch, as doing so may confuse
further merges.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fast-forwards"></a>Fast-forward merges</h2></div></div></div>
<p>There is one special case not mentioned above, which is treated
differently. Normally, a merge results in a merge commit, with two
parents, one pointing at each of the two lines of development that
were merged.</p>
<p>However, if the current branch is an ancestor of the other—so every commit
present in the current branch is already contained in the other branch—then Git
just performs a "fast-forward"; the head of the current branch is moved forward
to point at the head of the merged-in branch, without any new commits being
created.</p>
</div>
<div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fixing-mistakes"></a>Fixing mistakes</h2></div></div></div>
<p>If you’ve messed up the working tree, but haven’t yet committed your
mistake, you can return the entire working tree to the last committed