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2 <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User’s Manual (for version 1.5.3 or newer)</title><link rel="stylesheet" href="docbook-xsl.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book" title="Git User’s Manual (for version 1.5.3 or newer)"><div class="titlepage"><div><div><h1 class="title"><a name="id372401"></a>Git User’s Manual (for version 1.5.3 or newer)</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="preface"><a href="#id372327"></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="#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="#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><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></dl></div><div class="preface"><div class="titlepage"><div><div><h2 class="title"><a name="id372327"></a></h2></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
3 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
4 to fetch and study a project using git—read these chapters to learn how
5 to build and test a particular version of a software project, search for
6 regressions, and so on.</p><p>People needing to do actual development will also want to read
7 <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
8 pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command
9 "git clone <repo>", you can either use:</p><div class="literallayout"><p>$ man git-clone</p></div><p>or:</p><div class="literallayout"><p>$ git help clone</p></div><p>With the latter, you can use the manual viewer of your choice; see
10 <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,
11 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
12 complete.</p></div><div class="chapter" title="Chapter 1. Repositories and Branches"><div class="titlepage"><div><div><h2 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><div class="section" title="How to get a git repository"><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
13 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
14 download a copy of an existing repository. If you don’t already have a
15 project in mind, here are some interesting examples:</p><div class="literallayout"><p> # git itself (approx. 10MB download):<br>
16 $ git clone git://git.kernel.org/pub/scm/git/git.git<br>
18 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git</p></div><p>The initial clone may be time-consuming for a large project, but you
19 will only need to clone once.</p><p>The clone command creates a new directory named after the project ("git"
20 or "linux-2.6" in the examples above). After you cd into this
21 directory, you will see that it contains a copy of the project files,
23 top-level directory named ".git", which contains all the information
24 about the history of the project.</p></div><div class="section" title="How to check out a different version of a project"><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
25 of files. It stores the history as a compressed collection of
26 interrelated snapshots of the project’s contents. In git each such
27 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
28 oldest to newest; instead, work may simultaneously proceed along
30 merge and diverge.</p><p>A single git repository can track development on multiple branches. It
32 latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows
34 * master</p></div><p>A freshly cloned repository contains a single branch head, by default
35 named "master", with the working directory initialized to the state of
36 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
37 references into the project’s history, and can be listed using the
38 <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command:</p><div class="literallayout"><p>$ git tag -l<br>
48 ...</p></div><p>Tags are expected to always point at the same version of a project,
49 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
50 out using <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>:</p><div class="literallayout"><p>$ git checkout -b new v2.6.13</p></div><p>The working directory then reflects the contents that the project had
51 when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two
52 branches, with an asterisk marking the currently checked-out branch:</p><div class="literallayout"><p>$ git branch<br>
53 master<br>
55 the current branch to point at v2.6.17 instead, with</p><div class="literallayout"><p>$ git reset --hard v2.6.17</p></div><p>Note that if the current branch head was your only reference to a
56 particular point in history, then resetting that branch may leave you
57 with no way to find the history it used to point to; so use this command
58 carefully.</p></div><div class="section" title="Understanding History: Commits"><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.
59 The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the
64 <br>
65 Remove duplicate getenv(DB_ENVIRONMENT) call<br>
66 <br>
67 Noted by Tony Luck.<br>
68 <br>
69 diff --git a/init-db.c b/init-db.c<br>
71 --- a/init-db.c<br>
72 +++ b/init-db.c<br>
74 <br>
75 int main(int argc, char **argv)<br>
76 {<br>
77 - char *sha1_dir = getenv(DB_ENVIRONMENT), *path;<br>
78 + char *sha1_dir, *path;<br>
79 int len, i;<br>
80 <br>
81 if (mkdir(".git", 0755) < 0) {</p></div><p>As you can see, a commit shows who made the latest change, what they
84 refer to a commit by a shorter name, such as a tag or a branch name, but this
85 longer name can also be useful. Most importantly, it is a globally unique
86 name for this commit: so if you tell somebody else the object name (for
87 example in email), then you are guaranteed that name will refer to the same
88 commit in their repository that it does in yours (assuming their repository
89 has that commit at all). Since the object name is computed as a hash over the
90 contents of the commit, you are guaranteed that the commit can never change
91 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
92 history, including file data and directory contents, is stored in an object
93 with a name that is a hash of its contents.</p><div class="section" title="Understanding history: commits, parents, and reachability"><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
94 parent commit which shows what happened before this commit.
95 Following the chain of parents will eventually take you back to the
96 beginning of the project.</p><p>However, the commits do not form a simple list; git allows lines of
97 development to diverge and then reconverge, and the point where two
98 lines of development reconverge is called a "merge". The commit
99 representing a merge can therefore have more than one parent, with
100 each parent representing the most recent commit on one of the lines
101 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>
102 command; running gitk now on a git repository and looking for merge
103 commits will help understand how the git organizes history.</p><p>In the following, we say that commit X is "reachable" from commit Y
104 if commit X is an ancestor of commit Y. Equivalently, you could say
105 that Y is a descendant of X, or that there is a chain of parents
106 leading from commit Y to commit X.</p></div><div class="section" title="Understanding history: History diagrams"><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
107 below. Commits are shown as "o", and the links between them with
108 lines drawn with - / and \. Time goes left to right:</p><pre class="literallayout"> o--o--o <-- Branch A
109 /
110 o--o--o <-- master
111 \
112 o--o--o <-- Branch B</pre><p>If we need to talk about a particular commit, the character "o" may
113 be replaced with another letter or number.</p></div><div class="section" title="Understanding history: What is a branch?"><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
115 to the most recent commit on a branch. In the example above, the branch
116 head named "A" is a pointer to one particular commit, but we refer to
117 the line of three commits leading up to that point as all being part of
119 "branch" both for branches and for branch heads.</p></div></div><div class="section" title="Manipulating branches"><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
121 git branch
122 </span></dt><dd>
123 list all branches
126 </span></dt><dd>
128 point in history as the current branch
131 </span></dt><dd>
134 including using a branch name or a tag name
137 </span></dt><dd>
139 points to a commit which is not reachable from the current
140 branch, this command will fail with a warning.
143 </span></dt><dd>
144 even if the branch points to a commit not reachable
145 from the current branch, you may know that that commit
146 is still reachable from some other branch or tag. In that
147 case it is safe to use this command to force git to delete
148 the branch.
151 </span></dt><dd>
156 </span></dt><dd>
158 check it out.
160 branch. In fact, git uses a file named "HEAD" in the .git directory to
162 ref: refs/heads/master</p></div></div><div class="section" title="Examining an old version without creating a new branch"><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 checkout</code> command normally expects a branch head, but will also
163 accept an arbitrary commit; for example, you can check out the commit
166 If you want to create a new branch from this checkout, you may do so<br>
167 (now or later) by using -b with the checkout command again. Example:<br>
169 HEAD is now at 427abfa... Linux v2.6.17</p></div><p>The HEAD then refers to the SHA-1 of the commit instead of to a branch,
170 and git branch shows that you are no longer on a branch:</p><div class="literallayout"><p>$ cat .git/HEAD<br>
172 $ git branch<br>
173 * (no branch)<br>
174 master</p></div><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
175 make up a name for the new branch. You can still create a new branch
176 (or tag) for this version later if you decide to.</p></div><div class="section" title="Examining branches from a remote repository"><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
177 of the HEAD in the repository that you cloned from. That repository
178 may also have had other branches, though, and your local repository
179 keeps branches which track each of those remote branches, called
180 remote-tracking branches, which you
181 can view using the "-r" option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p><div class="literallayout"><p>$ git branch -r<br>
182 origin/HEAD<br>
183 origin/html<br>
184 origin/maint<br>
185 origin/man<br>
186 origin/master<br>
187 origin/next<br>
188 origin/pu<br>
190 for short. The branches of this repository are called "remote
191 branches" from our point of view. The remote-tracking branches listed
192 above were created based on the remote branches at clone time and will
194 <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
195 on a branch of your own, just as you would for a tag:</p><div class="literallayout"><p>$ git checkout -b my-todo-copy origin/todo</p></div><p>You can also check out "origin/todo" directly to examine it or
196 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
197 to refer to the repository that you cloned from.</p></div><div class="section" title="Naming branches, tags, and other references"><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
198 commits. All references are named with a slash-separated path name
199 starting with "refs"; the names we’ve been using so far are actually
200 shorthand:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
206 </li></ul></div><p>The full name is occasionally useful if, for example, there ever
207 exists a tag and a branch with the same name.</p><p>(Newly created refs are actually stored in the .git/refs directory,
208 under the path given by their name. However, for efficiency reasons
209 they may also be packed together in a single file; see
210 <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
211 to just using the name of that repository. So, for example, "origin"
212 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
213 the order it uses to decide which to choose when there are multiple
214 references with the same shorthand name, see the "SPECIFYING
215 REVISIONS" section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>.</p></div><div class="section" title="Updating a repository with git fetch"><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>Eventually the developer cloned from will do additional work in her
216 repository, creating new commits and advancing the branches to point
218 remote-tracking branches to the latest version found in her
219 repository. It will not touch any of your own branches—not even the
220 "master" branch that was created for you on clone.</p></div><div class="section" title="Fetching branches from other repositories"><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
221 cloned from, using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>:</p><div class="literallayout"><p>$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git<br>
222 $ git fetch linux-nfs<br>
223 * refs/remotes/linux-nfs/master: storing branch 'master' ...<br>
224 commit: bf81b46</p></div><p>New remote-tracking branches will be stored under the shorthand name
225 that you gave "git remote add", in this case linux-nfs:</p><div class="literallayout"><p>$ git branch -r<br>
226 linux-nfs/master<br>
227 origin/master</p></div><p>If you run "git fetch <remote>" later, the remote-tracking branches for the
228 named <remote> will be updated.</p><p>If you examine the file .git/config, you will see that git has added
230 ...<br>
233 fetch = +refs/heads/*:refs/remotes/linux-nfs/*<br>
234 ...</p></div><p>This is what causes git to track the remote’s branches; you may modify
235 or delete these configuration options by editing .git/config with a
236 text editor. (See the "CONFIGURATION FILE" section of
237 <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.)</p></div></div><div class="chapter" title="Chapter 2. Exploring git history"><div class="titlepage"><div><div><h2 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring git history</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><p>Git is best thought of as a tool for storing the history of a
238 collection of files. It does this by storing compressed snapshots of
239 the contents of a file hierarchy, together with "commits" which show
240 the relationships between these snapshots.</p><p>Git provides extremely flexible and fast tools for exploring the
241 history of a project.</p><p>We start with one specialized tool that is useful for finding the
242 commit that introduced a bug into a project.</p><div class="section" title="How to use bisect to find a regression"><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
243 "master" crashes. Sometimes the best way to find the cause of such a
244 regression is to perform a brute-force search through the project’s
245 history to find the particular commit that caused the problem. The
246 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p><div class="literallayout"><p>$ git bisect start<br>
248 $ git bisect bad master<br>
250 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</p></div><p>If you run "git branch" at this point, you’ll see that git has
251 temporarily moved you in "(no branch)". HEAD is now detached from any
252 branch and points directly to a commit (with commit id 65934…) that
254 and see whether it crashes. Assume it does crash. Then:</p><div class="literallayout"><p>$ git bisect bad<br>
256 [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</p></div><p>checks out an older version. Continue like this, telling git at each
257 stage whether the version it gives you is good or bad, and notice
258 that the number of revisions left to test is cut approximately in
260 the guilty commit. You can then examine the commit with
261 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug
262 report with the commit id. Finally, run</p><div class="literallayout"><p>$ git bisect reset</p></div><p>to return you to the branch you were on before.</p><p>Note that the version which <code class="literal">git bisect</code> checks out for you at each
263 point is just a suggestion, and you’re free to try a different
264 version if you think it would be a good idea. For example,
265 occasionally you may land on a commit that broke something unrelated;
266 run</p><div class="literallayout"><p>$ git bisect visualize</p></div><p>which will run gitk and label the commit it chose with a marker that
267 says "bisect". Choose a safe-looking commit nearby, note its commit
268 id, and check it out with:</p><div class="literallayout"><p>$ git reset --hard fb47ddb2db...</p></div><p>then test, run "bisect good" or "bisect bad" as appropriate, and
270 fb47ddb2db…", you might just want to tell git that you want to skip
271 the current commit:</p><div class="literallayout"><p>$ git bisect skip</p></div><p>In this case, though, git may not eventually be able to tell the first
272 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
273 test script that can tell a good from a bad commit. See
274 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other "git
275 bisect" features.</p></div><div class="section" title="Naming commits"><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" type="disc"><li class="listitem">
276 40-hexdigit object name
278 branch name: refers to the commit at the head of the given
279 branch
281 tag name: refers to the commit pointed to by the given tag
282 (we’ve seen branches and tags are special cases of
283 <a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>).
285 HEAD: refers to the head of the current branch
287 <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> man page for the complete list of ways to
288 name revisions. Some examples:</p><div class="literallayout"><p>$ git show fb47ddb2 # the first few characters of the object name<br>
289 # are usually enough to specify it uniquely<br>
290 $ git show HEAD^ # the parent of the HEAD commit<br>
291 $ git show HEAD^^ # the grandparent<br>
292 $ git show HEAD~4 # the great-great-grandparent</p></div><p>Recall that merge commits may have more than one parent; by default,
293 ^ and ~ follow the first parent listed in the commit, but you can
294 also choose:</p><div class="literallayout"><p>$ git show HEAD^1 # show the first parent of HEAD<br>
295 $ git show HEAD^2 # show the second parent of HEAD</p></div><p>In addition to HEAD, there are several other special names for
296 commits:</p><p>Merges (to be discussed later), as well as operations such as
297 <code class="literal">git reset</code>, which change the currently checked-out commit, generally
298 set ORIG_HEAD to the value HEAD had before the current operation.</p><p>The <code class="literal">git fetch</code> operation always stores the head of the last fetched
300 specifying a local branch as the target of the operation</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git theirbranch</p></div><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,
301 which refers to the other branch that we’re merging in to the current
302 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
303 occasionally useful for translating some name for a commit to the object
305 e05db0fd4f31dde7005f075a84f96b360d05984b</p></div></div><div class="section" title="Creating tags"><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
306 running</p><div class="literallayout"><p>$ git tag stable-1 1b2e1d63ff</p></div><p>You can use stable-1 to refer to the commit 1b2e1d63ff.</p><p>This creates a "lightweight" tag. If you would also like to include a
307 comment with the tag, and possibly sign it cryptographically, then you
308 should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page
309 for details.</p></div><div class="section" title="Browsing revisions"><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
310 own, it shows all commits reachable from the parent commit; but you
311 can also make more specific requests:</p><div class="literallayout"><p>$ git log v2.5.. # commits since (not reachable from) v2.5<br>
312 $ git log test..master # commits reachable from master but not test<br>
313 $ git log master..test # ...reachable from test but not master<br>
314 $ git log master...test # ...reachable from either test or master,<br>
315 # but not both<br>
317 $ git log Makefile # commits which modify Makefile<br>
318 $ git log fs/ # ... which modify any file under fs/<br>
319 $ git log -S'foo()' # commits which add or remove any file data<br>
320 # matching the string 'foo()'</p></div><p>And of course you can combine all of these; the following finds
321 commits since v2.5 which touch the Makefile or any file under fs:</p><div class="literallayout"><p>$ git log v2.5.. Makefile fs/</p></div><p>You can also ask git log to show patches:</p><div class="literallayout"><p>$ git log -p</p></div><p>See the "--pretty" option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more
322 display options.</p><p>Note that git log starts with the most recent commit and works
323 backwards through the parents; however, since git history can contain
324 multiple independent lines of development, the particular order that
325 commits are listed in may be somewhat arbitrary.</p></div><div class="section" title="Generating diffs"><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
326 <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>:</p><div class="literallayout"><p>$ git diff master..test</p></div><p>That will produce the diff between the tips of the two branches. If
327 you’d prefer to find the diff from their common ancestor to test, you
328 can use three dots instead of two:</p><div class="literallayout"><p>$ git diff master...test</p></div><p>Sometimes what you want instead is a set of patches; for this you can
329 use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>:</p><div class="literallayout"><p>$ git format-patch master..test</p></div><p>will generate a file with a patch for each commit reachable from test
330 but not from master.</p></div><div class="section" title="Viewing old file versions"><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
331 correct revision first. But sometimes it is more convenient to be
332 able to view an old version of a single file without checking
333 anything out; this command does that:</p><div class="literallayout"><p>$ git show v2.5:fs/locks.c</p></div><p>Before the colon may be anything that names a commit, and after it
334 may be any path to a file tracked by git.</p></div><div class="section" title="Examples"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div><div class="section" title="Counting the number of commits on a branch"><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 "mybranch"
335 since it diverged from "origin":</p><div class="literallayout"><p>$ git log --pretty=oneline origin..mybranch | wc -l</p></div><p>Alternatively, you may often see this sort of thing done with the
336 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
337 of all the given commits:</p><div class="literallayout"><p>$ git rev-list origin..mybranch | wc -l</p></div></div><div class="section" title="Check whether two branches point at the same history"><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
338 in history.</p><div class="literallayout"><p>$ git diff origin..master</p></div><p>will tell you whether the contents of the project are the same at the
339 two branches; in theory, however, it’s possible that the same project
340 contents could have been arrived at by two different historical
341 routes. You could compare the object names:</p><div class="literallayout"><p>$ git rev-list origin<br>
342 e05db0fd4f31dde7005f075a84f96b360d05984b<br>
343 $ git rev-list master<br>
344 e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>Or you could recall that the … operator selects all commits
345 contained reachable from either one reference or the other but not
346 both: so</p><div class="literallayout"><p>$ git log origin...master</p></div><p>will return no commits when the two branches are equal.</p></div><div class="section" title="Find first tagged version including a given fix"><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.
347 You’d like to find the earliest tagged release that contains that
348 fix.</p><p>Of course, there may be more than one answer—if the history branched
349 after commit e05db0fd, then there could be multiple "earliest" tagged
350 releases.</p><p>You could just visually inspect the commits since e05db0fd:</p><div class="literallayout"><p>$ gitk e05db0fd..</p></div><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
351 name based on any tag it finds pointing to one of the commit’s
353 e05db0fd tags/v1.5.0-rc1^0~23</p></div><p>The <a class="ulink" href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the
354 revision using a tag on which the given commit is based:</p><div class="literallayout"><p>$ git describe e05db0fd<br>
355 v1.5.0-rc0-260-ge05db0f</p></div><p>but that may sometimes help you guess which tags might come after the
356 given commit.</p><p>If you just want to verify whether a given tagged version contains a
357 given commit, you could use <a class="ulink" href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p><div class="literallayout"><p>$ git merge-base e05db0fd v1.5.0-rc1<br>
358 e05db0fd4f31dde7005f075a84f96b360d05984b</p></div><p>The merge-base command finds a common ancestor of the given commits,
359 and always returns one or the other in the case where one is a
360 descendant of the other; so the above output shows that e05db0fd
361 actually is an ancestor of v1.5.0-rc1.</p><p>Alternatively, note that</p><div class="literallayout"><p>$ git log v1.5.0-rc1..e05db0fd</p></div><p>will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
362 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
363 the commits reachable from its arguments with a display on the left-hand
364 side that indicates which arguments that commit is reachable from. So,
365 you can run something like</p><div class="literallayout"><p>$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2<br>
366 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br>
367 available<br>
371 ...</p></div><p>then search for a line that looks like</p><div class="literallayout"><p>+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if<br>
373 from v1.5.0-rc2, but not from v1.5.0-rc0.</p></div><div class="section" title="Showing commits unique to a given branch"><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
374 head named "master" but not from any other head in your repository.</p><p>We can list all the heads in this repository with
375 <a class="ulink" href="git-show-ref.html" target="_top">git-show-ref(1)</a>:</p><div class="literallayout"><p>$ git show-ref --heads<br>
376 bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial<br>
377 db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint<br>
378 a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master<br>
380 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes</p></div><p>We can get just the branch-head names, and remove "master", with
381 the help of the standard utilities cut and grep:</p><div class="literallayout"><p>$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'<br>
382 refs/heads/core-tutorial<br>
383 refs/heads/maint<br>
385 refs/heads/tutorial-fixes</p></div><p>And then we can ask to see all the commits reachable from master
386 but not from these other heads:</p><div class="literallayout"><p>$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |<br>
387 grep -v '^refs/heads/master' )</p></div><p>Obviously, endless variations are possible; for example, to see all
388 commits reachable from some head but not from any tag in the repository:</p><div class="literallayout"><p>$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )</p></div><p>(See <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for explanations of commit-selecting
389 syntax such as <code class="literal">--not</code>.)</p></div><div class="section" title="Creating a changelog and tarball for a software release"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div><p>The <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from
390 any version of a project; for example:</p><div class="literallayout"><p>$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz</p></div><p>will use HEAD to produce a tar archive in which each filename is
391 preceded by "project/".</p><p>If you’re releasing a new version of a software project, you may want
392 to simultaneously make a changelog to include in the release
393 announcement.</p><p>Linus Torvalds, for example, makes new kernel releases by tagging them,
394 then running:</p><div class="literallayout"><p>$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7</p></div><p>where release-script is a shell script that looks like:</p><div class="literallayout"><p>#!/bin/sh<br>
403 echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"</p></div><p>and then he just cut-and-pastes the output commands after verifying that
404 they look OK.</p></div><div class="section" title="Finding commits referencing a file with given content"><div class="titlepage"><div><div><h3 class="title"><a name="Finding-commits-With-given-Content"></a>Finding commits referencing a file with given content</h3></div></div></div><p>Somebody hands you a copy of a file, and asks which commits modified a
405 file such that it contained the given content either before or after the
406 commit. You can find out with this:</p><div class="literallayout"><p>$ git log --raw --abbrev=40 --pretty=oneline |<br>
407 grep -B 1 `git hash-object filename`</p></div><p>Figuring out why this works is left as an exercise to the (advanced)
408 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
409 <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" title="Chapter 3. Developing with git"><div class="titlepage"><div><div><h2 class="title"><a name="Developing-With-git"></a>Chapter 3. Developing with git</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><div class="section" title="Telling git your name"><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
410 easiest way to do so is to make sure the following lines appear in a
412 name = Your Name Comes Here<br>
413 email = you@yourdomain.example.com</p></div><p>(See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
414 details on the configuration file.)</p></div><div class="section" title="Creating a new repository"><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><div class="literallayout"><p>$ mkdir project<br>
415 $ cd project<br>
416 $ git init</p></div><p>If you have some initial content (say, a tarball):</p><div class="literallayout"><p>$ tar xzvf project.tar.gz<br>
417 $ cd project<br>
418 $ git init<br>
419 $ git add . # include everything below ./ in the first commit:<br>
420 $ git commit</p></div></div><div class="section" title="How to make a commit"><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">
421 Making some changes to the working directory using your
422 favorite editor.
424 Telling git about your changes.
426 Creating the commit using the content you told git about
427 in step 2.
429 times as you want: in order to keep track of what you want committed
430 at step 3, git maintains a snapshot of the tree’s contents in a
431 special staging area called "the index."</p><p>At the beginning, the content of the index will be identical to
432 that of the HEAD. The command "git diff --cached", which shows
433 the difference between the HEAD and the index, should therefore
434 produce no output at that point.</p><p>Modifying the index is easy:</p><p>To update the index with the new contents of a modified file, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To add the contents of a new file to the index, use</p><div class="literallayout"><p>$ git add path/to/file</p></div><p>To remove a file from the index and from the working tree,</p><div class="literallayout"><p>$ git rm path/to/file</p></div><p>After each step you can verify that</p><div class="literallayout"><p>$ git diff --cached</p></div><p>always shows the difference between the HEAD and the index file—this
435 is what you’d commit if you created the commit now—and that</p><div class="literallayout"><p>$ git diff</p></div><p>shows the difference between the working tree and the index file.</p><p>Note that "git add" always adds just the current contents of a file
436 to the index; further changes to the same file will be ignored unless
437 you run <code class="literal">git add</code> on the file again.</p><p>When you’re ready, just run</p><div class="literallayout"><p>$ git commit</p></div><p>and git will prompt you for a commit message and then create the new
438 commit. Check to make sure it looks like what you expected with</p><div class="literallayout"><p>$ git show</p></div><p>As a special shortcut,</p><div class="literallayout"><p>$ git commit -a</p></div><p>will update the index with any files that you’ve modified or removed
439 and create a commit, all in one step.</p><p>A number of commands are useful for keeping track of what you’re
440 about to commit:</p><div class="literallayout"><p>$ git diff --cached # difference between HEAD and the index; what<br>
442 $ git diff # difference between the index file and your<br>
443 # working directory; changes that would not<br>
445 $ git diff HEAD # difference between HEAD and working tree; what<br>
447 $ git status # a brief per-file summary of the above.</p></div><p>You can also use <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> to create commits, view changes in
448 the index and the working tree files, and individually select diff hunks
449 for inclusion in the index (by right-clicking on the diff hunk and
450 choosing "Stage Hunk For Commit").</p></div><div class="section" title="Creating good commit messages"><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
451 with a single short (less than 50 character) line summarizing the
452 change, followed by a blank line and then a more thorough
453 description. Tools that turn commits into email, for example, use
454 the first line on the Subject line and the rest of the commit in the
455 body.</p></div><div class="section" title="Ignoring files"><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.
456 This typically includes files generated by a build process or temporary
457 backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with git
458 is just a matter of <span class="emphasis"><em>not</em></span> calling <code class="literal">git add</code> on them. But it quickly becomes
459 annoying to have these untracked files lying around; e.g. they make
460 <code class="literal">git add .</code> practically useless, and they keep showing up in the output of
461 <code class="literal">git status</code>.</p><p>You can tell git to ignore certain files by creating a file called .gitignore
462 in the top level of your working directory, with contents such as:</p><div class="literallayout"><p># Lines starting with '#' are considered comments.<br>
463 # Ignore any file named foo.txt.<br>
464 foo.txt<br>
465 # Ignore (generated) html files,<br>
466 *.html<br>
467 # except foo.html which is maintained by hand.<br>
468 !foo.html<br>
469 # Ignore objects and archives.<br>
470 *.[oa]</p></div><p>See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for a detailed explanation of the syntax. You can
471 also place .gitignore files in other directories in your working tree, and they
472 will apply to those directories and their subdirectories. The <code class="literal">.gitignore</code>
473 files can be added to your repository like any other files (just run <code class="literal">git add
474 .gitignore</code> and <code class="literal">git commit</code>, as usual), which is convenient when the exclude
475 patterns (such as patterns matching build output files) would also make sense
476 for other users who clone your repository.</p><p>If you wish the exclude patterns to affect only certain repositories
477 (instead of every repository for a given project), you may instead put
478 them in a file in your repository named .git/info/exclude, or in any file
479 specified by the <code class="literal">core.excludesfile</code> configuration variable. Some git
480 commands can also take exclude patterns directly on the command line.
481 See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for the details.</p></div><div class="section" title="How to merge"><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
482 <a class="ulink" href="git-merge.html" target="_top">git-merge(1)</a>:</p><div class="literallayout"><p>$ git merge branchname</p></div><p>merges the development in the branch "branchname" into the current
484 changes made up to the latest commit in your current branch since
485 their histories forked. The work tree is overwritten by the result of
486 the merge when this combining is done cleanly, or overwritten by a
487 half-merged results when this combining results in conflicts.
488 Therefore, if you have uncommitted changes touching the same files as
489 the ones impacted by the merge, Git will refuse to proceed. Most of
490 the time, you will want to commit your changes before you can merge,
491 and if you don’t, then <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> can take these changes
492 away while you’re doing the merge, and reapply them afterwards.</p><p>If the changes are independent enough, Git will automatically complete
493 the merge and commit the result (or reuse an existing commit in case
494 of <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>, see below). On the other hand,
495 if there are conflicts—for example, if the same file is
496 modified in two different ways in the remote branch and the local
497 branch—then you are warned; the output may look something like this:</p><div class="literallayout"><p>$ git merge next<br>
499 Auto-merged file.txt<br>
500 CONFLICT (content): Merge conflict in file.txt<br>
501 Automatic merge failed; fix conflicts and then commit the result.</p></div><p>Conflict markers are left in the problematic files, and after
502 you resolve the conflicts manually, you can update the index
503 with the contents and run git commit, as you normally would when
504 creating a new file.</p><p>If you examine the resulting commit using gitk, you will see that it
505 has two parents, one pointing to the top of the current branch, and
506 one to the top of the other branch.</p></div><div class="section" title="Resolving a merge"><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
507 the working tree in a special state that gives you all the
508 information you need to help resolve the merge.</p><p>Files with conflicts are marked specially in the index, so until you
509 resolve the problem and update the index, <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> will
511 file.txt: needs merge</p></div><p>Also, <a class="ulink" href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the
512 files with conflicts will have conflict markers added, like this:</p><div class="literallayout"><p><<<<<<< HEAD:file.txt<br>
513 Hello world<br>
514 =======<br>
515 Goodbye<br>
516 >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>All you need to do is edit the files to resolve the conflicts, and then</p><div class="literallayout"><p>$ git add file.txt<br>
517 $ git commit</p></div><p>Note that the commit message will already be filled in for you with
518 some information about the merge. Normally you can just use this
519 default message unchanged, but you may add additional commentary of
520 your own if desired.</p><p>The above is all you need to know to resolve a simple merge. But git
521 also provides more information to help resolve conflicts:</p><div class="section" title="Getting conflict-resolution help during a merge"><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
522 already added to the index file, so <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> shows only
524 diff --cc file.txt<br>
526 --- a/file.txt<br>
527 +++ b/file.txt<br>
530 +Hello world<br>
531 ++=======<br>
532 + Goodbye<br>
533 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt</p></div><p>Recall that the commit which will be committed after we resolve this
534 conflict will have two parents instead of the usual one: one parent
535 will be HEAD, the tip of the current branch; the other will be the
536 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
537 these three "file stages" represents a different version of the file:</p><div class="literallayout"><p>$ git show :1:file.txt # the file in a common ancestor of both branches<br>
539 $ git show :3:file.txt # the version from MERGE_HEAD.</p></div><p>When you ask <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the conflicts, it runs a
540 three-way diff between the conflicted merge results in the work tree with
542 mixed (in other words, when a hunk’s merge results come only from stage 2,
543 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
546 column is used for differences between the first parent and the working
547 directory copy, and the second for differences between the second parent
548 and the working directory copy. (See the "COMBINED DIFF FORMAT" section
549 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
551 diff --cc file.txt<br>
553 --- a/file.txt<br>
554 +++ b/file.txt<br>
556 - Hello world<br>
557 -Goodbye<br>
559 first parent, deleted "Goodbye" from the second parent, and added
560 "Goodbye world", which was previously absent from both.</p><p>Some special diff options allow diffing the working directory against
561 any of these stages:</p><div class="literallayout"><p>$ git diff -1 file.txt # diff against stage 1<br>
562 $ git diff --base file.txt # same as the above<br>
564 $ git diff --ours file.txt # same as the above<br>
566 $ git diff --theirs file.txt # same as the above.</p></div><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
568 $ gitk --merge</p></div><p>These will display all commits which exist only on HEAD or on
569 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
570 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><div class="literallayout"><p>$ git add file.txt</p></div><p>the different stages of that file will be "collapsed", after which
571 <code class="literal">git diff</code> will (by default) no longer show diffs for that file.</p></div></div><div class="section" title="Undoing a merge"><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
572 away, you can always return to the pre-merge state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>Or, if you’ve already committed the merge that you want to throw away,</p><div class="literallayout"><p>$ git reset --hard ORIG_HEAD</p></div><p>However, this last command can be dangerous in some cases—never
573 throw away a commit you have already committed if that commit may
574 itself have been merged into another branch, as doing so may confuse
575 further merges.</p></div><div class="section" title="Fast-forward merges"><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
576 differently. Normally, a merge results in a merge commit, with two
577 parents, one pointing at each of the two lines of development that
578 were merged.</p><p>However, if the current branch is a descendant of the other—so every
579 commit present in the one is already contained in the other—then git
580 just performs a "fast-forward"; the head of the current branch is moved
581 forward to point at the head of the merged-in branch, without any new
582 commits being created.</p></div><div class="section" title="Fixing mistakes"><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
583 mistake, you can return the entire working tree to the last committed
584 state with</p><div class="literallayout"><p>$ git reset --hard HEAD</p></div><p>If you make a commit that you later wish you hadn’t, there are two
585 fundamentally different ways to fix the problem:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
586 You can create a new commit that undoes whatever was done
587 by the old commit. This is the correct thing if your
588 mistake has already been made public.
590 You can go back and modify the old commit. You should
591 never do this if you have already made the history public;
592 git does not normally expect the "history" of a project to
593 change, and cannot correctly perform repeated merges from
594 a branch that has had its history changed.
595 </li></ol></div><div class="section" title="Fixing a mistake with a new commit"><div class="titlepage"><div><div><h3 class="title"><a name="reverting-a-commit"></a>Fixing a mistake with a new commit</h3></div></div></div><p>Creating a new commit that reverts an earlier change is very easy;
596 just pass the <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad
597 commit; for example, to revert the most recent commit:</p><div class="literallayout"><p>$ git revert HEAD</p></div><p>This will create a new commit which undoes the change in HEAD. You
598 will be given a chance to edit the commit message for the new commit.</p><p>You can also revert an earlier change, for example, the next-to-last:</p><div class="literallayout"><p>$ git revert HEAD^</p></div><p>In this case git will attempt to undo the old change while leaving
599 intact any changes made since then. If more recent changes overlap
600 with the changes to be reverted, then you will be asked to fix
601 conflicts manually, just as in the case of <a class="link" href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p></div><div class="section" title="Fixing a mistake by rewriting history"><div class="titlepage"><div><div><h3 class="title"><a name="fixing-a-mistake-by-rewriting-history"></a>Fixing a mistake by rewriting history</h3></div></div></div><p>If the problematic commit is the most recent commit, and you have not
602 yet made that commit public, then you may just
603 <a class="link" href="#undoing-a-merge" title="Undoing a merge">destroy it using <code class="literal">git reset</code></a>.</p><p>Alternatively, you
604 can edit the working directory and update the index to fix your
605 mistake, just as if you were going to <a class="link" href="#how-to-make-a-commit" title="How to make a commit">create a new commit</a>, then run</p><div class="literallayout"><p>$ git commit --amend</p></div><p>which will replace the old commit by a new commit incorporating your
606 changes, giving you a chance to edit the old commit message first.</p><p>Again, you should never do this to a commit that may already have
607 been merged into another branch; use <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> instead in
608 that case.</p><p>It is also possible to replace commits further back in the history, but
609 this is an advanced topic to be left for
610 <a class="link" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">another chapter</a>.</p></div><div class="section" title="Checking out an old version of a file"><div class="titlepage"><div><div><h3 class="title"><a name="checkout-of-path"></a>Checking out an old version of a file</h3></div></div></div><p>In the process of undoing a previous bad change, you may find it
611 useful to check out an older version of a particular file using
612 <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>. We’ve used <code class="literal">git checkout</code> before to switch
613 branches, but it has quite different behavior if it is given a path
614 name: the command</p><div class="literallayout"><p>$ git checkout HEAD^ path/to/file</p></div><p>replaces path/to/file by the contents it had in the commit HEAD^, and
615 also updates the index to match. It does not change branches.</p><p>If you just want to look at an old version of the file, without
616 modifying the working directory, you can do that with
617 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>:</p><div class="literallayout"><p>$ git show HEAD^:path/to/file</p></div><p>which will display the given version of the file.</p></div><div class="section" title="Temporarily setting aside work in progress"><div class="titlepage"><div><div><h3 class="title"><a name="interrupted-work"></a>Temporarily setting aside work in progress</h3></div></div></div><p>While you are in the middle of working on something complicated, you
618 find an unrelated but obvious and trivial bug. You would like to fix it
619 before continuing. You can use <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> to save the current
620 state of your work, and after fixing the bug (or, optionally after doing
621 so on a different branch and then coming back), unstash the
622 work-in-progress changes.</p><div class="literallayout"><p>$ git stash save "work in progress for foo feature"</p></div><p>This command will save your changes away to the <code class="literal">stash</code>, and
623 reset your working tree and the index to match the tip of your
624 current branch. Then you can make your fix as usual.</p><div class="literallayout"><p>... edit and test ...<br>
625 $ git commit -a -m "blorpl: typofix"</p></div><p>After that, you can go back to what you were working on with
626 <code class="literal">git stash pop</code>:</p><div class="literallayout"><p>$ git stash pop</p></div></div></div><div class="section" title="Ensuring good performance"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-good-performance"></a>Ensuring good performance</h2></div></div></div><p>On large repositories, git depends on compression to keep the history
627 information from taking up too much space on disk or in memory.</p><p>This compression is not performed automatically. Therefore you
628 should occasionally run <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a>:</p><div class="literallayout"><p>$ git gc</p></div><p>to recompress the archive. This can be very time-consuming, so
629 you may prefer to run <code class="literal">git gc</code> when you are not doing other work.</p></div><div class="section" title="Ensuring reliability"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-reliability"></a>Ensuring reliability</h2></div></div></div><div class="section" title="Checking the repository for corruption"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-corruption"></a>Checking the repository for corruption</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks
630 on the repository, and reports on any problems. This may take some
631 time. The most common warning by far is about "dangling" objects:</p><div class="literallayout"><p>$ git fsck<br>
636 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f<br>
638 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085<br>
639 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f<br>
640 ...</p></div><p>Dangling objects are not a problem. At worst they may take up a little
641 extra disk space. They can sometimes provide a last-resort method for
642 recovering lost work—see <a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for details.</p></div><div class="section" title="Recovering lost changes"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-lost-changes"></a>Recovering lost changes</h3></div></div></div><div class="section" title="Reflogs"><div class="titlepage"><div><div><h4 class="title"><a name="reflogs"></a>Reflogs</h4></div></div></div><p>Say you modify a branch with <code class="literal"><a class="ulink" href="git-reset.html" target="_top">git-reset(1)</a> --hard</code>, and then
643 realize that the branch was the only reference you had to that point in
645 previous values of each branch. So in this case you can still find the
646 old history using, for example,</p><div class="literallayout"><p>$ git log master@{1}</p></div><p>This lists the commits reachable from the previous version of the
647 "master" branch head. This syntax can be used with any git command
648 that accepts a commit, not just with git log. Some other examples:</p><div class="literallayout"><p>$ git show master@{2} # See where the branch pointed 2,<br>
650 $ gitk master@{yesterday} # See where it pointed yesterday,<br>
652 $ git log --walk-reflogs master # show reflog entries for master</p></div><p>A separate reflog is kept for the HEAD, so</p><div class="literallayout"><p>$ git show HEAD@{"1 week ago"}</p></div><p>will show what HEAD pointed to one week ago, not what the current branch
653 pointed to one week ago. This allows you to see the history of what
655 pruned. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> and <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> to learn
656 how to control this pruning, and see the "SPECIFYING REVISIONS"
657 section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for details.</p><p>Note that the reflog history is very different from normal git history.
658 While normal history is shared by every repository that works on the
659 same project, the reflog history is not shared: it tells you only about
660 how the branches in your local repository have changed over time.</p></div><div class="section" title="Examining dangling objects"><div class="titlepage"><div><div><h4 class="title"><a name="dangling-object-recovery"></a>Examining dangling objects</h4></div></div></div><p>In some situations the reflog may not be able to save you. For example,
661 suppose you delete a branch, then realize you need the history it
662 contained. The reflog is also deleted; however, if you have not yet
663 pruned the repository, then you may still be able to find the lost
665 <a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for the details.</p><div class="literallayout"><p>$ git fsck<br>
669 ...</p></div><p>You can examine
670 one of those dangling commits with, for example,</p><div class="literallayout"><p>$ gitk 7281251ddd --not --all</p></div><p>which does what it sounds like: it says that you want to see the commit
671 history that is described by the dangling commit(s), but not the
672 history that is described by all your existing branches and tags. Thus
673 you get exactly the history reachable from that commit that is lost.
674 (And notice that it might not be just one commit: we only report the
675 "tip of the line" as being dangling, but there might be a whole deep
676 and complex commit history that was dropped.)</p><p>If you decide you want the history back, you can always create a new
677 reference pointing to it, for example, a new branch:</p><div class="literallayout"><p>$ git branch recovered-branch 7281251ddd</p></div><p>Other types of dangling objects (blobs and trees) are also possible, and
678 dangling objects can arise in other situations.</p></div></div></div></div><div class="chapter" title="Chapter 4. Sharing development with others"><div class="titlepage"><div><div><h2 class="title"><a name="sharing-development"></a>Chapter 4. Sharing development with others</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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="#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></div><div class="section" title="Getting updates with git pull"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="getting-updates-With-git-pull"></a>Getting updates with git pull</h2></div></div></div><p>After you clone a repository and commit a few changes of your own, you
679 may wish to check the original repository for updates and merge them
680 into your own work.</p><p>We have already seen <a class="link" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">how to keep remote-tracking branches up to date</a> with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>,
681 and how to merge two branches. So you can merge in changes from the
683 $ git merge origin/master</p></div><p>However, the <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in
684 one step:</p><div class="literallayout"><p>$ git pull origin master</p></div><p>In fact, if you have "master" checked out, then this branch has been
685 configured by "git clone" to get changes from the HEAD branch of the
686 origin repository. So often you can
687 accomplish the above with just a simple</p><div class="literallayout"><p>$ git pull</p></div><p>This command will fetch changes from the remote branches to your
688 remote-tracking branches <code class="literal">origin/*</code>, and merge the default branch into
689 the current branch.</p><p>More generally, a branch that is created from a remote-tracking branch
690 will pull
691 by default from that branch. See the descriptions of the
693 <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>, and the discussion of the <code class="literal">--track</code> option in
694 <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>, to learn how to control these defaults.</p><p>In addition to saving you keystrokes, "git pull" also helps you by
695 producing a default commit message documenting the branch and
696 repository that you pulled from.</p><p>(But note that no such commit will be created in the case of a
697 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; instead, your branch will just be
698 updated to point to the latest commit from the upstream branch.)</p><p>The <code class="literal">git pull</code> command can also be given "." as the "remote" repository,
699 in which case it just merges in a branch from the current repository; so
701 $ git merge branch</p></div><p>are roughly equivalent. The former is actually very commonly used.</p></div><div class="section" title="Submitting patches to a project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="submitting-patches"></a>Submitting patches to a project</h2></div></div></div><p>If you just have a few changes, the simplest way to submit them may
702 just be to send them as patches in email:</p><p>First, use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>; for example:</p><div class="literallayout"><p>$ git format-patch origin</p></div><p>will produce a numbered series of files in the current directory, one
703 for each patch in the current branch but not in origin/HEAD.</p><p>You can then import these into your mail client and send them by
704 hand. However, if you have a lot to send at once, you may prefer to
705 use the <a class="ulink" href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process.
706 Consult the mailing list for your project first to determine how they
707 prefer such patches be handled.</p></div><div class="section" title="Importing patches to a project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="importing-patches"></a>Importing patches to a project</h2></div></div></div><p>Git also provides a tool called <a class="ulink" href="git-am.html" target="_top">git-am(1)</a> (am stands for
708 "apply mailbox"), for importing such an emailed series of patches.
709 Just save all of the patch-containing messages, in order, into a
710 single mailbox file, say "patches.mbox", then run</p><div class="literallayout"><p>$ git am -3 patches.mbox</p></div><p>Git will apply each patch in order; if any conflicts are found, it
711 will stop, and you can fix the conflicts as described in
712 "<a class="link" href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The "-3" option tells
713 git to perform a merge; if you would prefer it just to abort and
714 leave your tree and index untouched, you may omit that option.)</p><p>Once the index is updated with the results of the conflict
715 resolution, instead of creating a new commit, just run</p><div class="literallayout"><p>$ git am --resolved</p></div><p>and git will create the commit for you and continue applying the
716 remaining patches from the mailbox.</p><p>The final result will be a series of commits, one for each patch in
717 the original mailbox, with authorship and commit log message each
718 taken from the message containing each patch.</p></div><div class="section" title="Public git repositories"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="public-repositories"></a>Public git repositories</h2></div></div></div><p>Another way to submit changes to a project is to tell the maintainer
719 of that project to pull the changes from your repository using
720 <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>. In the section "<a class="link" href="#getting-updates-With-git-pull" title="Getting updates with git pull">Getting updates with <code class="literal">git pull</code></a>" we described this as a way to get
721 updates from the "main" repository, but it works just as well in the
722 other direction.</p><p>If you and the maintainer both have accounts on the same machine, then
723 you can just pull changes from each other’s repositories directly;
724 commands that accept repository URLs as arguments will also accept a
726 $ git pull /path/to/other/repository</p></div><p>or an ssh URL:</p><div class="literallayout"><p>$ git clone ssh://yourhost/~you/repository</p></div><p>For projects with few developers, or for synchronizing a few private
727 repositories, this may be all you need.</p><p>However, the more common way to do this is to maintain a separate public
728 repository (usually on a different host) for others to pull changes
729 from. This is usually more convenient, and allows you to cleanly
730 separate private work in progress from publicly visible work.</p><p>You will continue to do your day-to-day work in your personal
731 repository, but periodically "push" changes from your personal
732 repository into your public repository, allowing other developers to
733 pull from that repository. So the flow of changes, in a situation
734 where there is one other developer with a public repository, looks
736 your personal repo ------------------> your public repo
737 ^ |
738 | |
739 | you pull | they pull
740 | |
741 | |
742 | they push V
743 their public repo <------------------- their repo</pre><p>We explain how to do this in the following sections.</p><div class="section" title="Setting up a public repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-public-repository"></a>Setting up a public repository</h3></div></div></div><p>Assume your personal repository is in the directory ~/proj. We
744 first create a new clone of the repository and tell <code class="literal">git daemon</code> that it
746 $ touch proj.git/git-daemon-export-ok</p></div><p>The resulting directory proj.git contains a "bare" git repository—it is
747 just the contents of the ".git" directory, without any files checked out
748 around it.</p><p>Next, copy proj.git to the server where you plan to host the
749 public repository. You can use scp, rsync, or whatever is most
750 convenient.</p></div><div class="section" title="Exporting a git repository via the git protocol"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-git"></a>Exporting a git repository via the git protocol</h3></div></div></div><p>This is the preferred method.</p><p>If someone else administers the server, they should tell you what
751 directory to put the repository in, and what git:// URL it will appear
752 at. You can then skip to the section
753 "<a class="link" href="#pushing-changes-to-a-public-repository" title="Pushing changes to a public repository">Pushing changes to a public repository</a>", below.</p><p>Otherwise, all you need to do is start <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a>; it will
754 listen on port 9418. By default, it will allow access to any directory
755 that looks like a git directory and contains the magic file
757 arguments will further restrict the exports to those paths.</p><p>You can also run <code class="literal">git daemon</code> as an inetd service; see the
758 <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a> man page for details. (See especially the
759 examples section.)</p></div><div class="section" title="Exporting a git repository via http"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-http"></a>Exporting a git repository via http</h3></div></div></div><p>The git protocol gives better performance and reliability, but on a
760 host with a web server set up, http exports may be simpler to set up.</p><p>All you need to do is place the newly created bare git repository in
761 a directory that is exported by the web server, and make some
762 adjustments to give web clients some extra information they need:</p><div class="literallayout"><p>$ mv proj.git /home/you/public_html/proj.git<br>
763 $ cd proj.git<br>
764 $ git --bare update-server-info<br>
765 $ mv hooks/post-update.sample hooks/post-update</p></div><p>(For an explanation of the last two lines, see
766 <a class="ulink" href="git-update-server-info.html" target="_top">git-update-server-info(1)</a> and <a class="ulink" href="githooks.html" target="_top">githooks(5)</a>.)</p><p>Advertise the URL of proj.git. Anybody else should then be able to
767 clone or pull from that URL, for example with a command line like:</p><div class="literallayout"><p>$ git clone http://yourserver.com/~you/proj.git</p></div><p>(See also
768 <a class="ulink" href="howto/setup-git-server-over-http.txt" target="_top">setup-git-server-over-http</a>
769 for a slightly more sophisticated setup using WebDAV which also
770 allows pushing over http.)</p></div><div class="section" title="Pushing changes to a public repository"><div class="titlepage"><div><div><h3 class="title"><a name="pushing-changes-to-a-public-repository"></a>Pushing changes to a public repository</h3></div></div></div><p>Note that the two techniques outlined above (exporting via
771 <a class="link" href="#exporting-via-http" title="Exporting a git repository via http">http</a> or <a class="link" href="#exporting-via-git" title="Exporting a git repository via the git protocol">git</a>) allow other
772 maintainers to fetch your latest changes, but they do not allow write
773 access, which you will need to update the public repository with the
774 latest changes created in your private repository.</p><p>The simplest way to do this is using <a class="ulink" href="git-push.html" target="_top">git-push(1)</a> and ssh; to
775 update the remote branch named "master" with the latest state of your
776 branch named "master", run</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master:master</p></div><p>or just</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git master</p></div><p>As with <code class="literal">git fetch</code>, <code class="literal">git push</code> will complain if this does not result in a
777 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; see the following section for details on
780 repository that has a checked-out working tree, but the working tree
781 will not be updated by the push. This may lead to unexpected results if
782 the branch you push to is the currently checked-out branch!</p><p>As with <code class="literal">git fetch</code>, you may also set up configuration options to
783 save typing; so, for example, after</p><div class="literallayout"><p>$ cat >>.git/config <<EOF<br>
785 url = ssh://yourserver.com/~you/proj.git<br>
786 EOF</p></div><p>you should be able to perform the above push with just</p><div class="literallayout"><p>$ git push public-repo master</p></div><p>See the explanations of the remote.<name>.url, branch.<name>.remote,
787 and remote.<name>.push options in <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
788 details.</p></div><div class="section" title="What to do when a push fails"><div class="titlepage"><div><div><h3 class="title"><a name="forcing-push"></a>What to do when a push fails</h3></div></div></div><p>If a push would not result in a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> of the
789 remote branch, then it will fail with an error like:</p><div class="literallayout"><p>error: remote 'refs/heads/master' is not an ancestor of<br>
790 local 'refs/heads/master'.<br>
791 Maybe you are not up-to-date and need to pull first?<br>
792 error: failed to push to 'ssh://yourserver.com/~you/proj.git'</p></div><p>This can happen, for example, if you:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
796 (as in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a>), or
799 in <a class="xref" href="#using-git-rebase" title="Keeping a patch series up to date using git rebase">the section called “Keeping a patch series up to date using git rebase”</a>).
800 </li></ul></div><p>You may force <code class="literal">git push</code> to perform the update anyway by preceding the
801 branch name with a plus sign:</p><div class="literallayout"><p>$ git push ssh://yourserver.com/~you/proj.git +master</p></div><p>Normally whenever a branch head in a public repository is modified, it
802 is modified to point to a descendant of the commit that it pointed to
803 before. By forcing a push in this situation, you break that convention.
804 (See <a class="xref" href="#problems-With-rewriting-history" title="Problems with rewriting history">the section called “Problems with rewriting history”</a>.)</p><p>Nevertheless, this is a common practice for people that need a simple
805 way to publish a work-in-progress patch series, and it is an acceptable
806 compromise as long as you warn other developers that this is how you
807 intend to manage the branch.</p><p>It’s also possible for a push to fail in this way when other people have
808 the right to push to the same repository. In that case, the correct
809 solution is to retry the push after first updating your work: either by a
810 pull, or by a fetch followed by a rebase; see the
811 <a class="link" href="#setting-up-a-shared-repository" title="Setting up a shared repository">next section</a> and
812 <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for more.</p></div><div class="section" title="Setting up a shared repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-a-shared-repository"></a>Setting up a shared repository</h3></div></div></div><p>Another way to collaborate is by using a model similar to that
813 commonly used in CVS, where several developers with special rights
814 all push to and pull from a single shared repository. See
815 <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for instructions on how to
816 set this up.</p><p>However, while there is nothing wrong with git’s support for shared
817 repositories, this mode of operation is not generally recommended,
818 simply because the mode of collaboration that git supports—by
819 exchanging patches and pulling from public repositories—has so many
820 advantages over the central shared repository:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
821 Git’s ability to quickly import and merge patches allows a
822 single maintainer to process incoming changes even at very
824 an easy way for that maintainer to delegate this job to other
825 maintainers while still allowing optional review of incoming
826 changes.
828 Since every developer’s repository has the same complete copy
829 of the project history, no repository is special, and it is
830 trivial for another developer to take over maintenance of a
831 project, either by mutual agreement, or because a maintainer
832 becomes unresponsive or difficult to work with.
834 The lack of a central group of "committers" means there is
835 less need for formal decisions about who is "in" and who is
836 "out".
837 </li></ul></div></div><div class="section" title="Allowing web browsing of a repository"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-gitweb"></a>Allowing web browsing of a repository</h3></div></div></div><p>The gitweb cgi script provides users an easy way to browse your
838 project’s files and history without having to install git; see the file
839 gitweb/INSTALL in the git source tree for instructions on setting it up.</p></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-development-examples"></a>Examples</h2></div></div></div><div class="section" title="Maintaining topic branches for a Linux subsystem maintainer"><div class="titlepage"><div><div><h3 class="title"><a name="maintaining-topic-branches"></a>Maintaining topic branches for a Linux subsystem maintainer</h3></div></div></div><p>This describes how Tony Luck uses git in his role as maintainer of the
840 IA64 architecture for the Linux kernel.</p><p>He uses two public branches:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
841 A "test" tree into which patches are initially placed so that they
842 can get some exposure when integrated with other ongoing development.
843 This tree is available to Andrew for pulling into -mm whenever he
844 wants.
846 A "release" tree into which tested patches are moved for final sanity
847 checking, and as a vehicle to send them upstream to Linus (by sending
848 him a "please pull" request.)
850 containing a logical grouping of patches.</p><p>To set this up, first create your work tree by cloning Linus’s public
851 tree:</p><div class="literallayout"><p>$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work<br>
852 $ cd work</p></div><p>Linus’s tree will be stored in the remote-tracking branch named origin/master,
853 and can be updated using <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>; you can track other
854 public trees using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a> to set up a "remote" and
855 <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> to keep them up-to-date; see
856 <a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a>.</p><p>Now create the branches in which you are going to work; these start out
857 at the current tip of origin/master branch, and should be set up (using
858 the --track option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>) to merge changes in from
860 $ git branch --track release origin/master</p></div><p>These can be easily kept up to date using <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.</p><div class="literallayout"><p>$ git checkout test && git pull<br>
861 $ git checkout release && git pull</p></div><p>Important note! If you have any local changes in these branches, then
862 this merge will create a commit object in the history (with no local
863 changes git will simply do a "fast-forward" merge). Many people dislike
864 the "noise" that this creates in the Linux history, so you should avoid
865 doing this capriciously in the "release" branch, as these noisy commits
866 will become part of the permanent history when you ask Linus to pull
867 from the release branch.</p><p>A few configuration variables (see <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>) can
868 make it easy to push both branches to your public tree. (See
869 <a class="xref" href="#setting-up-a-public-repository" title="Setting up a public repository">the section called “Setting up a public repository”</a>.)</p><div class="literallayout"><p>$ cat >> .git/config <<EOF<br>
872 push = release<br>
873 push = test<br>
874 EOF</p></div><p>Then you can push both the test and release trees using
875 <a class="ulink" href="git-push.html" target="_top">git-push(1)</a>:</p><div class="literallayout"><p>$ git push mytree</p></div><p>or push just one of the test and release branches using:</p><div class="literallayout"><p>$ git push mytree test</p></div><p>or</p><div class="literallayout"><p>$ git push mytree release</p></div><p>Now to apply some patches from the community. Think of a short
876 snappy name for a branch to hold this patch (or related group of
877 patches), and create a new branch from a recent stable tag of
878 Linus’s branch. Picking a stable base for your branch will:
879 1) help you: by avoiding inclusion of unrelated and perhaps lightly
880 tested changes
881 2) help future bug hunters that use "git bisect" to find problems</p><div class="literallayout"><p>$ git checkout -b speed-up-spinlocks v2.6.35</p></div><p>Now you apply the patch(es), run some tests, and commit the change(s). If
882 the patch is a multi-part series, then you should apply each as a separate
883 commit to this branch.</p><div class="literallayout"><p>$ ... patch ... test ... commit [ ... patch ... test ... commit ]*</p></div><p>When you are happy with the state of this change, you can pull it into the
884 "test" branch in preparation to make it public:</p><div class="literallayout"><p>$ git checkout test && git pull . speed-up-spinlocks</p></div><p>It is unlikely that you would have any conflicts here … but you might if you
885 spent a while on this step and had also pulled new versions from upstream.</p><p>Some time later when enough time has passed and testing done, you can pull the
886 same branch into the "release" tree ready to go upstream. This is where you
887 see the value of keeping each patch (or patch series) in its own branch. It
888 means that the patches can be moved into the "release" tree in any order.</p><div class="literallayout"><p>$ git checkout release && git pull . speed-up-spinlocks</p></div><p>After a while, you will have a number of branches, and despite the
889 well chosen names you picked for each of them, you may forget what
890 they are for, or what status they are in. To get a reminder of what
891 changes are in a specific branch, use:</p><div class="literallayout"><p>$ git log linux..branchname | git shortlog</p></div><p>To see whether it has already been merged into the test or release branches,
892 use:</p><div class="literallayout"><p>$ git log test..branchname</p></div><p>or</p><div class="literallayout"><p>$ git log release..branchname</p></div><p>(If this branch has not yet been merged, you will see some log entries.
893 If it has been merged, then there will be no output.)</p><p>Once a patch completes the great cycle (moving from test to release,
894 then pulled by Linus, and finally coming back into your local
895 "origin/master" branch), the branch for this change is no longer needed.
896 You detect this when the output from:</p><div class="literallayout"><p>$ git log origin..branchname</p></div><p>is empty. At this point the branch can be deleted:</p><div class="literallayout"><p>$ git branch -d branchname</p></div><p>Some changes are so trivial that it is not necessary to create a separate
897 branch and then merge into each of the test and release branches. For
898 these changes, just apply directly to the "release" branch, and then
899 merge that into the "test" branch.</p><p>To create diffstat and shortlog summaries of changes to include in a "please
900 pull" request to Linus you can use:</p><div class="literallayout"><p>$ git diff --stat origin..release</p></div><p>and</p><div class="literallayout"><p>$ git log -p origin..release | git shortlog</p></div><p>Here are some of the scripts that simplify all this even further.</p><div class="literallayout"><p>==== update script ====<br>
901 # Update a branch in my GIT tree. If the branch to be updated<br>
902 # is origin, then pull from kernel.org. Otherwise merge<br>
903 # origin/master branch into test|release branch<br>
904 <br>
906 test|release)<br>
908 ;;<br>
909 origin)<br>
910 before=$(git rev-parse refs/remotes/origin/master)<br>
911 git fetch origin<br>
912 after=$(git rev-parse refs/remotes/origin/master)<br>
913 if [ $before != $after ]<br>
914 then<br>
915 git log $before..$after | git shortlog<br>
916 fi<br>
917 ;;<br>
918 *)<br>
921 ;;<br>
923 # Merge a branch into either the test or release branch<br>
924 <br>
926 <br>
927 usage()<br>
928 {<br>
931 }<br>
932 <br>
935 usage<br>
936 }<br>
937 <br>
939 test|release)<br>
941 then<br>
944 fi<br>
946 ;;<br>
947 *)<br>
948 usage<br>
949 ;;<br>
951 # report on status of my ia64 GIT tree<br>
952 <br>
956 <br>
958 then<br>
959 echo $rb Warning: commits in release that are not in test $restore<br>
960 git log test..release<br>
961 fi<br>
962 <br>
963 for branch in `git show-ref --heads | sed 's|^.*/||'`<br>
964 do<br>
965 if [ $branch = test -o $branch = release ]<br>
966 then<br>
967 continue<br>
968 fi<br>
969 <br>
971 status=<br>
972 for ref in test release origin/master<br>
973 do<br>
975 then<br>
977 fi<br>
978 done<br>
979 case $status in<br>
980 trl)<br>
981 echo $rb Need to pull into test $restore<br>
982 ;;<br>
983 rl)<br>
985 ;;<br>
986 l)<br>
988 ;;<br>
990 echo $rb All done $restore<br>
991 ;;<br>
992 *)<br>
994 ;;<br>
995 esac<br>
996 git log origin/master..$branch | git shortlog<br>
997 done</p></div></div></div></div><div class="chapter" title="Chapter 5. Rewriting history and maintaining patch series"><div class="titlepage"><div><div><h2 class="title"><a name="cleaning-up-history"></a>Chapter 5. Rewriting history and maintaining patch series</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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="#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></div><p>Normally commits are only added to a project, never taken away or
998 replaced. Git is designed with this assumption, and violating it will
999 cause git’s merge machinery (for example) to do the wrong thing.</p><p>However, there is a situation in which it can be useful to violate this
1000 assumption.</p><div class="section" title="Creating the perfect patch series"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series"></a>Creating the perfect patch series</h2></div></div></div><p>Suppose you are a contributor to a large project, and you want to add a
1001 complicated feature, and to present it to the other developers in a way
1002 that makes it easy for them to read your changes, verify that they are
1003 correct, and understand why you made each change.</p><p>If you present all of your changes as a single patch (or commit), they
1004 may find that it is too much to digest all at once.</p><p>If you present them with the entire history of your work, complete with
1005 mistakes, corrections, and dead ends, they may be overwhelmed.</p><p>So the ideal is usually to produce a series of patches such that:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
1006 Each patch can be applied in order.
1008 Each patch includes a single logical change, together with a
1009 message explaining the change.
1011 No patch introduces a regression: after applying any initial
1012 part of the series, the resulting project still compiles and
1013 works, and has no bugs that it didn’t have before.
1015 The complete series produces the same end result as your own
1016 (probably much messier!) development process did.
1017 </li></ol></div><p>We will introduce some tools that can help you do this, explain how to
1018 use them, and then explain some of the problems that can arise because
1019 you are rewriting history.</p></div><div class="section" title="Keeping a patch series up to date using git rebase"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-git-rebase"></a>Keeping a patch series up to date using git rebase</h2></div></div></div><p>Suppose that you create a branch "mywork" on a remote-tracking branch
1020 "origin", and create some commits on top of it:</p><div class="literallayout"><p>$ git checkout -b mywork origin<br>
1021 $ vi file.txt<br>
1022 $ git commit<br>
1023 $ vi otherfile.txt<br>
1024 $ git commit<br>
1025 ...</p></div><p>You have performed no merges into mywork, so it is just a simple linear
1027 \
1028 a--b--c <-- mywork</pre><p>Some more interesting work has been done in the upstream project, and
1030 \
1031 a--b--c <-- mywork</pre><p>At this point, you could use "pull" to merge your changes back in;
1032 the result would create a new merge commit, like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
1033 \ \
1034 a--b--c--m <-- mywork</pre><p>However, if you prefer to keep the history in mywork a simple series of
1035 commits without any merges, you may instead choose to use
1036 <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a>:</p><div class="literallayout"><p>$ git checkout mywork<br>
1037 $ git rebase origin</p></div><p>This will remove each of your commits from mywork, temporarily saving
1038 them as patches (in a directory named ".git/rebase-apply"), update mywork to
1039 point at the latest version of origin, then apply each of the saved
1040 patches to the new mywork. The result will look like:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
1041 \
1042 a'--b'--c' <-- mywork</pre><p>In the process, it may discover conflicts. In that case it will stop
1043 and allow you to fix the conflicts; after fixing conflicts, use <code class="literal">git add</code>
1044 to update the index with those contents, and then, instead of
1045 running <code class="literal">git commit</code>, just run</p><div class="literallayout"><p>$ git rebase --continue</p></div><p>and git will continue applying the rest of the patches.</p><p>At any point you may use the <code class="literal">--abort</code> option to abort this process and
1046 return mywork to the state it had before you started the rebase:</p><div class="literallayout"><p>$ git rebase --abort</p></div></div><div class="section" title="Rewriting a single commit"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="rewriting-one-commit"></a>Rewriting a single commit</h2></div></div></div><p>We saw in <a class="xref" href="#fixing-a-mistake-by-rewriting-history" title="Fixing a mistake by rewriting history">the section called “Fixing a mistake by rewriting history”</a> that you can replace the
1047 most recent commit using</p><div class="literallayout"><p>$ git commit --amend</p></div><p>which will replace the old commit by a new commit incorporating your
1048 changes, giving you a chance to edit the old commit message first.</p><p>You can also use a combination of this and <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a> to
1049 replace a commit further back in your history and recreate the
1050 intervening changes on top of it. First, tag the problematic commit
1051 with</p><div class="literallayout"><p>$ git tag bad mywork~5</p></div><p>(Either gitk or <code class="literal">git log</code> may be useful for finding the commit.)</p><p>Then check out that commit, edit it, and rebase the rest of the series
1052 on top of it (note that we could check out the commit on a temporary
1053 branch, but instead we’re using a <a class="link" href="#detached-head" title="Examining an old version without creating a new branch">detached head</a>):</p><div class="literallayout"><p>$ git checkout bad<br>
1054 $ # make changes here and update the index<br>
1055 $ git commit --amend<br>
1056 $ git rebase --onto HEAD bad mywork</p></div><p>When you’re done, you’ll be left with mywork checked out, with the top
1057 patches on mywork reapplied on top of your modified commit. You can
1058 then clean up with</p><div class="literallayout"><p>$ git tag -d bad</p></div><p>Note that the immutable nature of git history means that you haven’t really
1059 "modified" existing commits; instead, you have replaced the old commits with
1060 new commits having new object names.</p></div><div class="section" title="Reordering or selecting from a patch series"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="reordering-patch-series"></a>Reordering or selecting from a patch series</h2></div></div></div><p>Given one existing commit, the <a class="ulink" href="git-cherry-pick.html" target="_top">git-cherry-pick(1)</a> command
1061 allows you to apply the change introduced by that commit and create a
1062 new commit that records it. So, for example, if "mywork" points to a
1063 series of patches on top of "origin", you might do something like:</p><div class="literallayout"><p>$ git checkout -b mywork-new origin<br>
1064 $ gitk origin..mywork &</p></div><p>and browse through the list of patches in the mywork branch using gitk,
1065 applying them (possibly in a different order) to mywork-new using
1066 cherry-pick, and possibly modifying them as you go using <code class="literal">git commit --amend</code>.
1067 The <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> command may also help as it allows you to
1068 individually select diff hunks for inclusion in the index (by
1069 right-clicking on the diff hunk and choosing "Stage Hunk for Commit").</p><p>Another technique is to use <code class="literal">git format-patch</code> to create a series of
1070 patches, then reset the state to before the patches:</p><div class="literallayout"><p>$ git format-patch origin<br>
1071 $ git reset --hard origin</p></div><p>Then modify, reorder, or eliminate patches as preferred before applying
1072 them again with <a class="ulink" href="git-am.html" target="_top">git-am(1)</a>.</p></div><div class="section" title="Other tools"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series-tools"></a>Other tools</h2></div></div></div><p>There are numerous other tools, such as StGit, which exist for the
1073 purpose of maintaining a patch series. These are outside of the scope of
1074 this manual.</p></div><div class="section" title="Problems with rewriting history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="problems-With-rewriting-history"></a>Problems with rewriting history</h2></div></div></div><p>The primary problem with rewriting the history of a branch has to do
1075 with merging. Suppose somebody fetches your branch and merges it into
1076 their branch, with a result something like this:</p><pre class="literallayout"> o--o--O--o--o--o <-- origin
1077 \ \
1078 t--t--t--m <-- their branch:</pre><p>Then suppose you modify the last three commits:</p><pre class="literallayout"> o--o--o <-- new head of origin
1079 /
1080 o--o--O--o--o--o <-- old head of origin</pre><p>If we examined all this history together in one repository, it will
1082 /
1083 o--o--O--o--o--o <-- old head of origin
1084 \ \
1085 t--t--t--m <-- their branch:</pre><p>Git has no way of knowing that the new head is an updated version of
1086 the old head; it treats this situation exactly the same as it would if
1087 two developers had independently done the work on the old and new heads
1088 in parallel. At this point, if someone attempts to merge the new head
1089 in to their branch, git will attempt to merge together the two (old and
1090 new) lines of development, instead of trying to replace the old by the
1091 new. The results are likely to be unexpected.</p><p>You may still choose to publish branches whose history is rewritten,
1092 and it may be useful for others to be able to fetch those branches in
1093 order to examine or test them, but they should not attempt to pull such
1094 branches into their own work.</p><p>For true distributed development that supports proper merging,
1095 published branches should never be rewritten.</p></div><div class="section" title="Why bisecting merge commits can be harder than bisecting linear history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="bisect-merges"></a>Why bisecting merge commits can be harder than bisecting linear history</h2></div></div></div><p>The <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command correctly handles history that
1096 includes merge commits. However, when the commit that it finds is a
1097 merge commit, the user may need to work harder than usual to figure out
1098 why that commit introduced a problem.</p><p>Imagine this history:</p><pre class="literallayout"> ---Z---o---X---...---o---A---C---D
1099 \ /
1100 o---o---Y---...---o---B</pre><p>Suppose that on the upper line of development, the meaning of one
1101 of the functions that exists at Z is changed at commit X. The
1102 commits from Z leading to A change both the function’s
1103 implementation and all calling sites that exist at Z, as well
1104 as new calling sites they add, to be consistent. There is no
1105 bug at A.</p><p>Suppose that in the meantime on the lower line of development somebody
1106 adds a new calling site for that function at commit Y. The
1107 commits from Z leading to B all assume the old semantics of that
1108 function and the callers and the callee are consistent with each
1109 other. There is no bug at B, either.</p><p>Suppose further that the two development lines merge cleanly at C,
1110 so no conflict resolution is required.</p><p>Nevertheless, the code at C is broken, because the callers added
1111 on the lower line of development have not been converted to the new
1112 semantics introduced on the upper line of development. So if all
1113 you know is that D is bad, that Z is good, and that
1114 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> identifies C as the culprit, how will you
1115 figure out that the problem is due to this change in semantics?</p><p>When the result of a <code class="literal">git bisect</code> is a non-merge commit, you should
1116 normally be able to discover the problem by examining just that commit.
1117 Developers can make this easy by breaking their changes into small
1118 self-contained commits. That won’t help in the case above, however,
1119 because the problem isn’t obvious from examination of any single
1120 commit; instead, a global view of the development is required. To
1121 make matters worse, the change in semantics in the problematic
1122 function may be just one small part of the changes in the upper
1123 line of development.</p><p>On the other hand, if instead of merging at C you had rebased the
1124 history between Z to B on top of A, you would have gotten this
1125 linear history:</p><pre class="literallayout"> ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*</pre><p>Bisecting between Z and D* would hit a single culprit commit Y*,
1126 and understanding why Y* was broken would probably be easier.</p><p>Partly for this reason, many experienced git users, even when
1127 working on an otherwise merge-heavy project, keep the history
1128 linear by rebasing against the latest upstream version before
1129 publishing.</p></div></div><div class="chapter" title="Chapter 6. Advanced branch management"><div class="titlepage"><div><div><h2 class="title"><a name="advanced-branch-management"></a>Chapter 6. Advanced branch management</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><div class="section" title="Fetching individual branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-individual-branches"></a>Fetching individual branches</h2></div></div></div><p>Instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just
1130 to update one branch at a time, and to store it locally under an
1131 arbitrary name:</p><div class="literallayout"><p>$ git fetch origin todo:my-todo-work</p></div><p>The first argument, "origin", just tells git to fetch from the
1132 repository you originally cloned from. The second argument tells git
1133 to fetch the branch named "todo" from the remote repository, and to
1134 store it locally under the name refs/heads/my-todo-work.</p><p>You can also fetch branches from other repositories; so</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:example-master</p></div><p>will create a new branch named "example-master" and store in it the
1135 branch named "master" from the repository at the given URL. If you
1136 already have a branch named example-master, it will attempt to
1137 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> to the commit given by example.com’s
1138 master branch. In more detail:</p></div><div class="section" title="git fetch and fast-forwards"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetch-fast-forwards"></a>git fetch and fast-forwards</h2></div></div></div><p>In the previous example, when updating an existing branch, "git fetch"
1139 checks to make sure that the most recent commit on the remote
1140 branch is a descendant of the most recent commit on your copy of the
1141 branch before updating your copy of the branch to point at the new
1142 commit. Git calls this process a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>.</p><p>A fast-forward looks something like this:</p><pre class="literallayout"> o--o--o--o <-- old head of the branch
1143 \
1144 o--o--o <-- new head of the branch</pre><p>In some cases it is possible that the new head will <span class="strong"><strong>not</strong></span> actually be
1145 a descendant of the old head. For example, the developer may have
1146 realized she made a serious mistake, and decided to backtrack,
1147 resulting in a situation like:</p><pre class="literallayout"> o--o--o--o--a--b <-- old head of the branch
1148 \
1149 o--o--o <-- new head of the branch</pre><p>In this case, "git fetch" will fail, and print out a warning.</p><p>In that case, you can still force git to update to the new head, as
1150 described in the following section. However, note that in the
1152 unless you’ve already created a reference of your own pointing to
1153 them.</p></div><div class="section" title="Forcing git fetch to do non-fast-forward updates"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="forcing-fetch"></a>Forcing git fetch to do non-fast-forward updates</h2></div></div></div><p>If git fetch fails because the new head of a branch is not a
1154 descendant of the old head, you may force the update with:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git +master:refs/remotes/example/master</p></div><p>Note the addition of the "+" sign. Alternatively, you can use the "-f"
1155 flag to force updates of all the fetched branches, as in:</p><div class="literallayout"><p>$ git fetch -f origin</p></div><p>Be aware that commits that the old version of example/master pointed at
1156 may be lost, as we saw in the previous section.</p></div><div class="section" title="Configuring remote-tracking branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="remote-branch-configuration"></a>Configuring remote-tracking branches</h2></div></div></div><p>We saw above that "origin" is just a shortcut to refer to the
1157 repository that you originally cloned from. This information is
1158 stored in git configuration variables, which you can see using
1159 <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p><div class="literallayout"><p>$ git config -l<br>
1161 core.filemode=true<br>
1162 core.logallrefupdates=true<br>
1163 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git<br>
1164 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*<br>
1165 branch.master.remote=origin<br>
1166 branch.master.merge=refs/heads/master</p></div><p>If there are other repositories that you also use frequently, you can
1167 create similar configuration options to save typing; for example,
1168 after</p><div class="literallayout"><p>$ git config remote.example.url git://example.com/proj.git</p></div><p>then the following two commands will do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:refs/remotes/example/master<br>
1169 $ git fetch example master:refs/remotes/example/master</p></div><p>Even better, if you add one more option:</p><div class="literallayout"><p>$ git config remote.example.fetch master:refs/remotes/example/master</p></div><p>then the following commands will all do the same thing:</p><div class="literallayout"><p>$ git fetch git://example.com/proj.git master:refs/remotes/example/master<br>
1170 $ git fetch example master:refs/remotes/example/master<br>
1171 $ git fetch example</p></div><p>You can also add a "+" to force the update each time:</p><div class="literallayout"><p>$ git config remote.example.fetch +master:ref/remotes/example/master</p></div><p>Don’t do this unless you’re sure you won’t mind "git fetch" possibly
1172 throwing away commits on <span class="emphasis"><em>example/master</em></span>.</p><p>Also note that all of the above configuration can be performed by
1173 directly editing the file .git/config instead of using
1174 <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>.</p><p>See <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration
1175 options mentioned above.</p></div></div><div class="chapter" title="Chapter 7. Git concepts"><div class="titlepage"><div><div><h2 class="title"><a name="git-concepts"></a>Chapter 7. Git concepts</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><p>Git is built on a small number of simple but powerful ideas. While it
1176 is possible to get things done without understanding them, you will find
1177 git much more intuitive if you do.</p><p>We start with the most important, the <a class="link" href="#def_object_database">object database</a> and the <a class="link" href="#def_index">index</a>.</p><div class="section" title="The Object Database"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-object-database"></a>The Object Database</h2></div></div></div><p>We already saw in <a class="xref" href="#understanding-commits" title="Understanding History: Commits">the section called “Understanding History: Commits”</a> that all commits are stored
1179 represent the history of a project is stored in objects with such names.
1180 In each case the name is calculated by taking the SHA-1 hash of the
1181 contents of the object. The SHA-1 hash is a cryptographic hash function.
1182 What that means to us is that it is impossible to find two different
1183 objects with the same name. This has a number of advantages; among
1184 others:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1185 Git can quickly determine whether two objects are identical or not,
1186 just by comparing names.
1188 Since object names are computed the same way in every repository, the
1189 same content stored in two repositories will always be stored under
1190 the same name.
1192 Git can detect errors when it reads an object, by checking that the
1193 object’s name is still the SHA-1 hash of its contents.
1194 </li></ul></div><p>(See <a class="xref" href="#object-details" title="Object storage format">the section called “Object storage format”</a> for the details of the object formatting and
1195 SHA-1 calculation.)</p><p>There are four different types of objects: "blob", "tree", "commit", and
1200 "blob" objects into a directory structure. In addition, a tree object
1201 can refer to other tree objects, thus creating a directory hierarchy.
1203 A <a class="link" href="#def_commit_object">"commit" object</a> ties such directory hierarchies
1205 commit contains the object name of exactly one tree designating the
1206 directory hierarchy at the time of the commit. In addition, a commit
1207 refers to "parent" commit objects that describe the history of how we
1208 arrived at that directory hierarchy.
1211 used to sign other objects. It contains the object name and type of
1212 another object, a symbolic name (of course!) and, optionally, a
1213 signature.
1214 </li></ul></div><p>The object types in some more detail:</p><div class="section" title="Commit Object"><div class="titlepage"><div><div><h3 class="title"><a name="commit-object"></a>Commit Object</h3></div></div></div><p>The "commit" object links a physical state of a tree with a description
1215 of how we got there and why. Use the --pretty=raw option to
1216 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> or <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> to examine your favorite
1219 tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf<br>
1223 <br>
1224 Fix misspelling of 'suppress' in docs<br>
1225 <br>
1226 Signed-off-by: Junio C Hamano <gitster@pobox.com></p></div><p>As you can see, a commit is defined by:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1227 a tree: The SHA-1 name of a tree object (as defined below), representing
1228 the contents of a directory at a certain point in time.
1230 parent(s): The SHA-1 name of some number of commits which represent the
1231 immediately previous step(s) in the history of the project. The
1232 example above has one parent; merge commits may have more than
1233 one. A commit with no parents is called a "root" commit, and
1234 represents the initial revision of a project. Each project must have
1235 at least one root. A project can also have multiple roots, though
1236 that isn’t common (or necessarily a good idea).
1238 an author: The name of the person responsible for this change, together
1239 with its date.
1241 a committer: The name of the person who actually created the commit,
1242 with the date it was done. This may be different from the author, for
1243 example, if the author was someone who wrote a patch and emailed it
1244 to the person who used it to create the commit.
1246 a comment describing this commit.
1247 </li></ul></div><p>Note that a commit does not itself contain any information about what
1248 actually changed; all changes are calculated by comparing the contents
1249 of the tree referred to by this commit with the trees associated with
1250 its parents. In particular, git does not attempt to record file renames
1251 explicitly, though it can identify cases where the existence of the same
1252 file data at changing paths suggests a rename. (See, for example, the
1253 -M option to <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>).</p><p>A commit is usually created by <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>, which creates a
1254 commit whose parent is normally the current HEAD, and whose tree is
1255 taken from the content currently stored in the index.</p></div><div class="section" title="Tree Object"><div class="titlepage"><div><div><h3 class="title"><a name="tree-object"></a>Tree Object</h3></div></div></div><p>The ever-versatile <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command can also be used to
1256 examine tree objects, but <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a> will give you more
1266 ...</p></div><p>As you can see, a tree object contains a list of entries, each with a
1267 mode, object type, SHA-1 name, and name, sorted by name. It represents
1268 the contents of a single directory tree.</p><p>The object type may be a blob, representing the contents of a file, or
1269 another tree, representing the contents of a subdirectory. Since trees
1270 and blobs, like all other objects, are named by the SHA-1 hash of their
1271 contents, two trees have the same SHA-1 name if and only if their
1272 contents (including, recursively, the contents of all subdirectories)
1273 are identical. This allows git to quickly determine the differences
1274 between two related tree objects, since it can ignore any entries with
1275 identical object names.</p><p>(Note: in the presence of submodules, trees may also have commits as
1276 entries. See <a class="xref" href="#submodules" title="Chapter 8. Submodules">Chapter 8, <i>Submodules</i></a> for documentation.)</p><p>Note that the files all have mode 644 or 755: git actually only pays
1277 attention to the executable bit.</p></div><div class="section" title="Blob Object"><div class="titlepage"><div><div><h3 class="title"><a name="blob-object"></a>Blob Object</h3></div></div></div><p>You can use <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> to examine the contents of a blob; take,
1278 for example, the blob in the entry for "COPYING" from the tree above:</p><div class="literallayout"><p>$ git show 6ff87c4664<br>
1279 <br>
1280 Note that the only valid version of the GPL as far as this project<br>
1281 is concerned is _this_ particular version of the license (ie v2, not<br>
1282 v2.2 or v3.x or whatever), unless explicitly otherwise stated.<br>
1284 to anything else or have attributes of any kind.</p><p>Since the blob is entirely defined by its data, if two files in a
1285 directory tree (or in multiple different versions of the repository)
1286 have the same contents, they will share the same blob object. The object
1287 is totally independent of its location in the directory tree, and
1288 renaming a file does not change the object that file is associated with.</p><p>Note that any tree or blob object can be examined using
1289 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> with the <revision>:<path> syntax. This can
1290 sometimes be useful for browsing the contents of a tree that is not
1291 currently checked out.</p></div><div class="section" title="Trust"><div class="titlepage"><div><div><h3 class="title"><a name="trust"></a>Trust</h3></div></div></div><p>If you receive the SHA-1 name of a blob from one source, and its contents
1292 from another (possibly untrusted) source, you can still trust that those
1293 contents are correct as long as the SHA-1 name agrees. This is because
1294 the SHA-1 is designed so that it is infeasible to find different contents
1295 that produce the same hash.</p><p>Similarly, you need only trust the SHA-1 name of a top-level tree object
1296 to trust the contents of the entire directory that it refers to, and if
1297 you receive the SHA-1 name of a commit from a trusted source, then you
1298 can easily verify the entire history of commits reachable through
1299 parents of that commit, and all of those contents of the trees referred
1300 to by those commits.</p><p>So to introduce some real trust in the system, the only thing you need
1301 to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the
1302 name of a top-level commit. Your digital signature shows others
1303 that you trust that commit, and the immutability of the history of
1304 commits tells others that they can trust the whole history.</p><p>In other words, you can easily validate a whole archive by just
1305 sending out a single email that tells the people the name (SHA-1 hash)
1306 of the top commit, and digitally sign that email using something
1307 like GPG/PGP.</p><p>To assist in this, git also provides the tag object…</p></div><div class="section" title="Tag Object"><div class="titlepage"><div><div><h3 class="title"><a name="tag-object"></a>Tag Object</h3></div></div></div><p>A tag object contains an object, object type, tag name, the name of the
1308 person ("tagger") who created the tag, and a message, which may contain
1309 a signature, as can be seen using <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a>:</p><div class="literallayout"><p>$ git cat-file tag v1.5.0<br>
1311 type commit<br>
1314 <br>
1316 -----BEGIN PGP SIGNATURE-----<br>
1318 <br>
1319 iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui<br>
1320 nLE/L9aUXdWeTFPron96DLA=<br>
1322 -----END PGP SIGNATURE-----</p></div><p>See the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command to learn how to create and verify tag
1323 objects. (Note that <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> can also be used to create
1324 "lightweight tags", which are not tag objects at all, but just simple
1325 references whose names begin with "refs/tags/").</p></div><div class="section" title="How git stores objects efficiently: pack files"><div class="titlepage"><div><div><h3 class="title"><a name="pack-files"></a>How git stores objects efficiently: pack files</h3></div></div></div><p>Newly created objects are initially created in a file named after the
1326 object’s SHA-1 hash (stored in .git/objects).</p><p>Unfortunately this system becomes inefficient once a project has a
1327 lot of objects. Try this on an old project:</p><div class="literallayout"><p>$ git count-objects<br>
1328 6930 objects, 47620 kilobytes</p></div><p>The first number is the number of objects which are kept in
1329 individual files. The second is the amount of space taken up by
1330 those "loose" objects.</p><p>You can save space and make git faster by moving these loose objects in
1331 to a "pack file", which stores a group of objects in an efficient
1332 compressed format; the details of how pack files are formatted can be
1333 found in <a class="ulink" href="technical/pack-format.txt" target="_top">technical/pack-format.txt</a>.</p><p>To put the loose objects into a pack, just run git repack:</p><div class="literallayout"><p>$ git repack<br>
1334 Generating pack...<br>
1341 Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.</p></div><p>You can then run</p><div class="literallayout"><p>$ git prune</p></div><p>to remove any of the "loose" objects that are now contained in the
1342 pack. This will also remove any unreferenced objects (which may be
1343 created when, for example, you use "git reset" to remove a commit).
1344 You can verify that the loose objects are gone by looking at the
1346 0 objects, 0 kilobytes</p></div><p>Although the object files are gone, any commands that refer to those
1347 objects will work exactly as they did before.</p><p>The <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for
1348 you, so is normally the only high-level command you need.</p></div><div class="section" title="Dangling objects"><div class="titlepage"><div><div><h3 class="title"><a name="dangling-objects"></a>Dangling objects</h3></div></div></div><p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling
1349 objects. They are not a problem.</p><p>The most common cause of dangling objects is that you’ve rebased a
1350 branch, or you have pulled from somebody else who rebased a branch—see
1351 <a class="xref" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">Chapter 5, <i>Rewriting history and maintaining patch series</i></a>. In that case, the old head of the original
1352 branch still exists, as does everything it pointed to. The branch
1353 pointer itself just doesn’t, since you replaced it with another one.</p><p>There are also other situations that cause dangling objects. For
1355 file, but then, before you actually committed it and made it part of the
1356 bigger picture, you changed something else in that file and committed
1357 that <span class="strong"><strong>updated</strong></span> thing—the old state that you added originally ends up
1358 not being pointed to by any commit or tree, so it’s now a dangling blob
1360 there are criss-cross merges and thus more than one merge base (which is
1361 fairly unusual, but it does happen), it will generate one temporary
1362 midway tree (or possibly even more, if you had lots of criss-crossing
1363 merges and more than two merge bases) as a temporary internal merge
1364 base, and again, those are real objects, but the end result will not end
1365 up pointing to them, so they end up "dangling" in your repository.</p><p>Generally, dangling objects aren’t anything to worry about. They can
1366 even be very useful: if you screw something up, the dangling objects can
1367 be how you recover your old tree (say, you did a rebase, and realized
1368 that you really didn’t want to—you can look at what dangling objects
1369 you have, and decide to reset your head to some old dangling state).</p><p>For commits, you can just use:</p><div class="literallayout"><p>$ gitk <dangling-commit-sha-goes-here> --not --all</p></div><p>This asks for all the history reachable from the given commit but not
1370 from any branch, tag, or other reference. If you decide it’s something
1371 you want, you can always create a new reference to it, e.g.,</p><div class="literallayout"><p>$ git branch recovered-branch <dangling-commit-sha-goes-here></p></div><p>For blobs and trees, you can’t do the same, but you can still examine
1372 them. You can just do</p><div class="literallayout"><p>$ git show <dangling-blob/tree-sha-goes-here></p></div><p>to show what the contents of the blob were (or, for a tree, basically
1373 what the "ls" for that directory was), and that may give you some idea
1374 of what the operation was that left that dangling object.</p><p>Usually, dangling blobs and trees aren’t very interesting. They’re
1375 almost always the result of either being a half-way mergebase (the blob
1376 will often even have the conflict markers from a merge in it, if you
1377 have had conflicting merges that you fixed up by hand), or simply
1378 because you interrupted a "git fetch" with ^C or something like that,
1379 leaving <span class="emphasis"><em>some</em></span> of the new objects in the object database, but just
1380 dangling and useless.</p><p>Anyway, once you are sure that you’re not interested in any dangling
1381 state, you can just prune all unreachable objects:</p><div class="literallayout"><p>$ git prune</p></div><p>and they’ll be gone. But you should only run "git prune" on a quiescent
1382 repository—it’s kind of like doing a filesystem fsck recovery: you
1383 don’t want to do that while the filesystem is mounted.</p><p>(The same is true of "git fsck" itself, btw, but since
1384 <code class="literal">git fsck</code> never actually <span class="strong"><strong>changes</strong></span> the repository, it just reports
1385 on what it found, <code class="literal">git fsck</code> itself is never <span class="emphasis"><em>dangerous</em></span> to run.
1386 Running it while somebody is actually changing the repository can cause
1387 confusing and scary messages, but it won’t actually do anything bad. In
1388 contrast, running "git prune" while somebody is actively changing the
1389 repository is a <span class="strong"><strong>BAD</strong></span> idea).</p></div><div class="section" title="Recovering from repository corruption"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-from-repository-corruption"></a>Recovering from repository corruption</h3></div></div></div><p>By design, git treats data trusted to it with caution. However, even in
1390 the absence of bugs in git itself, it is still possible that hardware or
1391 operating system errors could corrupt data.</p><p>The first defense against such problems is backups. You can back up a
1392 git directory using clone, or just using cp, tar, or any other backup
1393 mechanism.</p><p>As a last resort, you can search for the corrupted objects and attempt
1394 to replace them by hand. Back up your repository before attempting this
1395 in case you corrupt things even more in the process.</p><p>We’ll assume that the problem is a single missing or corrupted blob,
1396 which is sometimes a solvable problem. (Recovering missing trees and
1397 especially commits is <span class="strong"><strong>much</strong></span> harder).</p><p>Before starting, verify that there is corruption, and figure out where
1398 it is with <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a>; this may be time-consuming.</p><p>Assume the output looks like this:</p><div class="literallayout"><p>$ git fsck --full<br>
1401 missing blob 4b9458b3786228369c63936db65827de3cc06200</p></div><p>(Typically there will be some "dangling object" messages too, but they
1402 aren’t interesting.)</p><p>Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
1403 points to it. If you could find just one copy of that missing blob
1404 object, possibly in some other repository, you could move it into
1406 still examine the tree that pointed to it with <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>,
1407 which might output something like:</p><div class="literallayout"><p>$ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8<br>
1411 ...<br>
1413 ...</p></div><p>So now you know that the missing blob was the data for a file named
1414 "myfile". And chances are you can also identify the directory—let’s
1415 say it’s in "somedirectory". If you’re lucky the missing copy might be
1416 the same as the copy you have checked out in your working tree at
1417 "somedirectory/myfile"; you can test whether that’s right with
1418 <a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a>:</p><div class="literallayout"><p>$ git hash-object -w somedirectory/myfile</p></div><p>which will create and store a blob object with the contents of
1419 somedirectory/myfile, and output the SHA-1 of that object. if you’re
1420 extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
1421 which case you’ve guessed right, and the corruption is fixed!</p><p>Otherwise, you need more information. How do you tell which version of
1422 the file has been lost?</p><p>The easiest way to do this is with:</p><div class="literallayout"><p>$ git log --raw --all --full-history -- somedirectory/myfile</p></div><p>Because you’re asking for raw output, you’ll now get something like</p><div class="literallayout"><p>commit abc<br>
1423 Author:<br>
1424 Date:<br>
1425 ...<br>
1427 <br>
1428 <br>
1429 commit xyz<br>
1430 Author:<br>
1431 Date:<br>
1432 <br>
1433 ...<br>
1434 :100644 100644 oldsha... 4b9458b... M somedirectory/myfile</p></div><p>This tells you that the immediately preceding version of the file was
1436 You also know the commit messages that went with the change from oldsha
1437 to 4b9458b and with the change from 4b9458b to newsha.</p><p>If you’ve been committing small enough changes, you may now have a good
1438 shot at reconstructing the contents of the in-between state 4b9458b.</p><p>If you can do that, you can now recreate the missing object with</p><div class="literallayout"><p>$ git hash-object -w <recreated-file></p></div><p>and your repository is good again!</p><p>(Btw, you could have ignored the fsck, and started with doing a</p><div class="literallayout"><p>$ git log --raw --all</p></div><p>and just looked for the sha of the missing object (4b9458b..) in that
1439 whole thing. It’s up to you - git does <span class="strong"><strong>have</strong></span> a lot of information, it is
1440 just missing one particular blob version.</p></div></div><div class="section" title="The index"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-index"></a>The index</h2></div></div></div><p>The index is a binary file (generally kept in .git/index) containing a
1441 sorted list of path names, each with permissions and the SHA-1 of a blob
1442 object; <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> can show you the contents of the index:</p><div class="literallayout"><p>$ git ls-files --stage<br>
1448 ...<br>
1451 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h</p></div><p>Note that in older documentation you may see the index called the
1453 properties:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p class="simpara">
1454 The index contains all the information necessary to generate a single
1455 (uniquely determined) tree object.
1456 </p><p class="simpara">For example, running <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> generates this tree object
1457 from the index, stores it in the object database, and uses it as the
1459 The index enables fast comparisons between the tree object it defines
1460 and the working tree.
1462 the last modified time). This data is not displayed above, and is not
1463 stored in the created tree object, but it can be used to determine
1464 quickly which files in the working directory differ from what was
1465 stored in the index, and thus save git from having to read all of the
1467 It can efficiently represent information about merge conflicts
1468 between different tree objects, allowing each pathname to be
1469 associated with sufficient information about the trees involved that
1470 you can create a three-way merge between them.
1471 </p><p class="simpara">We saw in <a class="xref" href="#conflict-resolution" title="Getting conflict-resolution help during a merge">the section called “Getting conflict-resolution help during a merge”</a> that during a merge the index can
1472 store multiple versions of a single file (called "stages"). The third
1473 column in the <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> output above is the stage
1474 number, and will take on values other than 0 for files with merge
1475 conflicts.</p></li></ol></div><p>The index is thus a sort of temporary staging area, which is filled with
1476 a tree which you are in the process of working on.</p><p>If you blow the index away entirely, you generally haven’t lost any
1477 information as long as you have the name of the tree that it described.</p></div></div><div class="chapter" title="Chapter 8. Submodules"><div class="titlepage"><div><div><h2 class="title"><a name="submodules"></a>Chapter 8. Submodules</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#_pitfalls_with_submodules">Pitfalls with submodules</a></span></dt></dl></div><p>Large projects are often composed of smaller, self-contained modules. For
1478 example, an embedded Linux distribution’s source tree would include every
1479 piece of software in the distribution with some local modifications; a movie
1480 player might need to build against a specific, known-working version of a
1481 decompression library; several independent programs might all share the same
1482 build scripts.</p><p>With centralized revision control systems this is often accomplished by
1483 including every module in one single repository. Developers can check out
1484 all modules or only the modules they need to work with. They can even modify
1485 files across several modules in a single commit while moving things around
1486 or updating APIs and translations.</p><p>Git does not allow partial checkouts, so duplicating this approach in Git
1487 would force developers to keep a local copy of modules they are not
1488 interested in touching. Commits in an enormous checkout would be slower
1489 than you’d expect as Git would have to scan every directory for changes.
1490 If modules have a lot of local history, clones would take forever.</p><p>On the plus side, distributed revision control systems can much better
1491 integrate with external sources. In a centralized model, a single arbitrary
1492 snapshot of the external project is exported from its own revision control
1493 and then imported into the local revision control on a vendor branch. All
1494 the history is hidden. With distributed revision control you can clone the
1495 entire external history and much more easily follow development and re-merge
1496 local changes.</p><p>Git’s submodule support allows a repository to contain, as a subdirectory, a
1497 checkout of an external project. Submodules maintain their own identity;
1498 the submodule support just stores the submodule repository location and
1499 commit ID, so other developers who clone the containing project
1500 ("superproject") can easily clone all the submodules at the same revision.
1501 Partial checkouts of the superproject are possible: you can tell Git to
1502 clone none, some or all of the submodules.</p><p>The <a class="ulink" href="git-submodule.html" target="_top">git-submodule(1)</a> command is available since Git 1.5.3. Users
1503 with Git 1.5.2 can look up the submodule commits in the repository and
1504 manually check them out; earlier versions won’t recognize the submodules at
1505 all.</p><p>To see how submodule support works, create (for example) four example
1506 repositories that can be used later as a submodule:</p><div class="literallayout"><p>$ mkdir ~/git<br>
1507 $ cd ~/git<br>
1508 $ for i in a b c d<br>
1509 do<br>
1510 mkdir $i<br>
1511 cd $i<br>
1512 git init<br>
1514 git add $i.txt<br>
1516 cd ..<br>
1517 done</p></div><p>Now create the superproject and add all the submodules:</p><div class="literallayout"><p>$ mkdir super<br>
1518 $ cd super<br>
1519 $ git init<br>
1520 $ for i in a b c d<br>
1521 do<br>
1522 git submodule add ~/git/$i $i<br>
1523 done</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>Do not use local URLs here if you plan to publish your superproject!</p></div><p>See what files <code class="literal">git submodule</code> created:</p><div class="literallayout"><p>$ ls -a<br>
1524 . .. .git .gitmodules a b c d</p></div><p>The <code class="literal">git submodule add <repo> <path></code> command does a couple of things:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1526 current directory and by default checks out the master branch.
1528 It adds the submodule’s clone path to the <a class="ulink" href="gitmodules.html" target="_top">gitmodules(5)</a> file and
1529 adds this file to the index, ready to be committed.
1531 It adds the submodule’s current commit ID to the index, ready to be
1532 committed.
1533 </li></ul></div><p>Commit the superproject:</p><div class="literallayout"><p>$ git commit -m "Add submodules a, b, c and d."</p></div><p>Now clone the superproject:</p><div class="literallayout"><p>$ cd ..<br>
1534 $ git clone super cloned<br>
1535 $ cd cloned</p></div><p>The submodule directories are there, but they’re empty:</p><div class="literallayout"><p>$ ls -a a<br>
1536 . ..<br>
1537 $ git submodule status<br>
1538 -d266b9873ad50488163457f025db7cdd9683d88b a<br>
1539 -e81d457da15309b4fef4249aba9b50187999670d b<br>
1540 -c1536a972b9affea0f16e0680ba87332dc059146 c<br>
1541 -d96249ff5d57de5de093e6baff9e0aafa5276a74 d</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The commit object names shown above would be different for you, but they
1542 should match the HEAD commit object names of your repositories. You can check
1543 it by running <code class="literal">git ls-remote ../a</code>.</p></div><p>Pulling down the submodules is a two-step process. First run <code class="literal">git submodule
1544 init</code> to add the submodule repository URLs to <code class="literal">.git/config</code>:</p><div class="literallayout"><p>$ git submodule init</p></div><p>Now use <code class="literal">git submodule update</code> to clone the repositories and check out the
1545 commits specified in the superproject:</p><div class="literallayout"><p>$ git submodule update<br>
1546 $ cd a<br>
1547 $ ls -a<br>
1548 . .. .git a.txt</p></div><p>One major difference between <code class="literal">git submodule update</code> and <code class="literal">git submodule add</code> is
1549 that <code class="literal">git submodule update</code> checks out a specific commit, rather than the tip
1550 of a branch. It’s like checking out a tag: the head is detached, so you’re not
1552 * (no branch)<br>
1553 master</p></div><p>If you want to make a change within a submodule and you have a detached head,
1554 then you should create or checkout a branch, make your changes, publish the
1555 change within the submodule, and then update the superproject to reference the
1556 new commit:</p><div class="literallayout"><p>$ git checkout master</p></div><p>or</p><div class="literallayout"><p>$ git checkout -b fix-up</p></div><p>then</p><div class="literallayout"><p>$ echo "adding a line again" >> a.txt<br>
1558 $ git push<br>
1559 $ cd ..<br>
1560 $ git diff<br>
1561 diff --git a/a b/a<br>
1563 --- a/a<br>
1564 +++ b/a<br>
1566 -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b<br>
1568 $ git add a<br>
1570 $ git push</p></div><p>You have to run <code class="literal">git submodule update</code> after <code class="literal">git pull</code> if you want to update
1571 submodules, too.</p><div class="section" title="Pitfalls with submodules"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_pitfalls_with_submodules"></a>Pitfalls with submodules</h2></div></div></div><p>Always publish the submodule change before publishing the change to the
1572 superproject that references it. If you forget to publish the submodule change,
1573 others won’t be able to clone the repository:</p><div class="literallayout"><p>$ cd ~/git/super/a<br>
1576 $ cd ..<br>
1577 $ git add a<br>
1579 $ git push<br>
1580 $ cd ~/git/cloned<br>
1581 $ git pull<br>
1582 $ git submodule update<br>
1583 error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.<br>
1584 Did you forget to 'git add'?<br>
1585 Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'</p></div><p>In older git versions it could be easily forgotten to commit new or modified
1586 files in a submodule, which silently leads to similar problems as not pushing
1588 in the superproject show submodules as modified when they contain new or
1589 modified files to protect against accidentally committing such a state. "git
1592 diff --git a/sub b/sub<br>
1593 --- a/sub<br>
1594 +++ b/sub<br>
1598 $ git diff --submodule<br>
1599 Submodule sub 3f35670..3f35670-dirty:</p></div><p>You also should not rewind branches in a submodule beyond commits that were
1600 ever recorded in any superproject.</p><p>It’s not safe to run <code class="literal">git submodule update</code> if you’ve made and committed
1601 changes within a submodule without checking out a branch first. They will be
1603 module a<br>
1606 $ cd ..<br>
1607 $ git submodule update<br>
1608 Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'<br>
1609 $ cd a<br>
1610 $ cat a.txt<br>
1611 module a</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The changes are still visible in the submodule’s reflog.</p></div><p>This is not the case if you did not commit your changes.</p></div></div><div class="chapter" title="Chapter 9. Low-level git operations"><div class="titlepage"><div><div><h2 class="title"><a name="low-level-operations"></a>Chapter 9. Low-level git operations</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><p>Many of the higher-level commands were originally implemented as shell
1612 scripts using a smaller core of low-level git commands. These can still
1613 be useful when doing unusual things with git, or just as a way to
1614 understand its inner workings.</p><div class="section" title="Object access and manipulation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-manipulation"></a>Object access and manipulation</h2></div></div></div><p>The <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> command can show the contents of any object,
1615 though the higher-level <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> is usually more useful.</p><p>The <a class="ulink" href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> command allows constructing commits with
1616 arbitrary parents and trees.</p><p>A tree can be created with <a class="ulink" href="git-write-tree.html" target="_top">git-write-tree(1)</a> and its data can be
1617 accessed by <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. Two trees can be compared with
1618 <a class="ulink" href="git-diff-tree.html" target="_top">git-diff-tree(1)</a>.</p><p>A tag is created with <a class="ulink" href="git-mktag.html" target="_top">git-mktag(1)</a>, and the signature can be
1619 verified by <a class="ulink" href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>, though it is normally simpler to
1620 use <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> for both.</p></div><div class="section" title="The Workflow"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-workflow"></a>The Workflow</h2></div></div></div><p>High-level operations such as <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>,
1621 <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a> and <a class="ulink" href="git-reset.html" target="_top">git-reset(1)</a> work by moving data
1622 between the working tree, the index, and the object database. Git
1623 provides low-level operations which perform each of these steps
1625 work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the
1626 index), but most operations move data between the index file and either
1627 the database or the working directory. Thus there are four main
1628 combinations:</p><div class="section" title="working directory → index"><div class="titlepage"><div><div><h3 class="title"><a name="working-directory-to-index"></a>working directory → index</h3></div></div></div><p>The <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a> command updates the index with
1629 information from the working directory. You generally update the
1630 index information by just specifying the filename you want to update,
1631 like so:</p><div class="literallayout"><p>$ git update-index filename</p></div><p>but to avoid common mistakes with filename globbing etc, the command
1632 will not normally add totally new entries or remove old entries,
1633 i.e. it will normally just update existing cache entries.</p><p>To tell git that yes, you really do realize that certain files no
1634 longer exist, or that new files should be added, you
1635 should use the <code class="literal">--remove</code> and <code class="literal">--add</code> flags respectively.</p><p>NOTE! A <code class="literal">--remove</code> flag does <span class="emphasis"><em>not</em></span> mean that subsequent filenames will
1636 necessarily be removed: if the files still exist in your directory
1637 structure, the index will be updated with their new status, not
1638 removed. The only thing <code class="literal">--remove</code> means is that update-index will be
1639 considering a removed file to be a valid thing, and if the file really
1640 does not exist any more, it will update the index accordingly.</p><p>As a special case, you can also do <code class="literal">git update-index --refresh</code>, which
1641 will refresh the "stat" information of each index to match the current
1642 stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and
1643 it will only update the fields that are used to quickly test whether
1644 an object still matches its old backing store object.</p><p>The previously introduced <a class="ulink" href="git-add.html" target="_top">git-add(1)</a> is just a wrapper for
1645 <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a>.</p></div><div class="section" title="index → object database"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-object-database"></a>index → object database</h3></div></div></div><p>You write your current index file to a "tree" object with the program</p><div class="literallayout"><p>$ git write-tree</p></div><p>that doesn’t come with any options—it will just write out the
1646 current index into the set of tree objects that describe that state,
1647 and it will return the name of the resulting top-level tree. You can
1648 use that tree to re-generate the index at any time by going in the
1649 other direction:</p></div><div class="section" title="object database → index"><div class="titlepage"><div><div><h3 class="title"><a name="object-database-to-index"></a>object database → index</h3></div></div></div><p>You read a "tree" file from the object database, and use that to
1650 populate (and overwrite—don’t do this if your index contains any
1651 unsaved state that you might want to restore later!) your current
1652 index. Normal operation is just</p><div class="literallayout"><p>$ git read-tree <SHA-1 of tree></p></div><p>and your index file will now be equivalent to the tree that you saved
1653 earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working
1654 directory contents have not been modified.</p></div><div class="section" title="index → working directory"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-working-directory"></a>index → working directory</h3></div></div></div><p>You update your working directory from the index by "checking out"
1655 files. This is not a very common operation, since normally you’d just
1656 keep your files updated, and rather than write to your working
1657 directory, you’d tell the index files about the changes in your
1658 working directory (i.e. <code class="literal">git update-index</code>).</p><p>However, if you decide to jump to a new version, or check out somebody
1659 else’s version, or just restore a previous tree, you’d populate your
1660 index file with read-tree, and then you need to check out the result
1661 with</p><div class="literallayout"><p>$ git checkout-index filename</p></div><p>or, if you want to check out all of the index, use <code class="literal">-a</code>.</p><p>NOTE! <code class="literal">git checkout-index</code> normally refuses to overwrite old files, so
1662 if you have an old version of the tree already checked out, you will
1663 need to use the "-f" flag (<span class="emphasis"><em>before</em></span> the "-a" flag or the filename) to
1664 <span class="emphasis"><em>force</em></span> the checkout.</p><p>Finally, there are a few odds and ends which are not purely moving
1665 from one representation to the other:</p></div><div class="section" title="Tying it all together"><div class="titlepage"><div><div><h3 class="title"><a name="tying-it-all-together"></a>Tying it all together</h3></div></div></div><p>To commit a tree you have instantiated with "git write-tree", you’d
1666 create a "commit" object that refers to that tree and the history
1667 behind it—most notably the "parent" commits that preceded it in
1669 before a certain change was made. However, sometimes it can have two
1670 or more parent commits, in which case we call it a "merge", due to the
1671 fact that such a commit brings together ("merges") two or more
1672 previous states represented by other commits.</p><p>In other words, while a "tree" represents a particular directory state
1674 and explains how we got there.</p><p>You create a commit object by giving it the tree that describes the
1675 state at the time of the commit, and a list of parents:</p><div class="literallayout"><p>$ git commit-tree <tree> -p <parent> [(-p <parent2>)...]</p></div><p>and then giving the reason for the commit on stdin (either through
1676 redirection from a pipe or file, or by just typing it at the tty).</p><p><code class="literal">git commit-tree</code> will return the name of the object that represents
1677 that commit, and you should save it away for later use. Normally,
1678 you’d commit a new <code class="literal">HEAD</code> state, and while git doesn’t care where you
1679 save the note about that state, in practice we tend to just write the
1680 result to the file pointed at by <code class="literal">.git/HEAD</code>, so that we can always see
1681 what the last committed state was.</p><p>Here is an ASCII art by Jon Loeliger that illustrates how
1683 commit obj<br>
1684 +----+<br>
1685 | |<br>
1686 | |<br>
1687 V V<br>
1688 +-----------+<br>
1689 | Object DB |<br>
1690 | Backing |<br>
1691 | Store |<br>
1692 +-----------+<br>
1693 ^<br>
1694 write-tree | |<br>
1695 tree obj | |<br>
1696 | | read-tree<br>
1697 | | tree obj<br>
1698 V<br>
1699 +-----------+<br>
1700 | Index |<br>
1702 +-----------+<br>
1703 update-index ^<br>
1704 blob obj | |<br>
1705 | |<br>
1706 checkout-index -u | | checkout-index<br>
1707 stat | | blob obj<br>
1708 V<br>
1709 +-----------+<br>
1710 | Working |<br>
1711 | Directory |<br>
1712 +-----------+</p></div></div></div><div class="section" title="Examining the data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-the-data"></a>Examining the data</h2></div></div></div><p>You can examine the data represented in the object database and the
1713 index with various helper tools. For every object, you can use
1714 <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the
1715 object:</p><div class="literallayout"><p>$ git cat-file -t <objectname></p></div><p>shows the type of the object, and once you have the type (which is
1716 usually implicit in where you find the object), you can use</p><div class="literallayout"><p>$ git cat-file blob|tree|commit|tag <objectname></p></div><p>to show its contents. NOTE! Trees have binary content, and as a result
1717 there is a special helper for showing that content, called
1720 tend to be small and fairly self-explanatory. In particular, if you
1722 you can do</p><div class="literallayout"><p>$ git cat-file commit HEAD</p></div><p>to see what the top commit was.</p></div><div class="section" title="Merging multiple trees"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees"></a>Merging multiple trees</h2></div></div></div><p>Git helps you do a three-way merge, which you can expand to n-way by
1723 repeating the merge procedure arbitrary times until you finally
1724 "commit" the state. The normal situation is that you’d only do one
1725 three-way merge (two parents), and commit it, but if you like to, you
1726 can do multiple parents in one go.</p><p>To do a three-way merge, you need the two sets of "commit" objects
1727 that you want to merge, use those to find the closest common parent (a
1728 third "commit" object), and then use those commit objects to find the
1729 state of the directory ("tree" object) at these points.</p><p>To get the "base" for the merge, you first look up the common parent
1730 of two commits with</p><div class="literallayout"><p>$ git merge-base <commit1> <commit2></p></div><p>which will return you the commit they are both based on. You should
1731 now look up the "tree" objects of those commits, which you can easily
1732 do with (for example)</p><div class="literallayout"><p>$ git cat-file commit <commitname> | head -1</p></div><p>since the tree object information is always the first line in a commit
1734 tree, aka the common tree, and the two "result" trees, aka the branches
1735 you want to merge), you do a "merge" read into the index. This will
1736 complain if it has to throw away your old index contents, so you should
1737 make sure that you’ve committed those—in fact you would normally
1738 always do a merge against your last commit (which should thus match what
1739 you have in your current index anyway).</p><p>To do the merge, do</p><div class="literallayout"><p>$ git read-tree -m -u <origtree> <yourtree> <targettree></p></div><p>which will do all trivial merge operations for you directly in the
1740 index file, and you can just write the result out with
1741 <code class="literal">git write-tree</code>.</p></div><div class="section" title="Merging multiple trees, continued"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees-2"></a>Merging multiple trees, continued</h2></div></div></div><p>Sadly, many merges aren’t trivial. If there are files that have
1742 been added, moved or removed, or if both branches have modified the
1743 same file, you will be left with an index tree that contains "merge
1744 entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree
1745 object, and you will have to resolve any such merge clashes using
1746 other tools before you can write out the result.</p><p>You can examine such index state with <code class="literal">git ls-files --unmerged</code>
1747 command. An example:</p><div class="literallayout"><p>$ git read-tree -m $orig HEAD $target<br>
1748 $ git ls-files --unmerged<br>
1751 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c</p></div><p>Each line of the <code class="literal">git ls-files --unmerged</code> output begins with
1753 filename. The <span class="emphasis"><em>stage number</em></span> is git’s way to say which tree it
1754 came from: stage 1 corresponds to <code class="literal">$orig</code> tree, stage 2 <code class="literal">HEAD</code>
1755 tree, and stage3 <code class="literal">$target</code> tree.</p><p>Earlier we said that trivial merges are done inside
1757 from <code class="literal">$orig</code> to <code class="literal">HEAD</code> nor <code class="literal">$target</code>, or if the file changed
1758 from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way,
1761 <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> in a different way.
1762 You could resolve this by running your favorite 3-way merge
1763 program, e.g. <code class="literal">diff3</code>, <code class="literal">merge</code>, or git’s own merge-file, on
1764 the blob objects from these three stages yourself, like this:</p><div class="literallayout"><p>$ git cat-file blob 263414f... >hello.c~1<br>
1767 $ git merge-file hello.c~2 hello.c~1 hello.c~3</p></div><p>This would leave the merge result in <code class="literal">hello.c~2</code> file, along
1768 with conflict markers if there are conflicts. After verifying
1769 the merge result makes sense, you can tell git what the final
1770 merge result for this file is by:</p><div class="literallayout"><p>$ mv -f hello.c~2 hello.c<br>
1771 $ git update-index hello.c</p></div><p>When a path is in the "unmerged" state, running <code class="literal">git update-index</code> for
1772 that path tells git to mark the path resolved.</p><p>The above is the description of a git merge at the lowest level,
1773 to help you understand what conceptually happens under the hood.
1774 In practice, nobody, not even git itself, runs <code class="literal">git cat-file</code> three times
1776 stages to temporary files and calls a "merge" script on it:</p><div class="literallayout"><p>$ git merge-index git-merge-one-file hello.c</p></div><p>and that is what higher level <code class="literal">git merge -s resolve</code> is implemented with.</p></div></div><div class="chapter" title="Chapter 10. Hacking git"><div class="titlepage"><div><div><h2 class="title"><a name="hacking-git"></a>Chapter 10. Hacking git</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><p>This chapter covers internal details of the git implementation which
1777 probably only git developers need to understand.</p><div class="section" title="Object storage format"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-details"></a>Object storage format</h2></div></div></div><p>All objects have a statically determined "type" which identifies the
1778 format of the object (i.e. how it is used, and how it can refer to other
1779 objects). There are currently four different object types: "blob",
1781 characteristics: they are all deflated with zlib, and have a header
1782 that not only specifies their type, but also provides size information
1783 about the data in the object. It’s worth noting that the SHA-1 hash
1784 that is used to name the object is the hash of the original data
1785 plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name
1787 (Historical note: in the dawn of the age of git the hash
1788 was the SHA-1 of the <span class="emphasis"><em>compressed</em></span> object.)</p><p>As a result, the general consistency of an object can always be tested
1789 independently of the contents or the type of the object: all objects can
1790 be validated by verifying that (a) their hashes match the content of the
1791 file and (b) the object successfully inflates to a stream of bytes that
1793 size> + <byte\0> + <binary object data>.</p><p>The structured objects can further have their structure and
1794 connectivity to other objects verified. This is generally done with
1796 of all objects, and verifies their internal consistency (in addition
1797 to just verifying their superficial consistency through the hash).</p></div><div class="section" title="A birds-eye view of Git’s source code"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="birdview-on-the-source-code"></a>A birds-eye view of Git’s source code</h2></div></div></div><p>It is not always easy for new developers to find their way through Git’s
1798 source code. This section gives you a little guidance to show where to
1799 start.</p><p>A good place to start is with the contents of the initial commit, with:</p><div class="literallayout"><p>$ git checkout e83c5163</p></div><p>The initial revision lays the foundation for almost everything git has
1800 today, but is small enough to read in one sitting.</p><p>Note that terminology has changed since that revision. For example, the
1801 README in that revision uses the word "changeset" to describe what we
1802 now call a <a class="link" href="#def_commit_object">commit</a>.</p><p>Also, we do not call it "cache" any more, but rather "index"; however, the
1803 file is still called <code class="literal">cache.h</code>. Remark: Not much reason to change it now,
1804 especially since there is no good single name for it anyway, because it is
1805 basically <span class="emphasis"><em>the</em></span> header file which is included by <span class="emphasis"><em>all</em></span> of Git’s C sources.</p><p>If you grasp the ideas in that initial commit, you should check out a
1806 more recent version and skim <code class="literal">cache.h</code>, <code class="literal">object.h</code> and <code class="literal">commit.h</code>.</p><p>In the early days, Git (in the tradition of UNIX) was a bunch of programs
1807 which were extremely simple, and which you used in scripts, piping the
1808 output of one into another. This turned out to be good for initial
1809 development, since it was easier to test new things. However, recently
1810 many of these parts have become builtins, and some of the core has been
1811 "libified", i.e. put into libgit.a for performance, portability reasons,
1812 and to avoid code duplication.</p><p>By now, you know what the index is (and find the corresponding data
1813 structures in <code class="literal">cache.h</code>), and that there are just a couple of object types
1814 (blobs, trees, commits and tags) which inherit their common structure from
1815 <code class="literal">struct object</code>, which is their first member (and thus, you can cast e.g.
1816 <code class="literal">(struct object *)commit</code> to achieve the <span class="emphasis"><em>same</em></span> as <code class="literal">&commit→object</code>, i.e.
1817 get at the object name and flags).</p><p>Now is a good point to take a break to let this information sink in.</p><p>Next step: get familiar with the object naming. Read <a class="xref" href="#naming-commits" title="Naming commits">the section called “Naming commits”</a>.
1818 There are quite a few ways to name an object (and not only revisions!).
1819 All of these are handled in <code class="literal">sha1_name.c</code>. Just have a quick look at
1821 functions like <code class="literal">get_sha1_basic()</code> or the likes.</p><p>This is just to get you into the groove for the most libified part of Git:
1822 the revision walker.</p><p>Basically, the initial version of <code class="literal">git log</code> was a shell script:</p><div class="literallayout"><p>$ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \<br>
1823 LESS=-S ${PAGER:-less}</p></div><p>What does this mean?</p><p><code class="literal">git rev-list</code> is the original version of the revision walker, which
1824 <span class="emphasis"><em>always</em></span> printed a list of revisions to stdout. It is still functional,
1825 and needs to, since most new Git commands start out as scripts using
1826 <code class="literal">git rev-list</code>.</p><p><code class="literal">git rev-parse</code> is not as important any more; it was only used to filter out
1827 options that were relevant for the different plumbing commands that were
1828 called by the script.</p><p>Most of what <code class="literal">git rev-list</code> did is contained in <code class="literal">revision.c</code> and
1829 <code class="literal">revision.h</code>. It wraps the options in a struct named <code class="literal">rev_info</code>, which
1830 controls how and what revisions are walked, and more.</p><p>The original job of <code class="literal">git rev-parse</code> is now taken by the function
1831 <code class="literal">setup_revisions()</code>, which parses the revisions and the common command line
1832 options for the revision walker. This information is stored in the struct
1833 <code class="literal">rev_info</code> for later consumption. You can do your own command line option
1834 parsing after calling <code class="literal">setup_revisions()</code>. After that, you have to call
1835 <code class="literal">prepare_revision_walk()</code> for initialization, and then you can get the
1836 commits one by one with the function <code class="literal">get_revision()</code>.</p><p>If you are interested in more details of the revision walking process,
1838 <code class="literal">git show v1.3.0~155^2~4</code> and scroll down to that function (note that you
1839 no longer need to call <code class="literal">setup_pager()</code> directly).</p><p>Nowadays, <code class="literal">git log</code> is a builtin, which means that it is <span class="emphasis"><em>contained</em></span> in the
1840 command <code class="literal">git</code>. The source side of a builtin is</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1841 a function called <code class="literal">cmd_<bla></code>, typically defined in <code class="literal">builtin-<bla>.c</code>,
1844 an entry in the <code class="literal">commands[]</code> array in <code class="literal">git.c</code>, and
1846 an entry in <code class="literal">BUILTIN_OBJECTS</code> in the <code class="literal">Makefile</code>.
1847 </li></ul></div><p>Sometimes, more than one builtin is contained in one source file. For
1848 example, <code class="literal">cmd_whatchanged()</code> and <code class="literal">cmd_log()</code> both reside in <code class="literal">builtin-log.c</code>,
1849 since they share quite a bit of code. In that case, the commands which are
1850 <span class="emphasis"><em>not</em></span> named like the <code class="literal">.c</code> file in which they live have to be listed in
1851 <code class="literal">BUILT_INS</code> in the <code class="literal">Makefile</code>.</p><p><code class="literal">git log</code> looks more complicated in C than it does in the original script,
1852 but that allows for a much greater flexibility and performance.</p><p>Here again it is a good point to take a pause.</p><p>Lesson three is: study the code. Really, it is the best way to learn about
1853 the organization of Git (after you know the basic concepts).</p><p>So, think about something which you are interested in, say, "how can I
1854 access a blob just knowing the object name of it?". The first step is to
1855 find a Git command with which you can do it. In this example, it is either
1856 <code class="literal">git show</code> or <code class="literal">git cat-file</code>.</p><p>For the sake of clarity, let’s stay with <code class="literal">git cat-file</code>, because it</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1857 is plumbing, and
1859 was around even in the initial commit (it literally went only through
1860 some 20 revisions as <code class="literal">cat-file.c</code>, was renamed to <code class="literal">builtin-cat-file.c</code>
1861 when made a builtin, and then saw less than 10 versions).
1862 </li></ul></div><p>So, look into <code class="literal">builtin-cat-file.c</code>, search for <code class="literal">cmd_cat_file()</code> and look what
1867 die("Not a valid object name %s", argv[2]);</p></div><p>Let’s skip over the obvious details; the only really interesting part
1868 here is the call to <code class="literal">get_sha1()</code>. It tries to interpret <code class="literal">argv[2]</code> as an
1869 object name, and if it refers to an object which is present in the current
1870 repository, it writes the resulting SHA-1 into the variable <code class="literal">sha1</code>.</p><p>Two things are interesting here:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
1871 <code class="literal">get_sha1()</code> returns 0 on <span class="emphasis"><em>success</em></span>. This might surprise some new
1872 Git hackers, but there is a long tradition in UNIX to return different
1873 negative numbers in case of different errors—and 0 on success.
1875 the variable <code class="literal">sha1</code> in the function signature of <code class="literal">get_sha1()</code> is <code class="literal">unsigned
1878 commit. Note that whenever a SHA-1 is passed as <code class="literal">unsigned char *</code>, it
1879 is the binary representation, as opposed to the ASCII representation in
1881 </li></ul></div><p>You will see both of these things throughout the code.</p><p>Now, for the meat:</p><div class="literallayout"><p> case 0:<br>
1882 buf = read_object_with_reference(sha1, argv[1], &size, NULL);</p></div><p>This is how you read a blob (actually, not only a blob, but any type of
1883 object). To know how the function <code class="literal">read_object_with_reference()</code> actually
1886 the source.</p><p>To find out how the result can be used, just read on in <code class="literal">cmd_cat_file()</code>:</p><div class="literallayout"><p> write_or_die(1, buf, size);</p></div><p>Sometimes, you do not know where to look for a feature. In many such cases,
1887 it helps to search through the output of <code class="literal">git log</code>, and then <code class="literal">git show</code> the
1888 corresponding commit.</p><p>Example: If you know that there was some test case for <code class="literal">git bundle</code>, but
1889 do not remember where it was (yes, you <span class="emphasis"><em>could</em></span> <code class="literal">git grep bundle t/</code>, but that
1890 does not illustrate the point!):</p><div class="literallayout"><p>$ git log --no-merges t/</p></div><p>In the pager (<code class="literal">less</code>), just search for "bundle", go a few lines back,
1891 and see that it is in commit 18449ab0… Now just copy this object name,
1892 and paste it into the command line</p><div class="literallayout"><p>$ git show 18449ab0</p></div><p>Voila.</p><p>Another example: Find out what to do in order to make some script a
1893 builtin:</p><div class="literallayout"><p>$ git log --no-merges --diff-filter=A builtin-*.c</p></div><p>You see, Git is actually the best tool to find out about the source of Git
1894 itself!</p></div></div><div class="chapter" title="Chapter 11. Git Glossary"><div class="titlepage"><div><div><h2 class="title"><a name="glossary"></a>Chapter 11. Git Glossary</h2></div></div></div><div class="variablelist"><dl><dt><span class="term">
1896 </span></dt><dd>
1899 from another object database, which is called "alternate".
1902 </span></dt><dd>
1903 A bare repository is normally an appropriately
1904 named <a class="link" href="#def_directory">directory</a> with a <code class="literal">.git</code> suffix that does not
1905 have a locally checked-out copy of any of the files under
1907 administrative and control files that would normally be present in the
1910 and no other files are present and checked out. Usually publishers of
1911 public repositories make bare repositories available.
1914 </span></dt><dd>
1918 </span></dt><dd>
1919 A "branch" is an active line of development. The most recent
1921 that branch. The tip of the branch is referenced by a branch
1923 is done on the branch. A single git
1930 </span></dt><dd>
1934 </span></dt><dd>
1935 A list of objects, where each <a class="link" href="#def_object">object</a> in the list contains
1936 a reference to its successor (for example, the successor of a
1937 <a class="link" href="#def_commit">commit</a> could be one of its <a class="link" href="#def_parent">parents</a>).
1940 </span></dt><dd>
1942 store changes, but states, it really does not make sense to use the term
1943 "changesets" with git.
1946 </span></dt><dd>
1947 The action of updating all or part of the
1948 <a class="link" href="#def_working_tree">working tree</a> with a <a class="link" href="#def_tree_object">tree object</a>
1951 <a class="link" href="#def_index">index</a> and <a class="link" href="#def_HEAD">HEAD</a> if the whole working tree has
1955 </span></dt><dd>
1957 changes out of a series of changes (typically commits) and record them
1958 as a new series of changes on top of a different codebase. In GIT, this is
1959 performed by the "git cherry-pick" command to extract the change introduced
1964 </span></dt><dd>
1967 <a class="link" href="#def_head">head</a>. Also see "<a class="link" href="#def_dirty">dirty</a>".
1971 As a noun: A single point in the
1972 git history; the entire history of a project is represented as a
1973 set of interrelated commits. The word "commit" is often
1974 used by git in the same places other revision control systems
1978 state in the git history, by creating a new commit representing the current
1979 state of the <a class="link" href="#def_index">index</a> and advancing <a class="link" href="#def_HEAD">HEAD</a>
1982 </span></dt><dd>
1984 particular <a class="link" href="#def_revision">revision</a>, such as <a class="link" href="#def_parent">parents</a>, committer,
1987 revision.
1990 </span></dt><dd>
1991 Fundamental data structures and utilities of git. Exposes only limited
1992 source code management tools.
1995 </span></dt><dd>
1996 Directed acyclic graph. The <a class="link" href="#def_commit_object">commit objects</a> form a
1997 directed acyclic graph, because they have parents (directed), and the
2002 </span></dt><dd>
2005 dangling object has no references to it from any
2006 reference or <a class="link" href="#def_object">object</a> in the <a class="link" href="#def_repository">repository</a>.
2009 </span></dt><dd>
2011 <a class="link" href="#def_branch">branch</a>. However, git also allows you to <a class="link" href="#def_checkout">check out</a>
2012 an arbitrary <a class="link" href="#def_commit">commit</a> that isn’t necessarily the tip of any
2013 particular branch. In this case HEAD is said to be "detached".
2016 </span></dt><dd>
2017 You are <span class="strong"><strong>waaaaay</strong></span> behind. See <a class="link" href="#def_index">index</a>.
2020 </span></dt><dd>
2021 The list you get with "ls" :-)
2024 </span></dt><dd>
2026 it contains modifications which have not been <a class="link" href="#def_commit">committed</a> to the current
2030 </span></dt><dd>
2031 Favorite synonym to "<a class="link" href="#def_tree-ish">tree-ish</a>" by some total geeks. See
2033 explanation. Avoid this term, not to confuse people.
2036 </span></dt><dd>
2041 </span></dt><dd>
2042 A fast-forward is a special type of <a class="link" href="#def_merge">merge</a> where you have a
2045 you have. In such these cases, you do not make a new <a class="link" href="#def_merge">merge</a>
2047 revision. This will happen frequently on a
2052 </span></dt><dd>
2057 and to get them, too. See also <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
2060 </span></dt><dd>
2061 Linus Torvalds originally designed git to be a user space file system,
2062 i.e. the infrastructure to hold files and directories. That ensured the
2063 efficiency and speed of git.
2066 </span></dt><dd>
2070 </span></dt><dd>
2071 Grafts enables two otherwise different lines of development to be joined
2072 together by recording fake ancestry information for commits. This way
2073 you can make git pretend the set of <a class="link" href="#def_parent">parents</a> a <a class="link" href="#def_commit">commit</a> has
2074 is different from what was recorded when the commit was
2078 </span></dt><dd>
2082 </span></dt><dd>
2083 A <a class="link" href="#def_ref">named reference</a> to the <a class="link" href="#def_commit">commit</a> at the tip of a
2089 </span></dt><dd>
2090 The current <a class="link" href="#def_branch">branch</a>. In more detail: Your <a class="link" href="#def_working_tree">working tree</a> is normally derived from the state of the tree
2091 referred to by HEAD. HEAD is a reference to one of the
2094 reference an arbitrary commit.
2097 </span></dt><dd>
2101 </span></dt><dd>
2102 During the normal execution of several git commands, call-outs are made
2103 to optional scripts that allow a developer to add functionality or
2104 checking. Typically, the hooks allow for a command to be pre-verified
2105 and potentially aborted, and allow for a post-notification after the
2106 operation is done. The hook scripts are found in the
2108 removing the <code class="literal">.sample</code> suffix from the filename. In earlier versions
2109 of git you had to make them executable.
2112 </span></dt><dd>
2113 A collection of files with stat information, whose contents are stored
2114 as objects. The index is a stored version of your
2115 <a class="link" href="#def_working_tree">working tree</a>. Truth be told, it can also contain a second, and even
2116 a third version of a working tree, which are used
2120 </span></dt><dd>
2121 The information regarding a particular file, stored in the
2124 the index contains multiple versions of that file).
2127 </span></dt><dd>
2130 "master" is created, and becomes the active branch. In most
2131 cases, this contains the local development, though that is
2132 purely by convention and is not required.
2136 As a verb: To bring the contents of another
2139 case where the merged-in branch is from a different repository,
2141 and then merging the result into the current branch. This
2142 combination of fetch and merge operations is called a
2144 that identifies changes made since the branches diverged, and
2145 then applies all those changes together. In cases where changes
2146 conflict, manual intervention may be required to complete the
2147 merge.
2148 </p><p class="simpara">As a noun: unless it is a <a class="link" href="#def_fast_forward">fast-forward</a>, a
2149 successful merge results in the creation of a new <a class="link" href="#def_commit">commit</a>
2150 representing the result of the merge, and having as
2151 <a class="link" href="#def_parent">parents</a> the tips of the merged <a class="link" href="#def_branch">branches</a>.
2152 This commit is referred to as a "merge commit", or sometimes just a
2155 </span></dt><dd>
2156 The unit of storage in git. It is uniquely identified by the
2158 object can not be changed.
2161 </span></dt><dd>
2167 </span></dt><dd>
2171 </span></dt><dd>
2172 The unique identifier of an <a class="link" href="#def_object">object</a>. The <a class="link" href="#def_hash">hash</a>
2173 of the object’s contents using the Secure Hash Algorithm
2178 </span></dt><dd>
2180 "<a class="link" href="#def_tree_object">tree</a>", "<a class="link" href="#def_tag_object">tag</a>" or
2185 </span></dt><dd>
2186 To <a class="link" href="#def_merge">merge</a> more than two <a class="link" href="#def_branch">branches</a>. Also denotes an
2187 intelligent predator.
2190 </span></dt><dd>
2192 at least one upstream project which they track. By default
2194 will be fetched into remote <a class="link" href="#def_remote_tracking_branch">remote-tracking branches</a> named
2195 origin/name-of-upstream-branch, which you can see using
2199 </span></dt><dd>
2200 A set of objects which have been compressed into one file (to save space
2201 or to transmit them efficiently).
2204 </span></dt><dd>
2205 The list of identifiers, and other information, of the objects in a
2206 <a class="link" href="#def_pack">pack</a>, to assist in efficiently accessing the contents of a
2207 pack.
2211 Pattern used to specify paths.
2214 limit the scope of operations to some subset of the tree or
2215 worktree. See the documentation of each command for whether
2216 paths are relative to the current directory or toplevel. The
2217 pathspec syntax is as follows:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
2218 any path matches itself
2220 the pathspec up to the last slash represents a
2221 directory prefix. The scope of that pathspec is
2222 limited to that subtree.
2224 the rest of the pathspec is a pattern for the remainder
2225 of the pathname. Paths relative to the directory
2226 prefix will be matched against that pattern using fnmatch(3);
2227 in particular, <span class="emphasis"><em>*</em></span> and <span class="emphasis"><em>?</em></span> <span class="emphasis"><em>can</em></span> match directory separators.
2229 in the Documentation subtree,
2230 including Documentation/chapter_1/figure_1.jpg.</p></li></ul></div></dd><dt><span class="term">
2232 </span></dt><dd>
2234 of the logical predecessor(s) in the line of development, i.e. its
2235 parents.
2238 </span></dt><dd>
2240 routines that help select changes that add or delete a given text
2241 string. With the <code class="literal">--pickaxe-all</code> option, it can be used to view the full
2243 particular line of text. See <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>.
2246 </span></dt><dd>
2250 </span></dt><dd>
2251 Cute name for programs and program suites depending on
2257 </span></dt><dd>
2258 Pulling a <a class="link" href="#def_branch">branch</a> means to <a class="link" href="#def_fetch">fetch</a> it and
2259 <a class="link" href="#def_merge">merge</a> it. See also <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.
2262 </span></dt><dd>
2264 <a class="link" href="#def_head_ref">head ref</a> from a remote <a class="link" href="#def_repository">repository</a>,
2265 find out if it is a direct ancestor to the branch’s local
2266 head ref, and in that case, putting all
2268 head ref, and which are missing from the remote
2269 repository, into the remote
2272 ancestor to the local head, the push fails.
2275 </span></dt><dd>
2277 "reachable" from that commit. More
2279 another if we can reach the one from the other by a <a class="link" href="#def_chain">chain</a>
2282 <a class="link" href="#def_tree_object">trees</a> to the trees or <a class="link" href="#def_blob_object">blobs</a>
2283 that they contain.
2286 </span></dt><dd>
2289 to the result.
2292 </span></dt><dd>
2298 </span></dt><dd>
2299 A reflog shows the local "history" of a ref. In other words,
2300 it can tell you what the 3rd last revision in <span class="emphasis"><em>this</em></span> repository
2302 yesterday 9:14pm. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> for details.
2305 </span></dt><dd>
2312 <a class="link" href="#def_branch">branch</a> <a class="link" href="#def_head">head</a> from the $URL and store
2315 master branch head as to-upstream branch at $URL". See also
2319 </span></dt><dd>
2320 A regular git <a class="link" href="#def_branch">branch</a> that is used to follow changes from
2322 branch should not contain direct modifications or have local commits
2323 made to it. A remote-tracking branch can usually be
2328 </span></dt><dd>
2332 accompanied by meta data from one or more <a class="link" href="#def_porcelain">porcelains</a>. A
2333 repository can share an object database with other repositories
2337 </span></dt><dd>
2338 The action of fixing up manually what a failed automatic
2342 </span></dt><dd>
2343 A particular state of files and directories which was stored in the
2348 </span></dt><dd>
2349 To throw away part of the development, i.e. to assign the
2350 <a class="link" href="#def_head">head</a> to an earlier <a class="link" href="#def_revision">revision</a>.
2353 </span></dt><dd>
2354 Source code management (tool).
2357 </span></dt><dd>
2361 </span></dt><dd>
2363 history some of whose <a class="link" href="#def_commit">commits</a> have <a class="link" href="#def_parent">parents</a> cauterized away (in other
2364 words, git is told to pretend that these commits do not have the
2365 parents, even though they are recorded in the <a class="link" href="#def_commit_object">commit object</a>). This is sometimes useful when you are interested only in the
2366 recent history of a project even though the real history recorded in the
2367 upstream is much larger. A shallow repository
2368 is created by giving the <code class="literal">--depth</code> option to <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a>, and
2369 its history can be later deepened with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
2372 </span></dt><dd>
2374 id itself, it is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when
2375 referenced, it recursively dereferences to this reference.
2376 <span class="emphasis"><em><a class="link" href="#def_HEAD">HEAD</a></em></span> is a prime example of a symref. Symbolic
2377 references are manipulated with the <a class="ulink" href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a>
2378 command.
2381 </span></dt><dd>
2382 A <a class="link" href="#def_ref">ref</a> pointing to a <a class="link" href="#def_tag_object">tag</a> or
2383 <a class="link" href="#def_commit_object">commit object</a>. In contrast to a <a class="link" href="#def_head">head</a>,
2385 <a class="link" href="#def_tag_object">tag objects</a>) are stored in <code class="literal">$GIT_DIR/refs/tags/</code>. A
2386 git tag has nothing to do with a Lisp tag (which would be
2388 tag is most typically used to mark a particular point in the
2392 </span></dt><dd>
2393 An <a class="link" href="#def_object">object</a> containing a <a class="link" href="#def_ref">ref</a> pointing to
2394 another object, which can contain a message just like a
2396 signature, in which case it is called a "signed tag object".
2399 </span></dt><dd>
2401 identify a conceptual line of development. Since branches are very easy
2402 and inexpensive, it is often desirable to have several small branches
2403 that each contain very well defined concepts or small incremental yet
2404 related changes.
2407 </span></dt><dd>
2408 Either a <a class="link" href="#def_working_tree">working tree</a>, or a <a class="link" href="#def_tree_object">tree object</a> together with the dependent <a class="link" href="#def_blob_object">blob</a> and tree objects
2409 (i.e. a stored representation of a working tree).
2412 </span></dt><dd>
2413 An <a class="link" href="#def_object">object</a> containing a list of file names and modes along
2414 with refs to the associated blob and/or tree objects. A
2415 <a class="link" href="#def_tree">tree</a> is equivalent to a <a class="link" href="#def_directory">directory</a>.
2418 </span></dt><dd>
2419 A <a class="link" href="#def_ref">ref</a> pointing to either a <a class="link" href="#def_commit_object">commit object</a>, a <a class="link" href="#def_tree_object">tree object</a>, or a <a class="link" href="#def_tag_object">tag object</a> pointing to a tag or commit or tree object.
2422 </span></dt><dd>
2427 </span></dt><dd>
2428 An <a class="link" href="#def_object">object</a> which is not <a class="link" href="#def_reachable">reachable</a> from a
2429 <a class="link" href="#def_branch">branch</a>, <a class="link" href="#def_tag">tag</a>, or any other reference.
2432 </span></dt><dd>
2434 question (or the branch in question is rebased onto). It is configured
2436 of <span class="emphasis"><em>A</em></span> is <span class="emphasis"><em>origin/B</em></span> sometimes we say "<span class="emphasis"><em>A</em></span> is tracking <span class="emphasis"><em>origin/B</em></span>".
2439 </span></dt><dd>
2440 The tree of actual checked out files. The working tree normally
2442 plus any local changes that you have made but not yet committed.
2443 </dd></dl></div></div><div class="appendix" title="Appendix A. Git Quick Reference"><div class="titlepage"><div><div><h2 class="title"><a name="git-quick-start"></a>Appendix A. Git Quick Reference</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><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></div><p>This is a quick summary of the major commands; the previous chapters
2444 explain how these work in more detail.</p><div class="section" title="Creating a new repository"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="quick-creating-a-new-repository"></a>Creating a new repository</h2></div></div></div><p>From a tarball:</p><div class="literallayout"><p>$ tar xzf project.tar.gz<br>
2445 $ cd project<br>
2446 $ git init<br>
2447 Initialized empty Git repository in .git/<br>
2448 $ git add .<br>
2449 $ git commit</p></div><p>From a remote repository:</p><div class="literallayout"><p>$ git clone git://example.com/pub/project.git<br>
2450 $ cd project</p></div></div><div class="section" title="Managing branches"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="managing-branches"></a>Managing branches</h2></div></div></div><div class="literallayout"><p>$ git branch # list all local branches in this repo<br>
2453 $ git branch -d new # delete branch "new"</p></div><p>Instead of basing a new branch on current HEAD (the default), use:</p><div class="literallayout"><p>$ git branch new test # branch named "test"<br>
2455 $ git branch new HEAD^ # commit before the most recent<br>
2456 $ git branch new HEAD^^ # commit before that<br>
2457 $ git branch new test~10 # ten commits before tip of branch "test"</p></div><p>Create and switch to a new branch at the same time:</p><div class="literallayout"><p>$ git checkout -b new v2.6.15</p></div><p>Update and examine branches from the repository you cloned from:</p><div class="literallayout"><p>$ git fetch # update<br>
2458 $ git branch -r # list<br>
2459 origin/master<br>
2460 origin/next<br>
2461 ...<br>
2462 $ git checkout -b masterwork origin/master</p></div><p>Fetch a branch from a different repository, and give it a new
2463 name in your repository:</p><div class="literallayout"><p>$ git fetch git://example.com/project.git theirbranch:mybranch<br>
2464 $ git fetch git://example.com/project.git v2.6.15:mybranch</p></div><p>Keep a list of repositories you work with regularly:</p><div class="literallayout"><p>$ git remote add example git://example.com/project.git<br>
2465 $ git remote # list remote repositories<br>
2466 example<br>
2467 origin<br>
2468 $ git remote show example # get details<br>
2469 * remote example<br>
2470 URL: git://example.com/project.git<br>
2471 Tracked remote branches<br>
2472 master<br>
2473 next<br>
2474 ...<br>
2475 $ git fetch example # update branches from example<br>
2476 $ git branch -r # list all remote branches</p></div></div><div class="section" title="Exploring history"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exploring-history"></a>Exploring history</h2></div></div></div><div class="literallayout"><p>$ gitk # visualize and browse history<br>
2477 $ git log # list all commits<br>
2478 $ git log src/ # ...modifying src/<br>
2480 $ git log master..test # ...in branch test, not in branch master<br>
2481 $ git log test..master # ...in branch master, but not in test<br>
2482 $ git log test...master # ...in one branch, not in both<br>
2485 $ git log -p # show patches as well<br>
2486 $ git show # most recent commit<br>
2491 $ git show v2.6.15:a.txt # look at old version of a.txt</p></div><p>Search for regressions:</p><div class="literallayout"><p>$ git bisect start<br>
2492 $ git bisect bad # current version is bad<br>
2495 # test here, then:<br>
2496 $ git bisect good # if this revision is good, or<br>
2497 $ git bisect bad # if this revision is bad.<br>
2498 # repeat until done.</p></div></div><div class="section" title="Making changes"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="making-changes"></a>Making changes</h2></div></div></div><p>Make sure git knows who to blame:</p><div class="literallayout"><p>$ cat >>~/.gitconfig <<\EOF<br>
2499 [user]<br>
2500 name = Your Name Comes Here<br>
2501 email = you@yourdomain.example.com<br>
2502 EOF</p></div><p>Select file contents to include in the next commit, then make the
2504 $ git add b.txt # new file<br>
2505 $ git rm c.txt # old file<br>
2506 $ git commit</p></div><p>Or, prepare and create the commit in one step:</p><div class="literallayout"><p>$ git commit d.txt # use latest content only of d.txt<br>
2507 $ git commit -a # use latest content of all tracked files</p></div></div><div class="section" title="Merging"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging"></a>Merging</h2></div></div></div><div class="literallayout"><p>$ git merge test # merge branch "test" into the current branch<br>
2508 $ git pull git://example.com/project.git master<br>
2509 # fetch and merge in remote branch<br>
2510 $ git pull . test # equivalent to git merge test</p></div></div><div class="section" title="Sharing your changes"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-your-changes"></a>Sharing your changes</h2></div></div></div><p>Importing or exporting patches:</p><div class="literallayout"><p>$ git format-patch origin..HEAD # format a patch for each commit<br>
2511 # in HEAD but not in origin<br>
2512 $ git am mbox # import patches from the mailbox "mbox"</p></div><p>Fetch a branch in a different git repository, then merge into the
2513 current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch</p></div><p>Store the fetched branch into a local branch before merging into the
2514 current branch:</p><div class="literallayout"><p>$ git pull git://example.com/project.git theirbranch:mybranch</p></div><p>After creating commits on a local branch, update the remote
2515 branch with your commits:</p><div class="literallayout"><p>$ git push ssh://example.com/project.git mybranch:theirbranch</p></div><p>When remote and local branch are both named "test":</p><div class="literallayout"><p>$ git push ssh://example.com/project.git test</p></div><p>Shortcut version for a frequently used remote repository:</p><div class="literallayout"><p>$ git remote add example ssh://example.com/project.git<br>
2516 $ git push example test</p></div></div><div class="section" title="Repository maintenance"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="repository-maintenance"></a>Repository maintenance</h2></div></div></div><p>Check for corruption:</p><div class="literallayout"><p>$ git fsck</p></div><p>Recompress, remove unused cruft:</p><div class="literallayout"><p>$ git gc</p></div></div></div><div class="appendix" title="Appendix B. Notes and todo list for this manual"><div class="titlepage"><div><div><h2 class="title"><a name="todo"></a>Appendix B. Notes and todo list for this manual</h2></div></div></div><p>This is a work in progress.</p><p>The basic requirements:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
2517 It must be readable in order, from beginning to end, by someone
2518 intelligent with a basic grasp of the UNIX command line, but without
2519 any special knowledge of git. If necessary, any other prerequisites
2520 should be specifically mentioned as they arise.
2522 Whenever possible, section headings should clearly describe the task
2523 they explain how to do, in language that requires no more knowledge
2524 than necessary: for example, "importing patches into a project" rather
2526 </li></ul></div><p>Think about how to create a clear chapter dependency graph that will
2527 allow people to get to important topics without necessarily reading
2528 everything in between.</p><p>Scan Documentation/ for other stuff left out; in particular:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
2529 howto’s
2531 some of technical/?
2533 hooks
2536 </li></ul></div><p>Scan email archives for other stuff left out</p><p>Scan man pages to see if any assume more background than this manual
2537 provides.</p><p>Simplify beginning by suggesting disconnected head instead of
2538 temporary branch creation?</p><p>Add more good examples. Entire sections of just cookbook examples
2539 might be a good idea; maybe make an "advanced examples" section a
2540 standard end-of-chapter section?</p><p>Include cross-references to the glossary, where appropriate.</p><p>Document shallow clones? See draft 1.5.0 release notes for some
2541 documentation.</p><p>Add a section on working with other version control systems, including
2542 CVS, Subversion, and just imports of series of release tarballs.</p><p>More details on gitweb?</p><p>Write a chapter on using plumbing and writing scripts.</p><p>Alternates, clone -reference, etc.</p><p>More on recovery from repository corruption. See:
2543 <a class="ulink" href="http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2" target="_top">http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2</a>
2544 <a class="ulink" href="http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2" target="_top">http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2</a></p></div></div></body></html>