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2 <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User Manual</title><link rel="stylesheet" type="text/css" href="docbook-xsl.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="id-1"></a>Git User Manual</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#_introduction">Introduction</a></span></dt><dt><span class="chapter"><a href="#repositories-and-branches">1. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#exploring-git-history">2. Exploring Git history</a></span></dt><dd><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#Developing-With-git">3. Developing with Git</a></span></dt><dd><dl><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#sharing-development">4. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">5. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#advanced-branch-management">6. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote-tracking branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#git-concepts">7. Git concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How Git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></dd><dt><span class="chapter"><a href="#submodules">8. Submodules</a></span></dt><dd><dl><dt><span class="section"><a href="#pitfalls-with-submodules">Pitfalls with submodules</a></span></dt></dl></dd><dt><span class="chapter"><a href="#low-level-operations">9. Low-level Git operations</a></span></dt><dd><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory → index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index → object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database → index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index → working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hacking-git">10. Hacking Git</a></span></dt><dd><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git’s source code</a></span></dt></dl></dd><dt><span class="chapter"><a href="#glossary">11. Git Glossary</a></span></dt><dd><dl><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></dd><dt><span class="appendix"><a href="#git-quick-start">A. Git Quick Reference</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></dd><dt><span class="appendix"><a href="#todo">B. Notes and todo list for this manual</a></span></dt><dd><dl><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></dd></dl></div>
4 <div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="_introduction"></a>Introduction</h1></div></div></div>
7 <p>This manual is designed to be readable by someone with basic UNIX
8 command-line skills, but no previous knowledge of Git.</p>
9 <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
10 to fetch and study a project using git—read these chapters to learn how
11 to build and test a particular version of a software project, search for
12 regressions, and so on.</p>
13 <p>People needing to do actual development will also want to read
14 <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>
16 <p>Comprehensive reference documentation is available through the man
17 pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command
18 <code class="literal">git</code> <code class="literal">clone</code> <span class="emphasis"><em><repo></em></span>, you can either use:</p>
22 <p>With the latter, you can use the manual viewer of your choice; see
24 <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,
25 without any explanation.</p>
26 <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
27 complete.</p>
28 </div>
29 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></div>
31 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository"></a>How to get a Git repository</h2></div></div></div>
33 <p>It will be useful to have a Git repository to experiment with as you
34 read this manual.</p>
35 <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
36 download a copy of an existing repository. If you don’t already have a
37 project in mind, here are some interesting examples:</p>
39 $ git clone git://git.kernel.org/pub/scm/git/git.git
40 # the Linux kernel (approx. 640MB download):
41 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git</pre>
42 <p>The initial clone may be time-consuming for a large project, but you
43 will only need to clone once.</p>
44 <p>The clone command creates a new directory named after the project
45 (<code class="literal">git</code> or <code class="literal">linux</code> in the examples above). After you cd into this
46 directory, you will see that it contains a copy of the project files,
49 about the history of the project.</p>
50 </div>
51 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-check-out"></a>How to check out a different version of a project</h2></div></div></div>
53 <p>Git is best thought of as a tool for storing the history of a collection
54 of files. It stores the history as a compressed collection of
55 interrelated snapshots of the project’s contents. In Git each such
57 <p>Those snapshots aren’t necessarily all arranged in a single line from
58 oldest to newest; instead, work may simultaneously proceed along
60 merge and diverge.</p>
61 <p>A single Git repository can track development on multiple branches. It
63 latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows
64 you the list of branch heads:</p>
66 * master</pre>
67 <p>A freshly cloned repository contains a single branch head, by default
68 named "master", with the working directory initialized to the state of
69 the project referred to by that branch head.</p>
71 references into the project’s history, and can be listed using the
74 v2.6.11
75 v2.6.11-tree
76 v2.6.12
77 v2.6.12-rc2
78 v2.6.12-rc3
79 v2.6.12-rc4
80 v2.6.12-rc5
81 v2.6.12-rc6
82 v2.6.13
83 ...</pre>
84 <p>Tags are expected to always point at the same version of a project,
85 while heads are expected to advance as development progresses.</p>
86 <p>Create a new branch head pointing to one of these versions and check it
89 <p>The working directory then reflects the contents that the project had
90 when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two
91 branches, with an asterisk marking the currently checked-out branch:</p>
93 master
94 * new</pre>
98 <p>Note that if the current branch head was your only reference to a
99 particular point in history, then resetting that branch may leave you
100 with no way to find the history it used to point to; so use this command
101 carefully.</p>
102 </div>
103 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="understanding-commits"></a>Understanding History: Commits</h2></div></div></div>
105 <p>Every change in the history of a project is represented by a commit.
106 The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the
107 current branch:</p>
109 commit 17cf781661e6d38f737f15f53ab552f1e95960d7
113 Remove duplicate getenv(DB_ENVIRONMENT) call
115 Noted by Tony Luck.
117 diff --git a/init-db.c b/init-db.c
119 --- a/init-db.c
120 +++ b/init-db.c
123 int main(int argc, char **argv)
124 {
125 - char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
126 + char *sha1_dir, *path;
127 int len, i;
130 <p>As you can see, a commit shows who made the latest change, what they
131 did, and why.</p>
133 "SHA-1 id", shown on the first line of the <code class="literal">git</code> <code class="literal">show</code> output. You can usually
134 refer to a commit by a shorter name, such as a tag or a branch name, but this
135 longer name can also be useful. Most importantly, it is a globally unique
136 name for this commit: so if you tell somebody else the object name (for
137 example in email), then you are guaranteed that name will refer to the same
138 commit in their repository that it does in yours (assuming their repository
139 has that commit at all). Since the object name is computed as a hash over the
140 contents of the commit, you are guaranteed that the commit can never change
141 without its name also changing.</p>
142 <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
143 history, including file data and directory contents, is stored in an object
144 with a name that is a hash of its contents.</p>
145 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="understanding-reachability"></a>Understanding history: commits, parents, and reachability</h3></div></div></div>
147 <p>Every commit (except the very first commit in a project) also has a
148 parent commit which shows what happened before this commit.
149 Following the chain of parents will eventually take you back to the
150 beginning of the project.</p>
151 <p>However, the commits do not form a simple list; Git allows lines of
152 development to diverge and then reconverge, and the point where two
153 lines of development reconverge is called a "merge". The commit
154 representing a merge can therefore have more than one parent, with
155 each parent representing the most recent commit on one of the lines
156 of development leading to that point.</p>
157 <p>The best way to see how this works is using the <a class="ulink" href="gitk.html" target="_top">gitk(1)</a>
158 command; running gitk now on a Git repository and looking for merge
159 commits will help understand how Git organizes history.</p>
161 if commit X is an ancestor of commit Y. Equivalently, you could say
162 that Y is a descendant of X, or that there is a chain of parents
163 leading from commit Y to commit X.</p>
164 </div>
165 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="history-diagrams"></a>Understanding history: History diagrams</h3></div></div></div>
167 <p>We will sometimes represent Git history using diagrams like the one
168 below. Commits are shown as "o", and the links between them with
169 lines drawn with - / and \. Time goes left to right:</p>
171 /
172 o--o--o <-- master
173 \
176 be replaced with another letter or number.</p>
177 </div>
178 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="what-is-a-branch"></a>Understanding history: What is a branch?</h3></div></div></div>
182 to the most recent commit on a branch. In the example above, the branch
183 head named "A" is a pointer to one particular commit, but we refer to
184 the line of three commits leading up to that point as all being part of
186 <p>However, when no confusion will result, we often just use the term
188 </div>
189 </div>
190 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manipulating-branches"></a>Manipulating branches</h2></div></div></div>
192 <p>Creating, deleting, and modifying branches is quick and easy; here’s
193 a summary of the commands:</p>
194 <div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code></span></dt><dd>
195 list all branches.
196 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
197 create a new branch named <span class="emphasis"><em><branch></em></span>, referencing the same
198 point in history as the current branch.
199 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <span class="emphasis"><em><branch></em></span> <span class="emphasis"><em><start-point></em></span></span></dt><dd>
201 <span class="emphasis"><em><start-point></em></span>, which may be specified any way you like,
202 including using a branch name or a tag name.
203 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <code class="literal">-d</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
204 delete the branch <span class="emphasis"><em><branch></em></span>; if the branch is not fully
205 merged in its upstream branch or contained in the current branch,
206 this command will fail with a warning.
207 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">branch</code> <code class="literal">-D</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
208 delete the branch <span class="emphasis"><em><branch></em></span> irrespective of its merged status.
209 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">switch</code> <span class="emphasis"><em><branch></em></span></span></dt><dd>
210 make the current branch <span class="emphasis"><em><branch></em></span>, updating the working
211 directory to reflect the version referenced by <span class="emphasis"><em><branch></em></span>.
212 </dd><dt><span class="term"><code class="literal">git</code> <code class="literal">switch</code> <code class="literal">-c</code> <span class="emphasis"><em><new></em></span> <span class="emphasis"><em><start-point></em></span></span></dt><dd>
213 create a new branch <span class="emphasis"><em><new></em></span> referencing <span class="emphasis"><em><start-point></em></span>, and
214 check it out.
215 </dd></dl></div>
217 branch. In fact, Git uses a file named <code class="literal">HEAD</code> in the .<code class="literal">git</code> directory
218 to remember which branch is current:</p>
220 ref: refs/heads/master</pre>
221 </div>
222 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="detached-head"></a>Examining an old version without creating a new branch</h2></div></div></div>
224 <p>The <code class="literal">git</code> <code class="literal">switch</code> command normally expects a branch head, but will also
225 accept an arbitrary commit when invoked with --detach; for example,
226 you can check out the commit referenced by a tag:</p>
228 Note: checking out 'v2.6.17'.
230 You are in 'detached HEAD' state. You can look around, make experimental
231 changes and commit them, and you can discard any commits you make in this
232 state without impacting any branches by performing another switch.
234 If you want to create a new branch to retain commits you create, you may
235 do so (now or later) by using -c with the switch command again. Example:
237 git switch -c new_branch_name
241 and git branch shows that you are no longer on a branch:</p>
243 427abfa28afedffadfca9dd8b067eb6d36bac53f
244 $ git branch
245 * (detached from v2.6.17)
246 master</pre>
248 <p>This is an easy way to check out a particular version without having to
249 make up a name for the new branch. You can still create a new branch
250 (or tag) for this version later if you decide to.</p>
251 </div>
252 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-remote-branches"></a>Examining branches from a remote repository</h2></div></div></div>
255 of the HEAD in the repository that you cloned from. That repository
256 may also have had other branches, though, and your local repository
257 keeps branches which track each of those remote branches, called
258 remote-tracking branches, which you
259 can view using the <code class="literal">-r</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p>
261 origin/HEAD
262 origin/html
263 origin/maint
264 origin/man
265 origin/master
266 origin/next
267 origin/seen
268 origin/todo</pre>
270 for short. The branches of this repository are called "remote
271 branches" from our point of view. The remote-tracking branches listed
272 above were created based on the remote branches at clone time and will
273 be updated by <code class="literal">git</code> <code class="literal">fetch</code> (hence <code class="literal">git</code> <code class="literal">pull</code>) and <code class="literal">git</code> <code class="literal">push</code>. See
274 <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>
275 <p>You might want to build on one of these remote-tracking branches
276 on a branch of your own, just as you would for a tag:</p>
279 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>
281 to refer to the repository that you cloned from.</p>
282 </div>
283 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div>
285 <p>Branches, remote-tracking branches, and tags are all references to
286 commits. All references are named with a slash-separated path name
288 shorthand:</p>
289 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
290 The branch <code class="literal">test</code> is short for <code class="literal">refs/heads/test</code>.
292 The tag <code class="literal">v2.6.18</code> is short for <code class="literal">refs/tags/v2.6.18</code>.
294 <code class="literal">origin/master</code> is short for <code class="literal">refs/remotes/origin/master</code>.
295 </li></ul></div>
296 <p>The full name is occasionally useful if, for example, there ever
297 exists a tag and a branch with the same name.</p>
298 <p>(Newly created refs are actually stored in the .<code class="literal">git/refs</code> directory,
299 under the path given by their name. However, for efficiency reasons
300 they may also be packed together in a single file; see
303 to just using the name of that repository. So, for example, "origin"
305 <p>For the complete list of paths which Git checks for references, and
306 the order it uses to decide which to choose when there are multiple
307 references with the same shorthand name, see the "SPECIFYING
308 REVISIONS" section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>.</p>
309 </div>
310 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-With-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div>
312 <p>After you clone a repository and commit a few changes of your own, you
313 may wish to check the original repository for updates.</p>
314 <p>The <code class="literal">git-fetch</code> command, with no arguments, will update all of the
315 remote-tracking branches to the latest version found in the original
316 repository. It will not touch any of your own branches—not even the
318 </div>
319 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-branches"></a>Fetching branches from other repositories</h2></div></div></div>
321 <p>You can also track branches from repositories other than the one you
324 $ git fetch staging
325 ...
326 From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
327 * [new branch] master -> staging/master
328 * [new branch] staging-linus -> staging/staging-linus
330 <p>New remote-tracking branches will be stored under the shorthand name
331 that you gave <code class="literal">git</code> <code class="literal">remote</code> <code class="literal">add</code>, in this case <code class="literal">staging</code>:</p>
333 origin/HEAD -> origin/master
334 origin/master
335 staging/master
336 staging/staging-linus
337 staging/staging-next</pre>
338 <p>If you run <code class="literal">git</code> <code class="literal">fetch</code> <span class="emphasis"><em><remote></em></span> later, the remote-tracking branches
340 <p>If you examine the file .<code class="literal">git/config</code>, you will see that Git has added
341 a new stanza:</p>
343 ...
344 [remote "staging"]
345 url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
346 fetch = +refs/heads/*:refs/remotes/staging/*
347 ...</pre>
348 <p>This is what causes Git to track the remote’s branches; you may modify
349 or delete these configuration options by editing .<code class="literal">git/config</code> with a
350 text editor. (See the "CONFIGURATION FILE" section of
352 </div>
353 </div>
354 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring Git history</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></div>
356 <p>Git is best thought of as a tool for storing the history of a
357 collection of files. It does this by storing compressed snapshots of
358 the contents of a file hierarchy, together with "commits" which show
359 the relationships between these snapshots.</p>
360 <p>Git provides extremely flexible and fast tools for exploring the
361 history of a project.</p>
362 <p>We start with one specialized tool that is useful for finding the
363 commit that introduced a bug into a project.</p>
364 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-bisect"></a>How to use bisect to find a regression</h2></div></div></div>
367 "master" crashes. Sometimes the best way to find the cause of such a
368 regression is to perform a brute-force search through the project’s
369 history to find the particular commit that caused the problem. The
370 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p>
372 $ git bisect good v2.6.18
373 $ git bisect bad master
374 Bisecting: 3537 revisions left to test after this
375 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</pre>
376 <p>If you run <code class="literal">git</code> <code class="literal">branch</code> at this point, you’ll see that Git has
377 temporarily moved you in "(no branch)". HEAD is now detached from any
378 branch and points directly to a commit (with commit id 65934) that
380 and see whether it crashes. Assume it does crash. Then:</p>
382 Bisecting: 1769 revisions left to test after this
384 <p>checks out an older version. Continue like this, telling Git at each
385 stage whether the version it gives you is good or bad, and notice
386 that the number of revisions left to test is cut approximately in
387 half each time.</p>
389 the guilty commit. You can then examine the commit with
390 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug
391 report with the commit id. Finally, run</p>
394 <p>Note that the version which <code class="literal">git</code> <code class="literal">bisect</code> checks out for you at each
395 point is just a suggestion, and you’re free to try a different
396 version if you think it would be a good idea. For example,
397 occasionally you may land on a commit that broke something unrelated;
398 run</p>
400 <p>which will run gitk and label the commit it chose with a marker that
401 says "bisect". Choose a safe-looking commit nearby, note its commit
402 id, and check it out with:</p>
404 <p>then test, run <code class="literal">bisect</code> <code class="literal">good</code> or <code class="literal">bisect</code> <code class="literal">bad</code> as appropriate, and
405 continue.</p>
406 <p>Instead of <code class="literal">git</code> <code class="literal">bisect</code> <code class="literal">visualize</code> and then <code class="literal">git</code> <code class="literal">reset</code> <code class="literal">--hard</code>
408 the current commit:</p>
410 <p>In this case, though, Git may not eventually be able to tell the first
411 bad one between some first skipped commits and a later bad commit.</p>
412 <p>There are also ways to automate the bisecting process if you have a
413 test script that can tell a good from a bad commit. See
414 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other <code class="literal">git</code>
416 </div>
417 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="naming-commits"></a>Naming commits</h2></div></div></div>
420 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
421 40-hexdigit object name
423 branch name: refers to the commit at the head of the given
424 branch
426 tag name: refers to the commit pointed to by the given tag
427 (we’ve seen branches and tags are special cases of
428 <a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>).
430 HEAD: refers to the head of the current branch
431 </li></ul></div>
433 <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> man page for the complete list of ways to
434 name revisions. Some examples:</p>
436 # are usually enough to specify it uniquely
437 $ git show HEAD^ # the parent of the HEAD commit
438 $ git show HEAD^^ # the grandparent
440 <p>Recall that merge commits may have more than one parent; by default,
441 <code class="literal">^</code> and <code class="literal">~</code> follow the first parent listed in the commit, but you can
442 also choose:</p>
445 <p>In addition to HEAD, there are several other special names for
446 commits:</p>
447 <p>Merges (to be discussed later), as well as operations such as
448 <code class="literal">git</code> <code class="literal">reset</code>, which change the currently checked-out commit, generally
449 set ORIG_HEAD to the value HEAD had before the current operation.</p>
450 <p>The <code class="literal">git</code> <code class="literal">fetch</code> operation always stores the head of the last fetched
451 branch in FETCH_HEAD. For example, if you run <code class="literal">git</code> <code class="literal">fetch</code> without
452 specifying a local branch as the target of the operation</p>
455 <p>When we discuss merges we’ll also see the special name MERGE_HEAD,
456 which refers to the other branch that we’re merging in to the current
457 branch.</p>
458 <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
459 occasionally useful for translating some name for a commit to the object
460 name for that commit:</p>
462 e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
463 </div>
464 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-tags"></a>Creating tags</h2></div></div></div>
466 <p>We can also create a tag to refer to a particular commit; after
467 running</p>
471 comment with the tag, and possibly sign it cryptographically, then you
472 should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page
473 for details.</p>
474 </div>
475 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="browsing-revisions"></a>Browsing revisions</h2></div></div></div>
477 <p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its
478 own, it shows all commits reachable from the parent commit; but you
479 can also make more specific requests:</p>
481 $ git log test..master # commits reachable from master but not test
482 $ git log master..test # ...reachable from test but not master
483 $ git log master...test # ...reachable from either test or master,
484 # but not both
486 $ git log Makefile # commits which modify Makefile
487 $ git log fs/ # ... which modify any file under fs/
488 $ git log -S'foo()' # commits which add or remove any file data
489 # matching the string 'foo()'</pre>
490 <p>And of course you can combine all of these; the following finds
491 commits since v2.5 which touch the <code class="literal">Makefile</code> or any file under <code class="literal">fs</code>:</p>
495 <p>See the <code class="literal">--pretty</code> option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more
496 display options.</p>
497 <p>Note that git log starts with the most recent commit and works
498 backwards through the parents; however, since Git history can contain
499 multiple independent lines of development, the particular order that
500 commits are listed in may be somewhat arbitrary.</p>
501 </div>
502 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generating-diffs"></a>Generating diffs</h2></div></div></div>
504 <p>You can generate diffs between any two versions using
507 <p>That will produce the diff between the tips of the two branches. If
508 you’d prefer to find the diff from their common ancestor to test, you
509 can use three dots instead of two:</p>
511 <p>Sometimes what you want instead is a set of patches; for this you can
514 <p>will generate a file with a patch for each commit reachable from test
515 but not from master.</p>
516 </div>
517 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="viewing-old-file-versions"></a>Viewing old file versions</h2></div></div></div>
519 <p>You can always view an old version of a file by just checking out the
520 correct revision first. But sometimes it is more convenient to be
521 able to view an old version of a single file without checking
522 anything out; this command does that:</p>
524 <p>Before the colon may be anything that names a commit, and after it
525 may be any path to a file tracked by Git.</p>
526 </div>
527 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div>
529 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="counting-commits-on-a-branch"></a>Counting the number of commits on a branch</h3></div></div></div>
531 <p>Suppose you want to know how many commits you’ve made on <code class="literal">mybranch</code>
534 <p>Alternatively, you may often see this sort of thing done with the
535 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
536 of all the given commits:</p>
538 </div>
539 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-equal-branches"></a>Check whether two branches point at the same history</h3></div></div></div>
541 <p>Suppose you want to check whether two branches point at the same point
542 in history.</p>
544 <p>will tell you whether the contents of the project are the same at the
545 two branches; in theory, however, it’s possible that the same project
546 contents could have been arrived at by two different historical
547 routes. You could compare the object names:</p>
549 e05db0fd4f31dde7005f075a84f96b360d05984b
550 $ git rev-list master
551 e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
552 <p>Or you could recall that the ... operator selects all commits
553 reachable from either one reference or the other but not
554 both; so</p>
557 </div>
558 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="finding-tagged-descendants"></a>Find first tagged version including a given fix</h3></div></div></div>
560 <p>Suppose you know that the commit e05db0fd fixed a certain problem.
561 You’d like to find the earliest tagged release that contains that
562 fix.</p>
563 <p>Of course, there may be more than one answer—if the history branched
564 after commit e05db0fd, then there could be multiple "earliest" tagged
565 releases.</p>
568 <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
569 name based on any tag it finds pointing to one of the commit’s
570 descendants:</p>
573 <p>The <a class="ulink" href="git-describe.html" target="_top">git-describe(1)</a> command does the opposite, naming the
574 revision using a tag on which the given commit is based:</p>
577 <p>but that may sometimes help you guess which tags might come after the
578 given commit.</p>
579 <p>If you just want to verify whether a given tagged version contains a
580 given commit, you could use <a class="ulink" href="git-merge-base.html" target="_top">git-merge-base(1)</a>:</p>
582 e05db0fd4f31dde7005f075a84f96b360d05984b</pre>
583 <p>The merge-base command finds a common ancestor of the given commits,
584 and always returns one or the other in the case where one is a
585 descendant of the other; so the above output shows that e05db0fd
591 <p>As yet another alternative, the <a class="ulink" href="git-show-branch.html" target="_top">git-show-branch(1)</a> command lists
592 the commits reachable from its arguments with a display on the left-hand
593 side that indicates which arguments that commit is reachable from.
594 So, if you run something like</p>
596 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
597 available
601 ...</pre>
604 available</pre>
607 </div>
608 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="showing-commits-unique-to-a-branch"></a>Showing commits unique to a given branch</h3></div></div></div>
610 <p>Suppose you would like to see all the commits reachable from the branch
611 head named <code class="literal">master</code> but not from any other head in your repository.</p>
612 <p>We can list all the heads in this repository with
615 bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
616 db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
617 a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
621 the help of the standard utilities cut and grep:</p>
623 refs/heads/core-tutorial
624 refs/heads/maint
625 refs/heads/tutorial-2
626 refs/heads/tutorial-fixes</pre>
627 <p>And then we can ask to see all the commits reachable from master
628 but not from these other heads:</p>
630 grep -v '^refs/heads/master' )</pre>
631 <p>Obviously, endless variations are possible; for example, to see all
632 commits reachable from some head but not from any tag in the repository:</p>
634 <p>(See <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for explanations of commit-selecting
636 </div>
637 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="making-a-release"></a>Creating a changelog and tarball for a software release</h3></div></div></div>
639 <p>The <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> command can create a tar or zip archive from
640 any version of a project; for example:</p>
642 <p>will use HEAD to produce a gzipped tar archive in which each filename
644 the output file extension if possible, see <a class="ulink" href="git-archive.html" target="_top">git-archive(1)</a> for
645 details.</p>
646 <p>Versions of Git older than 1.7.7 don’t know about the <code class="literal">tar.gz</code> format,
647 you’ll need to use gzip explicitly:</p>
648 <pre class="screen">$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz</pre>
649 <p>If you’re releasing a new version of a software project, you may want
650 to simultaneously make a changelog to include in the release
651 announcement.</p>
652 <p>Linus Torvalds, for example, makes new kernel releases by tagging them,
653 then running:</p>
660 echo "# git tag v$new"
661 echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
662 echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
663 echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
664 echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
666 <p>and then he just cut-and-pastes the output commands after verifying that
667 they look OK.</p>
668 </div>
669 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="Finding-commits-With-given-Content"></a>Finding commits referencing a file with given content</h3></div></div></div>
671 <p>Somebody hands you a copy of a file, and asks which commits modified a
672 file such that it contained the given content either before or after the
673 commit. You can find out with this:</p>
676 <p>Figuring out why this works is left as an exercise to the (advanced)
677 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
678 <a class="ulink" href="git-hash-object.html" target="_top">git-hash-object(1)</a> man pages may prove helpful.</p>
679 </div>
680 </div>
681 </div>
682 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="Developing-With-git"></a>Chapter 3. Developing with Git</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></div>
684 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="telling-git-your-name"></a>Telling Git your name</h2></div></div></div>
686 <p>Before creating any commits, you should introduce yourself to Git.
687 The easiest way to do so is to use <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>:</p>
689 $ git config --global user.email 'you@yourdomain.example.com'</pre>
691 home directory:</p>
693 name = Your Name Comes Here
694 email = you@yourdomain.example.com</pre>
695 <p>See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for
696 details on the configuration file. The file is plain text, so you can
697 also edit it with your favorite editor.</p>
698 </div>
699 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-a-new-repository"></a>Creating a new repository</h2></div></div></div>
703 $ cd project
704 $ git init</pre>
707 $ cd project
708 $ git init
709 $ git add . # include everything below ./ in the first commit:
710 $ git commit</pre>
711 </div>
712 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-make-a-commit"></a>How to make a commit</h2></div></div></div>
716 Making some changes to the working directory using your
717 favorite editor.
719 Telling Git about your changes.
721 Creating the commit using the content you told Git about
722 in step 2.
723 </li></ol></div>
725 times as you want: in order to keep track of what you want committed
726 at step 3, Git maintains a snapshot of the tree’s contents in a
728 <p>At the beginning, the content of the index will be identical to
729 that of the HEAD. The command <code class="literal">git</code> <code class="literal">diff</code> <code class="literal">--cached</code>, which shows
730 the difference between the HEAD and the index, should therefore
731 produce no output at that point.</p>
739 <p>always shows the difference between the HEAD and the index file—this
740 is what you’d commit if you created the commit now—and that</p>
743 <p>Note that <code class="literal">git</code> <code class="literal">add</code> always adds just the current contents of a file
744 to the index; further changes to the same file will be ignored unless
745 you run <code class="literal">git</code> <code class="literal">add</code> on the file again.</p>
748 <p>and Git will prompt you for a commit message and then create the new
749 commit. Check to make sure it looks like what you expected with</p>
753 <p>will update the index with any files that you’ve modified or removed
754 and create a commit, all in one step.</p>
755 <p>A number of commands are useful for keeping track of what you’re
756 about to commit:</p>
758 # would be committed if you ran "commit" now.
759 $ git diff # difference between the index file and your
760 # working directory; changes that would not
761 # be included if you ran "commit" now.
762 $ git diff HEAD # difference between HEAD and working tree; what
763 # would be committed if you ran "commit -a" now.
764 $ git status # a brief per-file summary of the above.</pre>
765 <p>You can also use <a class="ulink" href="git-gui.html" target="_top">git-gui(1)</a> to create commits, view changes in
766 the index and the working tree files, and individually select diff hunks
767 for inclusion in the index (by right-clicking on the diff hunk and
769 </div>
770 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-good-commit-messages"></a>Creating good commit messages</h2></div></div></div>
772 <p>Though not required, it’s a good idea to begin the commit message
773 with a single short (no more than 50 characters) line summarizing the
774 change, followed by a blank line and then a more thorough
775 description. The text up to the first blank line in a commit
776 message is treated as the commit title, and that title is used
777 throughout Git. For example, <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a> turns a
778 commit into email, and it uses the title on the Subject line and the
779 rest of the commit in the body.</p>
780 </div>
781 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ignoring-files"></a>Ignoring files</h2></div></div></div>
783 <p>A project will often generate files that you do <span class="emphasis"><em>not</em></span> want to track with Git.
784 This typically includes files generated by a build process or temporary
785 backup files made by your editor. Of course, <span class="emphasis"><em>not</em></span> tracking files with Git
786 is just a matter of <span class="emphasis"><em>not</em></span> calling <code class="literal">git</code> <code class="literal">add</code> on them. But it quickly becomes
787 annoying to have these untracked files lying around; e.g. they make
788 <code class="literal">git</code> <code class="literal">add</code> . practically useless, and they keep showing up in the output of
790 <p>You can tell Git to ignore certain files by creating a file called
791 .<code class="literal">gitignore</code> in the top level of your working directory, with contents
792 such as:</p>
794 # Ignore any file named foo.txt.
795 foo.txt
796 # Ignore (generated) html files,
797 *.html
798 # except foo.html which is maintained by hand.
799 !foo.html
800 # Ignore objects and archives.
801 *.[oa]</pre>
802 <p>See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for a detailed explanation of the syntax. You can
803 also place .gitignore files in other directories in your working tree, and they
804 will apply to those directories and their subdirectories. The .<code class="literal">gitignore</code>
805 files can be added to your repository like any other files (just run <code class="literal">git</code> <code class="literal">add</code>
806 <code class="literal">.gitignore</code> and <code class="literal">git</code> <code class="literal">commit</code>, as usual), which is convenient when the exclude
807 patterns (such as patterns matching build output files) would also make sense
808 for other users who clone your repository.</p>
809 <p>If you wish the exclude patterns to affect only certain repositories
810 (instead of every repository for a given project), you may instead put
811 them in a file in your repository named .<code class="literal">git/info/exclude</code>, or in any
813 Some Git commands can also take exclude patterns directly on the
814 command line. See <a class="ulink" href="gitignore.html" target="_top">gitignore(5)</a> for the details.</p>
815 </div>
816 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-merge"></a>How to merge</h2></div></div></div>
818 <p>You can rejoin two diverging branches of development using
821 <p>merges the development in the branch <code class="literal">branchname</code> into the current
822 branch.</p>
823 <p>A merge is made by combining the changes made in <code class="literal">branchname</code> and the
824 changes made up to the latest commit in your current branch since
825 their histories forked. The work tree is overwritten by the result of
826 the merge when this combining is done cleanly, or overwritten by a
827 half-merged results when this combining results in conflicts.
828 Therefore, if you have uncommitted changes touching the same files as
829 the ones impacted by the merge, Git will refuse to proceed. Most of
830 the time, you will want to commit your changes before you can merge,
831 and if you don’t, then <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> can take these changes
832 away while you’re doing the merge, and reapply them afterwards.</p>
833 <p>If the changes are independent enough, Git will automatically complete
834 the merge and commit the result (or reuse an existing commit in case
835 of <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>, see below). On the other hand,
836 if there are conflicts—for example, if the same file is
837 modified in two different ways in the remote branch and the local
838 branch—then you are warned; the output may look something like this:</p>
841 Auto-merged file.txt
842 CONFLICT (content): Merge conflict in file.txt
843 Automatic merge failed; fix conflicts and then commit the result.</pre>
844 <p>Conflict markers are left in the problematic files, and after
845 you resolve the conflicts manually, you can update the index
846 with the contents and run Git commit, as you normally would when
847 creating a new file.</p>
848 <p>If you examine the resulting commit using gitk, you will see that it
849 has two parents, one pointing to the top of the current branch, and
850 one to the top of the other branch.</p>
851 </div>
852 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="resolving-a-merge"></a>Resolving a merge</h2></div></div></div>
854 <p>When a merge isn’t resolved automatically, Git leaves the index and
855 the working tree in a special state that gives you all the
856 information you need to help resolve the merge.</p>
857 <p>Files with conflicts are marked specially in the index, so until you
858 resolve the problem and update the index, <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> will
859 fail:</p>
861 file.txt: needs merge</pre>
862 <p>Also, <a class="ulink" href="git-status.html" target="_top">git-status(1)</a> will list those files as "unmerged", and the
863 files with conflicts will have conflict markers added, like this:</p>
865 Hello world
866 =======
867 Goodbye
871 $ git commit</pre>
872 <p>Note that the commit message will already be filled in for you with
873 some information about the merge. Normally you can just use this
874 default message unchanged, but you may add additional commentary of
875 your own if desired.</p>
876 <p>The above is all you need to know to resolve a simple merge. But Git
877 also provides more information to help resolve conflicts:</p>
878 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="conflict-resolution"></a>Getting conflict-resolution help during a merge</h3></div></div></div>
880 <p>All of the changes that Git was able to merge automatically are
881 already added to the index file, so <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> shows only
882 the conflicts. It uses an unusual syntax:</p>
884 diff --cc file.txt
886 --- a/file.txt
887 +++ b/file.txt
889 ++<<<<<<< HEAD:file.txt
890 +Hello world
891 ++=======
892 + Goodbye
894 <p>Recall that the commit which will be committed after we resolve this
895 conflict will have two parents instead of the usual one: one parent
896 will be HEAD, the tip of the current branch; the other will be the
897 tip of the other branch, which is stored temporarily in MERGE_HEAD.</p>
898 <p>During the merge, the index holds three versions of each file. Each of
901 $ git show :2:file.txt # the version from HEAD.
903 <p>When you ask <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the conflicts, it runs a
904 three-way diff between the conflicted merge results in the work tree with
906 mixed (in other words, when a hunk’s merge results come only from stage 2,
908 <p>The diff above shows the differences between the working-tree version of
910 each line by a single <code class="literal">+</code> or <code class="literal">-</code>, it now uses two columns: the first
911 column is used for differences between the first parent and the working
912 directory copy, and the second for differences between the second parent
913 and the working directory copy. (See the "COMBINED DIFF FORMAT" section
914 of <a class="ulink" href="git-diff-files.html" target="_top">git-diff-files(1)</a> for a details of the format.)</p>
915 <p>After resolving the conflict in the obvious way (but before updating the
916 index), the diff will look like:</p>
918 diff --cc file.txt
920 --- a/file.txt
921 +++ b/file.txt
923 - Hello world
924 -Goodbye
925 ++Goodbye world</pre>
927 first parent, deleted "Goodbye" from the second parent, and added
929 <p>Some special diff options allow diffing the working directory against
930 any of these stages:</p>
932 $ git diff --base file.txt # same as the above
934 $ git diff --ours file.txt # same as the above
936 $ git diff --theirs file.txt # same as the above.</pre>
937 <p>When using the <span class="emphasis"><em>ort</em></span> merge strategy (the default), before updating the working
938 tree with the result of the merge, Git writes a ref named AUTO_MERGE
939 reflecting the state of the tree it is about to write. Conflicted paths with
940 textual conflicts that could not be automatically merged are written to this
941 tree with conflict markers, just as in the working tree. AUTO_MERGE can thus be
942 used with <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a> to show the changes you’ve made so far to resolve
943 conflicts. Using the same example as above, after resolving the conflict we
944 get:</p>
946 diff --git a/file.txt b/file.txt
948 --- a/file.txt
949 +++ b/file.txt
951 -<<<<<<< HEAD:file.txt
952 -Hello world
953 -=======
954 -Goodbye
956 +Goodbye world</pre>
957 <p>Notice that the diff shows we deleted the conflict markers and both versions of
959 <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
960 for merges:</p>
962 $ gitk --merge</pre>
963 <p>These will display all commits which exist only on HEAD or on
964 MERGE_HEAD, and which touch an unmerged file.</p>
965 <p>You may also use <a class="ulink" href="git-mergetool.html" target="_top">git-mergetool(1)</a>, which lets you merge the
966 unmerged files using external tools such as Emacs or kdiff3.</p>
970 <code class="literal">git</code> <code class="literal">diff</code> will (by default) no longer show diffs for that file.</p>
971 </div>
972 </div>
973 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="undoing-a-merge"></a>Undoing a merge</h2></div></div></div>
975 <p>If you get stuck and decide to just give up and throw the whole mess
976 away, you can always return to the pre-merge state with</p>
980 <p>However, this last command can be dangerous in some cases—never
981 throw away a commit you have already committed if that commit may
982 itself have been merged into another branch, as doing so may confuse
983 further merges.</p>
984 </div>
985 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fast-forwards"></a>Fast-forward merges</h2></div></div></div>
987 <p>There is one special case not mentioned above, which is treated
988 differently. Normally, a merge results in a merge commit, with two
989 parents, one pointing at each of the two lines of development that
990 were merged.</p>
991 <p>However, if the current branch is an ancestor of the other—so every commit
992 present in the current branch is already contained in the other branch—then Git
993 just performs a "fast-forward"; the head of the current branch is moved forward
994 to point at the head of the merged-in branch, without any new commits being
995 created.</p>
996 </div>
997 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fixing-mistakes"></a>Fixing mistakes</h2></div></div></div>
999 <p>If you’ve messed up the working tree, but haven’t yet committed your
1000 mistake, you can return the entire working tree to the last committed
1001 state with</p>
1003 <p>If you make a commit that you later wish you hadn’t, there are two
1004 fundamentally different ways to fix the problem:</p>
1006 You can create a new commit that undoes whatever was done
1007 by the old commit. This is the correct thing if your
1008 mistake has already been made public.
1010 You can go back and modify the old commit. You should
1011 never do this if you have already made the history public;
1012 Git does not normally expect the "history" of a project to
1013 change, and cannot correctly perform repeated merges from
1014 a branch that has had its history changed.
1015 </li></ol></div>
1016 <div class="section"><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>
1018 <p>Creating a new commit that reverts an earlier change is very easy;
1019 just pass the <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> command a reference to the bad
1020 commit; for example, to revert the most recent commit:</p>
1022 <p>This will create a new commit which undoes the change in HEAD. You
1023 will be given a chance to edit the commit message for the new commit.</p>
1026 <p>In this case Git will attempt to undo the old change while leaving
1027 intact any changes made since then. If more recent changes overlap
1028 with the changes to be reverted, then you will be asked to fix
1029 conflicts manually, just as in the case of <a class="link" href="#resolving-a-merge" title="Resolving a merge">resolving a merge</a>.</p>
1030 </div>
1031 <div class="section"><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>
1033 <p>If the problematic commit is the most recent commit, and you have not
1034 yet made that commit public, then you may just
1035 <a class="link" href="#undoing-a-merge" title="Undoing a merge">destroy it using <code class="literal">git</code> <code class="literal">reset</code></a>.</p>
1036 <p>Alternatively, you
1037 can edit the working directory and update the index to fix your
1038 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
1041 <p>which will replace the old commit by a new commit incorporating your
1042 changes, giving you a chance to edit the old commit message first.</p>
1043 <p>Again, you should never do this to a commit that may already have
1044 been merged into another branch; use <a class="ulink" href="git-revert.html" target="_top">git-revert(1)</a> instead in
1045 that case.</p>
1046 <p>It is also possible to replace commits further back in the history, but
1047 this is an advanced topic to be left for
1048 <a class="link" href="#cleaning-up-history" title="Chapter 5. Rewriting history and maintaining patch series">another chapter</a>.</p>
1049 </div>
1050 <div class="section"><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>
1052 <p>In the process of undoing a previous bad change, you may find it
1053 useful to check out an older version of a particular file using
1056 <p>replaces path/to/file by the contents it had in the commit HEAD^, and
1057 also updates the index to match. It does not change branches.</p>
1058 <p>If you just want to look at an old version of the file, without
1059 modifying the working directory, you can do that with
1063 </div>
1064 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="interrupted-work"></a>Temporarily setting aside work in progress</h3></div></div></div>
1066 <p>While you are in the middle of working on something complicated, you
1067 find an unrelated but obvious and trivial bug. You would like to fix it
1068 before continuing. You can use <a class="ulink" href="git-stash.html" target="_top">git-stash(1)</a> to save the current
1069 state of your work, and after fixing the bug (or, optionally after doing
1070 so on a different branch and then coming back), unstash the
1071 work-in-progress changes.</p>
1074 reset your working tree and the index to match the tip of your
1075 current branch. Then you can make your fix as usual.</p>
1078 <p>After that, you can go back to what you were working on with
1079 <code class="literal">git</code> <code class="literal">stash</code> <code class="literal">pop</code>:</p>
1081 </div>
1082 </div>
1083 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-good-performance"></a>Ensuring good performance</h2></div></div></div>
1085 <p>On large repositories, Git depends on compression to keep the history
1086 information from taking up too much space on disk or in memory. Some
1087 Git commands may automatically run <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a>, so you don’t
1088 have to worry about running it manually. However, compressing a large
1089 repository may take a while, so you may want to call <code class="literal">gc</code> explicitly
1090 to avoid automatic compression kicking in when it is not convenient.</p>
1091 </div>
1092 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ensuring-reliability"></a>Ensuring reliability</h2></div></div></div>
1094 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-corruption"></a>Checking the repository for corruption</h3></div></div></div>
1096 <p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command runs a number of self-consistency checks
1097 on the repository, and reports on any problems. This may take some
1098 time.</p>
1100 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1101 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1102 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1103 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1104 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1105 dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1106 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1107 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1108 ...</pre>
1109 <p>You will see informational messages on dangling objects. They are objects
1110 that still exist in the repository but are no longer referenced by any of
1111 your branches, and can (and will) be removed after a while with <code class="literal">gc</code>.
1112 You can run <code class="literal">git</code> <code class="literal">fsck</code> <code class="literal">--no-dangling</code> to suppress these messages, and still
1113 view real errors.</p>
1114 </div>
1115 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-lost-changes"></a>Recovering lost changes</h3></div></div></div>
1117 <div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="reflogs"></a>Reflogs</h4></div></div></div>
1119 <p>Say you modify a branch with <a class="link" href="#fixing-mistakes" title="Fixing mistakes"><code class="literal">git</code> <code class="literal">reset</code> <code class="literal">--hard</code></a>,
1120 and then realize that the branch was the only reference you had to
1121 that point in history.</p>
1123 previous values of each branch. So in this case you can still find the
1124 old history using, for example,</p>
1126 <p>This lists the commits reachable from the previous version of the
1128 that accepts a commit, not just with <code class="literal">git</code> <code class="literal">log</code>. Some other examples:</p>
1131 $ gitk master@{yesterday} # See where it pointed yesterday,
1132 $ gitk master@{"1 week ago"} # ... or last week
1133 $ git log --walk-reflogs master # show reflog entries for master</pre>
1136 <p>will show what HEAD pointed to one week ago, not what the current branch
1137 pointed to one week ago. This allows you to see the history of what
1138 you’ve checked out.</p>
1140 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
1141 how to control this pruning, and see the "SPECIFYING REVISIONS"
1142 section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> for details.</p>
1143 <p>Note that the reflog history is very different from normal Git history.
1144 While normal history is shared by every repository that works on the
1145 same project, the reflog history is not shared: it tells you only about
1146 how the branches in your local repository have changed over time.</p>
1147 </div>
1148 <div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="dangling-object-recovery"></a>Examining dangling objects</h4></div></div></div>
1150 <p>In some situations the reflog may not be able to save you. For example,
1151 suppose you delete a branch, then realize you need the history it
1152 contained. The reflog is also deleted; however, if you have not yet
1153 pruned the repository, then you may still be able to find the lost
1154 commits in the dangling objects that <code class="literal">git</code> <code class="literal">fsck</code> reports. See
1155 <a class="xref" href="#dangling-objects" title="Dangling objects">the section called “Dangling objects”</a> for the details.</p>
1157 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1158 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1159 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1160 ...</pre>
1161 <p>You can examine
1162 one of those dangling commits with, for example,</p>
1164 <p>which does what it sounds like: it says that you want to see the commit
1165 history that is described by the dangling commit(s), but not the
1166 history that is described by all your existing branches and tags. Thus
1167 you get exactly the history reachable from that commit that is lost.
1168 (And notice that it might not be just one commit: we only report the
1169 "tip of the line" as being dangling, but there might be a whole deep
1170 and complex commit history that was dropped.)</p>
1171 <p>If you decide you want the history back, you can always create a new
1172 reference pointing to it, for example, a new branch:</p>
1174 <p>Other types of dangling objects (blobs and trees) are also possible, and
1175 dangling objects can arise in other situations.</p>
1176 </div>
1177 </div>
1178 </div>
1179 </div>
1180 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="sharing-development"></a>Chapter 4. Sharing development with others</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></div>
1182 <div class="section"><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>
1184 <p>After you clone a repository and commit a few changes of your own, you
1185 may wish to check the original repository for updates and merge them
1186 into your own work.</p>
1187 <p>We have already seen <a class="link" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">how to
1188 keep remote-tracking branches up to date</a> with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>,
1189 and how to merge two branches. So you can merge in changes from the
1190 original repository’s master branch with:</p>
1192 $ git merge origin/master</pre>
1193 <p>However, the <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a> command provides a way to do this in
1194 one step:</p>
1196 <p>In fact, if you have <code class="literal">master</code> checked out, then this branch has been
1197 configured by <code class="literal">git</code> <code class="literal">clone</code> to get changes from the HEAD branch of the
1198 origin repository. So often you can
1199 accomplish the above with just a simple</p>
1201 <p>This command will fetch changes from the remote branches to your
1202 remote-tracking branches <code class="literal">origin/</code>*, and merge the default branch into
1203 the current branch.</p>
1204 <p>More generally, a branch that is created from a remote-tracking branch
1205 will pull
1206 by default from that branch. See the descriptions of the
1207 <code class="literal">branch.</code><span class="emphasis"><em><name></em></span><code class="literal">.remote</code> and <code class="literal">branch.</code><span class="emphasis"><em><name></em></span><code class="literal">.merge</code> options in
1208 <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
1209 <a class="ulink" href="git-checkout.html" target="_top">git-checkout(1)</a>, to learn how to control these defaults.</p>
1210 <p>In addition to saving you keystrokes, <code class="literal">git</code> <code class="literal">pull</code> also helps you by
1211 producing a default commit message documenting the branch and
1212 repository that you pulled from.</p>
1213 <p>(But note that no such commit will be created in the case of a
1214 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; instead, your branch will just be
1215 updated to point to the latest commit from the upstream branch.)</p>
1216 <p>The <code class="literal">git</code> <code class="literal">pull</code> command can also be given . as the "remote" repository,
1217 in which case it just merges in a branch from the current repository; so
1218 the commands</p>
1220 $ git merge branch</pre>
1222 </div>
1223 <div class="section"><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>
1225 <p>If you just have a few changes, the simplest way to submit them may
1226 just be to send them as patches in email:</p>
1227 <p>First, use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>; for example:</p>
1229 <p>will produce a numbered series of files in the current directory, one
1231 <p><code class="literal">git</code> <code class="literal">format-patch</code> can include an initial "cover letter". You can insert
1232 commentary on individual patches after the three dash line which
1234 itself. If you use <code class="literal">git</code> <code class="literal">notes</code> to track your cover letter material,
1235 <code class="literal">git</code> <code class="literal">format-patch</code> <code class="literal">--notes</code> will include the commit’s notes in a similar
1236 manner.</p>
1237 <p>You can then import these into your mail client and send them by
1238 hand. However, if you have a lot to send at once, you may prefer to
1239 use the <a class="ulink" href="git-send-email.html" target="_top">git-send-email(1)</a> script to automate the process.
1240 Consult the mailing list for your project first to determine
1241 their requirements for submitting patches.</p>
1242 </div>
1243 <div class="section"><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>
1245 <p>Git also provides a tool called <a class="ulink" href="git-am.html" target="_top">git-am(1)</a> (am stands for
1246 "apply mailbox"), for importing such an emailed series of patches.
1247 Just save all of the patch-containing messages, in order, into a
1250 <p>Git will apply each patch in order; if any conflicts are found, it
1251 will stop, and you can fix the conflicts as described in
1252 "<a class="link" href="#resolving-a-merge" title="Resolving a merge">Resolving a merge</a>". (The <code class="literal">-3</code> option tells
1253 Git to perform a merge; if you would prefer it just to abort and
1254 leave your tree and index untouched, you may omit that option.)</p>
1255 <p>Once the index is updated with the results of the conflict
1256 resolution, instead of creating a new commit, just run</p>
1258 <p>and Git will create the commit for you and continue applying the
1259 remaining patches from the mailbox.</p>
1260 <p>The final result will be a series of commits, one for each patch in
1261 the original mailbox, with authorship and commit log message each
1262 taken from the message containing each patch.</p>
1263 </div>
1264 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="public-repositories"></a>Public Git repositories</h2></div></div></div>
1266 <p>Another way to submit changes to a project is to tell the maintainer
1267 of that project to pull the changes from your repository using
1268 <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</code> <code class="literal">pull</code></a>" we described this as a way to get
1269 updates from the "main" repository, but it works just as well in the
1270 other direction.</p>
1271 <p>If you and the maintainer both have accounts on the same machine, then
1272 you can just pull changes from each other’s repositories directly;
1273 commands that accept repository URLs as arguments will also accept a
1274 local directory name:</p>
1276 $ git pull /path/to/other/repository</pre>
1279 <p>For projects with few developers, or for synchronizing a few private
1280 repositories, this may be all you need.</p>
1281 <p>However, the more common way to do this is to maintain a separate public
1282 repository (usually on a different host) for others to pull changes
1283 from. This is usually more convenient, and allows you to cleanly
1284 separate private work in progress from publicly visible work.</p>
1285 <p>You will continue to do your day-to-day work in your personal
1286 repository, but periodically "push" changes from your personal
1287 repository into your public repository, allowing other developers to
1288 pull from that repository. So the flow of changes, in a situation
1289 where there is one other developer with a public repository, looks
1290 like this:</p>
1292 your personal repo ------------------> your public repo
1293 ^ |
1294 | |
1295 | you pull | they pull
1296 | |
1297 | |
1298 | they push V
1301 <div class="section"><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>
1304 first create a new clone of the repository and tell <code class="literal">git</code> <code class="literal">daemon</code> that it
1305 is meant to be public:</p>
1307 $ touch proj.git/git-daemon-export-ok</pre>
1309 just the contents of the .<code class="literal">git</code> directory, without any files checked out
1310 around it.</p>
1312 public repository. You can use scp, rsync, or whatever is most
1313 convenient.</p>
1314 </div>
1315 <div class="section"><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>
1318 <p>If someone else administers the server, they should tell you what
1320 appear at. You can then skip to the section
1321 "<a class="link" href="#pushing-changes-to-a-public-repository" title="Pushing changes to a public repository">Pushing changes to a public
1323 <p>Otherwise, all you need to do is start <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a>; it will
1324 listen on port 9418. By default, it will allow access to any directory
1325 that looks like a Git directory and contains the magic file
1326 git-daemon-export-ok. Passing some directory paths as <code class="literal">git</code> <code class="literal">daemon</code>
1327 arguments will further restrict the exports to those paths.</p>
1328 <p>You can also run <code class="literal">git</code> <code class="literal">daemon</code> as an inetd service; see the
1329 <a class="ulink" href="git-daemon.html" target="_top">git-daemon(1)</a> man page for details. (See especially the
1330 examples section.)</p>
1331 </div>
1332 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="exporting-via-http"></a>Exporting a git repository via HTTP</h3></div></div></div>
1334 <p>The Git protocol gives better performance and reliability, but on a
1335 host with a web server set up, HTTP exports may be simpler to set up.</p>
1336 <p>All you need to do is place the newly created bare Git repository in
1337 a directory that is exported by the web server, and make some
1338 adjustments to give web clients some extra information they need:</p>
1340 $ cd proj.git
1341 $ git --bare update-server-info
1342 $ mv hooks/post-update.sample hooks/post-update</pre>
1343 <p>(For an explanation of the last two lines, see
1344 <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>
1345 <p>Advertise the URL of <code class="literal">proj.git</code>. Anybody else should then be able to
1346 clone or pull from that URL, for example with a command line like:</p>
1348 <p>(See also
1349 <a class="ulink" href="howto/setup-git-server-over-http.html" target="_top">setup-git-server-over-http</a>
1350 for a slightly more sophisticated setup using WebDAV which also
1351 allows pushing over HTTP.)</p>
1352 </div>
1353 <div class="section"><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>
1355 <p>Note that the two techniques outlined above (exporting via
1356 <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
1357 maintainers to fetch your latest changes, but they do not allow write
1358 access, which you will need to update the public repository with the
1359 latest changes created in your private repository.</p>
1360 <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
1361 update the remote branch named <code class="literal">master</code> with the latest state of your
1366 <p>As with <code class="literal">git</code> <code class="literal">fetch</code>, <code class="literal">git</code> <code class="literal">push</code> will complain if this does not result in a
1367 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>; see the following section for details on
1368 handling this case.</p>
1371 repository that has a checked-out working tree, but a push to update the
1372 currently checked-out branch is denied by default to prevent confusion.
1373 See the description of the receive.denyCurrentBranch option
1375 <p>As with <code class="literal">git</code> <code class="literal">fetch</code>, you may also set up configuration options to
1376 save typing; so, for example:</p>
1380 url = yourserver.com:proj.git
1381 fetch = +refs/heads/*:refs/remotes/example/*</pre>
1384 <p>See the explanations of the <code class="literal">remote.</code><span class="emphasis"><em><name></em></span><code class="literal">.url</code>,
1385 <code class="literal">branch.</code><span class="emphasis"><em><name></em></span><code class="literal">.remote</code>, and <code class="literal">remote.</code><span class="emphasis"><em><name></em></span><code class="literal">.push</code> options in
1387 </div>
1388 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="forcing-push"></a>What to do when a push fails</h3></div></div></div>
1390 <p>If a push would not result in a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> of the
1391 remote branch, then it will fail with an error like:</p>
1393 error: failed to push some refs to '...'
1394 hint: Updates were rejected because the tip of your current branch is behind
1395 hint: its remote counterpart. Integrate the remote changes (e.g.
1396 hint: 'git pull ...') before pushing again.
1397 hint: See the 'Note about fast-forwards' in 'git push --help' for details.</pre>
1399 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1400 use <code class="literal">git</code> <code class="literal">reset</code> <code class="literal">--hard</code> to remove already-published commits, or
1402 use <code class="literal">git</code> <code class="literal">commit</code> <code class="literal">--amend</code> to replace already-published commits
1403 (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
1405 use <code class="literal">git</code> <code class="literal">rebase</code> to rebase any already-published commits (as
1406 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>).
1407 </li></ul></div>
1408 <p>You may force <code class="literal">git</code> <code class="literal">push</code> to perform the update anyway by preceding the
1409 branch name with a plus sign:</p>
1411 <p>Note the addition of the <code class="literal">+</code> sign. Alternatively, you can use the
1414 <p>Normally whenever a branch head in a public repository is modified, it
1415 is modified to point to a descendant of the commit that it pointed to
1416 before. By forcing a push in this situation, you break that convention.
1417 (See <a class="xref" href="#problems-With-rewriting-history" title="Problems with rewriting history">the section called “Problems with rewriting history”</a>.)</p>
1418 <p>Nevertheless, this is a common practice for people that need a simple
1419 way to publish a work-in-progress patch series, and it is an acceptable
1420 compromise as long as you warn other developers that this is how you
1421 intend to manage the branch.</p>
1422 <p>It’s also possible for a push to fail in this way when other people have
1423 the right to push to the same repository. In that case, the correct
1424 solution is to retry the push after first updating your work: either by a
1425 pull, or by a fetch followed by a rebase; see the
1426 <a class="link" href="#setting-up-a-shared-repository" title="Setting up a shared repository">next section</a> and
1427 <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for more.</p>
1428 </div>
1429 <div class="section"><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>
1431 <p>Another way to collaborate is by using a model similar to that
1432 commonly used in CVS, where several developers with special rights
1433 all push to and pull from a single shared repository. See
1434 <a class="ulink" href="gitcvs-migration.html" target="_top">gitcvs-migration(7)</a> for instructions on how to
1435 set this up.</p>
1436 <p>However, while there is nothing wrong with Git’s support for shared
1437 repositories, this mode of operation is not generally recommended,
1438 simply because the mode of collaboration that Git supports—by
1439 exchanging patches and pulling from public repositories—has so many
1440 advantages over the central shared repository:</p>
1441 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1442 Git’s ability to quickly import and merge patches allows a
1443 single maintainer to process incoming changes even at very
1444 high rates. And when that becomes too much, <code class="literal">git</code> <code class="literal">pull</code> provides
1445 an easy way for that maintainer to delegate this job to other
1446 maintainers while still allowing optional review of incoming
1447 changes.
1449 Since every developer’s repository has the same complete copy
1450 of the project history, no repository is special, and it is
1451 trivial for another developer to take over maintenance of a
1452 project, either by mutual agreement, or because a maintainer
1453 becomes unresponsive or difficult to work with.
1455 The lack of a central group of "committers" means there is
1456 less need for formal decisions about who is "in" and who is
1457 "out".
1458 </li></ul></div>
1459 </div>
1460 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="setting-up-gitweb"></a>Allowing web browsing of a repository</h3></div></div></div>
1462 <p>The gitweb cgi script provides users an easy way to browse your
1463 project’s revisions, file contents and logs without having to install
1464 Git. Features like RSS/Atom feeds and blame/annotation details may
1465 optionally be enabled.</p>
1466 <p>The <a class="ulink" href="git-instaweb.html" target="_top">git-instaweb(1)</a> command provides a simple way to start
1467 browsing the repository using gitweb. The default server when using
1468 instaweb is lighttpd.</p>
1469 <p>See the file gitweb/INSTALL in the Git source tree and
1470 <a class="ulink" href="gitweb.html" target="_top">gitweb(1)</a> for instructions on details setting up a permanent
1471 installation with a CGI or Perl capable server.</p>
1472 </div>
1473 </div>
1474 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository-with-minimal-history"></a>How to get a Git repository with minimal history</h2></div></div></div>
1477 history, is useful when one is interested only in recent history
1478 of a project and getting full history from the upstream is
1479 expensive.</p>
1481 the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> <code class="literal">--depth</code> switch. The depth can later be
1482 changed with the <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> <code class="literal">--depth</code> switch, or full
1484 <p>Merging inside a <a class="link" href="#def_shallow_clone">shallow clone</a> will work as long
1485 as a merge base is in the recent history.
1486 Otherwise, it will be like merging unrelated histories and may
1487 have to result in huge conflicts. This limitation may make such
1488 a repository unsuitable to be used in merge based workflows.</p>
1489 </div>
1490 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-development-examples"></a>Examples</h2></div></div></div>
1492 <div class="section"><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>
1494 <p>This describes how Tony Luck uses Git in his role as maintainer of the
1495 IA64 architecture for the Linux kernel.</p>
1497 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
1498 A "test" tree into which patches are initially placed so that they
1499 can get some exposure when integrated with other ongoing development.
1500 This tree is available to Andrew for pulling into -mm whenever he
1501 wants.
1503 A "release" tree into which tested patches are moved for final sanity
1504 checking, and as a vehicle to send them upstream to Linus (by sending
1505 him a "please pull" request.)
1506 </li></ul></div>
1508 containing a logical grouping of patches.</p>
1509 <p>To set this up, first create your work tree by cloning Linus’s public
1510 tree:</p>
1511 <pre class="screen">$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git work
1512 $ cd work</pre>
1513 <p>Linus’s tree will be stored in the remote-tracking branch named origin/master,
1514 and can be updated using <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>; you can track other
1515 public trees using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a> to set up a "remote" and
1516 <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> to keep them up to date; see
1517 <a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a>.</p>
1518 <p>Now create the branches in which you are going to work; these start out
1519 at the current tip of origin/master branch, and should be set up (using
1520 the <code class="literal">--track</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>) to merge changes in from
1521 Linus by default.</p>
1523 $ git branch --track release origin/master</pre>
1524 <p>These can be easily kept up to date using <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.</p>
1527 <p>Important note! If you have any local changes in these branches, then
1528 this merge will create a commit object in the history (with no local
1529 changes Git will simply do a "fast-forward" merge). Many people dislike
1530 the "noise" that this creates in the Linux history, so you should avoid
1531 doing this capriciously in the <code class="literal">release</code> branch, as these noisy commits
1532 will become part of the permanent history when you ask Linus to pull
1533 from the release branch.</p>
1534 <p>A few configuration variables (see <a class="ulink" href="git-config.html" target="_top">git-config(1)</a>) can
1535 make it easy to push both branches to your public tree. (See
1536 <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>
1538 [remote "mytree"]
1539 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux.git
1540 push = release
1541 push = test
1542 EOF</pre>
1543 <p>Then you can push both the test and release trees using
1550 <p>Now to apply some patches from the community. Think of a short
1551 snappy name for a branch to hold this patch (or related group of
1552 patches), and create a new branch from a recent stable tag of
1553 Linus’s branch. Picking a stable base for your branch will:
1554 1) help you: by avoiding inclusion of unrelated and perhaps lightly
1555 tested changes
1556 2) help future bug hunters that use <code class="literal">git</code> <code class="literal">bisect</code> to find problems</p>
1558 <p>Now you apply the patch(es), run some tests, and commit the change(s). If
1559 the patch is a multi-part series, then you should apply each as a separate
1560 commit to this branch.</p>
1562 <p>When you are happy with the state of this change, you can merge it into the
1565 <p>It is unlikely that you would have any conflicts here … but you might if you
1566 spent a while on this step and had also pulled new versions from upstream.</p>
1567 <p>Sometime later when enough time has passed and testing done, you can pull the
1568 same branch into the <code class="literal">release</code> tree ready to go upstream. This is where you
1569 see the value of keeping each patch (or patch series) in its own branch. It
1570 means that the patches can be moved into the <code class="literal">release</code> tree in any order.</p>
1572 <p>After a while, you will have a number of branches, and despite the
1573 well chosen names you picked for each of them, you may forget what
1574 they are for, or what status they are in. To get a reminder of what
1575 changes are in a specific branch, use:</p>
1577 <p>To see whether it has already been merged into the test or release branches,
1578 use:</p>
1582 <p>(If this branch has not yet been merged, you will see some log entries.
1583 If it has been merged, then there will be no output.)</p>
1584 <p>Once a patch completes the great cycle (moving from test to release,
1585 then pulled by Linus, and finally coming back into your local
1586 <code class="literal">origin/master</code> branch), the branch for this change is no longer needed.
1587 You detect this when the output from:</p>
1591 <p>Some changes are so trivial that it is not necessary to create a separate
1592 branch and then merge into each of the test and release branches. For
1593 these changes, just apply directly to the <code class="literal">release</code> branch, and then
1596 <a class="ulink" href="git-request-pull.html" target="_top">git-request-pull(1)</a> to prepare a "please pull" request message
1597 to send to Linus:</p>
1599 $ git request-pull origin mytree release</pre>
1602 # Update a branch in my Git tree. If the branch to be updated
1603 # is origin, then pull from kernel.org. Otherwise merge
1604 # origin/master branch into test|release branch
1606 case "$1" in
1607 test|release)
1609 ;;
1610 origin)
1611 before=$(git rev-parse refs/remotes/origin/master)
1612 git fetch origin
1613 after=$(git rev-parse refs/remotes/origin/master)
1614 if [ $before != $after ]
1615 then
1616 git log $before..$after | git shortlog
1617 fi
1618 ;;
1619 *)
1621 exit 1
1622 ;;
1623 esac</pre>
1625 # Merge a branch into either the test or release branch
1627 pname=$0
1629 usage()
1630 {
1632 exit 1
1633 }
1635 git show-ref -q --verify -- refs/heads/"$1" || {
1637 usage
1638 }
1640 case "$2" in
1641 test|release)
1643 then
1645 exit 1
1646 fi
1648 ;;
1649 *)
1650 usage
1651 ;;
1652 esac</pre>
1654 # report on status of my ia64 Git tree
1656 gb=$(tput setab 2)
1657 rb=$(tput setab 1)
1658 restore=$(tput setab 9)
1660 if [ `git rev-list test..release | wc -c` -gt 0 ]
1661 then
1662 echo $rb Warning: commits in release that are not in test $restore
1663 git log test..release
1664 fi
1666 for branch in `git show-ref --heads | sed 's|^.*/||'`
1667 do
1668 if [ $branch = test -o $branch = release ]
1669 then
1670 continue
1671 fi
1673 echo -n $gb ======= $branch ====== $restore " "
1674 status=
1675 for ref in test release origin/master
1676 do
1677 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
1678 then
1680 fi
1681 done
1682 case $status in
1683 trl)
1684 echo $rb Need to pull into test $restore
1685 ;;
1686 rl)
1687 echo "In test"
1688 ;;
1689 l)
1690 echo "Waiting for linus"
1691 ;;
1692 "")
1693 echo $rb All done $restore
1694 ;;
1695 *)
1696 echo $rb "<$status>" $restore
1697 ;;
1698 esac
1699 git log origin/master..$branch | git shortlog
1700 done</pre>
1701 </div>
1702 </div>
1703 </div>
1704 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="cleaning-up-history"></a>Chapter 5. Rewriting history and maintaining patch series</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></div>
1706 <p>Normally commits are only added to a project, never taken away or
1707 replaced. Git is designed with this assumption, and violating it will
1708 cause Git’s merge machinery (for example) to do the wrong thing.</p>
1709 <p>However, there is a situation in which it can be useful to violate this
1710 assumption.</p>
1711 <div class="section"><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>
1713 <p>Suppose you are a contributor to a large project, and you want to add a
1714 complicated feature, and to present it to the other developers in a way
1715 that makes it easy for them to read your changes, verify that they are
1716 correct, and understand why you made each change.</p>
1717 <p>If you present all of your changes as a single patch (or commit), they
1718 may find that it is too much to digest all at once.</p>
1719 <p>If you present them with the entire history of your work, complete with
1720 mistakes, corrections, and dead ends, they may be overwhelmed.</p>
1723 Each patch can be applied in order.
1725 Each patch includes a single logical change, together with a
1726 message explaining the change.
1728 No patch introduces a regression: after applying any initial
1729 part of the series, the resulting project still compiles and
1730 works, and has no bugs that it didn’t have before.
1732 The complete series produces the same end result as your own
1733 (probably much messier!) development process did.
1734 </li></ol></div>
1735 <p>We will introduce some tools that can help you do this, explain how to
1736 use them, and then explain some of the problems that can arise because
1737 you are rewriting history.</p>
1738 </div>
1739 <div class="section"><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>
1741 <p>Suppose that you create a branch <code class="literal">mywork</code> on a remote-tracking branch
1744 $ vi file.txt
1745 $ git commit
1746 $ vi otherfile.txt
1747 $ git commit
1748 ...</pre>
1749 <p>You have performed no merges into mywork, so it is just a simple linear
1752 \
1754 <p>Some more interesting work has been done in the upstream project, and
1757 \
1759 <p>At this point, you could use <code class="literal">pull</code> to merge your changes back in;
1760 the result would create a new merge commit, like this:</p>
1762 \ \
1764 <p>However, if you prefer to keep the history in mywork a simple series of
1765 commits without any merges, you may instead choose to use
1768 $ git rebase origin</pre>
1769 <p>This will remove each of your commits from mywork, temporarily saving
1770 them as patches (in a directory named .<code class="literal">git/rebase-apply</code>), update mywork to
1771 point at the latest version of origin, then apply each of the saved
1772 patches to the new mywork. The result will look like:</p>
1774 \
1776 <p>In the process, it may discover conflicts. In that case it will stop
1777 and allow you to fix the conflicts; after fixing conflicts, use <code class="literal">git</code> <code class="literal">add</code>
1778 to update the index with those contents, and then, instead of
1782 <p>At any point you may use the <code class="literal">--abort</code> option to abort this process and
1783 return mywork to the state it had before you started the rebase:</p>
1785 <p>If you need to reorder or edit a number of commits in a branch, it may
1786 be easier to use <code class="literal">git</code> <code class="literal">rebase</code> <code class="literal">-i</code>, which allows you to reorder and
1787 squash commits, as well as marking them for individual editing during
1788 the rebase. See <a class="xref" href="#interactive-rebase" title="Using interactive rebases">the section called “Using interactive rebases”</a> for details, and
1789 <a class="xref" href="#reordering-patch-series" title="Reordering or selecting from a patch series">the section called “Reordering or selecting from a patch series”</a> for alternatives.</p>
1790 </div>
1791 <div class="section"><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>
1793 <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
1794 most recent commit using</p>
1796 <p>which will replace the old commit by a new commit incorporating your
1797 changes, giving you a chance to edit the old commit message first.
1798 This is useful for fixing typos in your last commit, or for adjusting
1799 the patch contents of a poorly staged commit.</p>
1800 <p>If you need to amend commits from deeper in your history, you can
1801 use <a class="link" href="#interactive-rebase" title="Using interactive rebases">interactive rebase’s <code class="literal">edit</code> instruction</a>.</p>
1802 </div>
1803 <div class="section"><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>
1805 <p>Sometimes you want to edit a commit deeper in your history. One
1806 approach is to use <code class="literal">git</code> <code class="literal">format-patch</code> to create a series of patches
1807 and then reset the state to before the patches:</p>
1809 $ git reset --hard origin</pre>
1810 <p>Then modify, reorder, or eliminate patches as needed before applying
1813 </div>
1814 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="interactive-rebase"></a>Using interactive rebases</h2></div></div></div>
1816 <p>You can also edit a patch series with an interactive rebase. This is
1817 the same as <a class="link" href="#reordering-patch-series" title="Reordering or selecting from a patch series">reordering a patch series using
1819 <p>Rebase your current HEAD on the last commit you want to retain as-is.
1822 <p>This will open your editor with a list of steps to be taken to perform
1823 your rebase.</p>
1825 pick fa1afe1 The oneline of the next commit
1826 ...
1828 # Rebase c0ffeee..deadbee onto c0ffeee
1829 #
1830 # Commands:
1831 # p, pick = use commit
1832 # r, reword = use commit, but edit the commit message
1833 # e, edit = use commit, but stop for amending
1834 # s, squash = use commit, but meld into previous commit
1835 # f, fixup = like "squash", but discard this commit's log message
1836 # x, exec = run command (the rest of the line) using shell
1837 #
1838 # These lines can be re-ordered; they are executed from top to bottom.
1839 #
1840 # If you remove a line here THAT COMMIT WILL BE LOST.
1841 #
1842 # However, if you remove everything, the rebase will be aborted.
1843 #
1844 # Note that empty commits are commented out</pre>
1845 <p>As explained in the comments, you can reorder commits, squash them
1846 together, edit commit messages, etc. by editing the list. Once you
1847 are satisfied, save the list and close your editor, and the rebase
1848 will begin.</p>
1849 <p>The rebase will stop where <code class="literal">pick</code> has been replaced with <code class="literal">edit</code> or
1850 when a step in the list fails to mechanically resolve conflicts and
1851 needs your help. When you are done editing and/or resolving conflicts
1852 you can continue with <code class="literal">git</code> <code class="literal">rebase</code> <code class="literal">--continue</code>. If you decide that
1853 things are getting too hairy, you can always bail out with <code class="literal">git</code> <code class="literal">rebase</code>
1855 the original branch by using the <a class="link" href="#reflogs" title="Reflogs">reflog</a>.</p>
1856 <p>For a more detailed discussion of the procedure and additional tips,
1857 see the "INTERACTIVE MODE" section of <a class="ulink" href="git-rebase.html" target="_top">git-rebase(1)</a>.</p>
1858 </div>
1859 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="patch-series-tools"></a>Other tools</h2></div></div></div>
1861 <p>There are numerous other tools, such as StGit, which exist for the
1862 purpose of maintaining a patch series. These are outside of the scope of
1863 this manual.</p>
1864 </div>
1865 <div class="section"><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>
1867 <p>The primary problem with rewriting the history of a branch has to do
1868 with merging. Suppose somebody fetches your branch and merges it into
1869 their branch, with a result something like this:</p>
1871 \ \
1875 /
1877 <p>If we examined all this history together in one repository, it will
1878 look like:</p>
1880 /
1881 o--o--O--o--o--o <-- old head of origin
1882 \ \
1884 <p>Git has no way of knowing that the new head is an updated version of
1885 the old head; it treats this situation exactly the same as it would if
1886 two developers had independently done the work on the old and new heads
1887 in parallel. At this point, if someone attempts to merge the new head
1888 in to their branch, Git will attempt to merge together the two (old and
1889 new) lines of development, instead of trying to replace the old by the
1890 new. The results are likely to be unexpected.</p>
1891 <p>You may still choose to publish branches whose history is rewritten,
1892 and it may be useful for others to be able to fetch those branches in
1893 order to examine or test them, but they should not attempt to pull such
1894 branches into their own work.</p>
1895 <p>For true distributed development that supports proper merging,
1896 published branches should never be rewritten.</p>
1897 </div>
1898 <div class="section"><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>
1900 <p>The <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command correctly handles history that
1901 includes merge commits. However, when the commit that it finds is a
1902 merge commit, the user may need to work harder than usual to figure out
1903 why that commit introduced a problem.</p>
1906 \ /
1907 o---o---Y---...---o---B</pre>
1908 <p>Suppose that on the upper line of development, the meaning of one
1909 of the functions that exists at Z is changed at commit X. The
1910 commits from Z leading to A change both the function’s
1911 implementation and all calling sites that exist at Z, as well
1912 as new calling sites they add, to be consistent. There is no
1913 bug at A.</p>
1914 <p>Suppose that in the meantime on the lower line of development somebody
1915 adds a new calling site for that function at commit Y. The
1916 commits from Z leading to B all assume the old semantics of that
1917 function and the callers and the callee are consistent with each
1918 other. There is no bug at B, either.</p>
1919 <p>Suppose further that the two development lines merge cleanly at C,
1920 so no conflict resolution is required.</p>
1921 <p>Nevertheless, the code at C is broken, because the callers added
1922 on the lower line of development have not been converted to the new
1923 semantics introduced on the upper line of development. So if all
1924 you know is that D is bad, that Z is good, and that
1925 <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> identifies C as the culprit, how will you
1926 figure out that the problem is due to this change in semantics?</p>
1927 <p>When the result of a <code class="literal">git</code> <code class="literal">bisect</code> is a non-merge commit, you should
1928 normally be able to discover the problem by examining just that commit.
1929 Developers can make this easy by breaking their changes into small
1930 self-contained commits. That won’t help in the case above, however,
1931 because the problem isn’t obvious from examination of any single
1932 commit; instead, a global view of the development is required. To
1933 make matters worse, the change in semantics in the problematic
1934 function may be just one small part of the changes in the upper
1935 line of development.</p>
1936 <p>On the other hand, if instead of merging at C you had rebased the
1937 history between Z to B on top of A, you would have gotten this
1938 linear history:</p>
1940 <p>Bisecting between Z and D* would hit a single culprit commit Y*,
1941 and understanding why Y* was broken would probably be easier.</p>
1942 <p>Partly for this reason, many experienced Git users, even when
1943 working on an otherwise merge-heavy project, keep the history
1944 linear by rebasing against the latest upstream version before
1945 publishing.</p>
1946 </div>
1947 </div>
1948 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="advanced-branch-management"></a>Chapter 6. Advanced branch management</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><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>
1950 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-individual-branches"></a>Fetching individual branches</h2></div></div></div>
1952 <p>Instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>, you can also choose just
1953 to update one branch at a time, and to store it locally under an
1954 arbitrary name:</p>
1957 repository you originally cloned from. The second argument tells Git
1962 <p>will create a new branch named <code class="literal">example-master</code> and store in it the
1964 already have a branch named example-master, it will attempt to
1965 <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a> to the commit given by example.com’s
1966 master branch. In more detail:</p>
1967 </div>
1968 <div class="section"><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>
1970 <p>In the previous example, when updating an existing branch, <code class="literal">git</code> <code class="literal">fetch</code>
1971 checks to make sure that the most recent commit on the remote
1972 branch is a descendant of the most recent commit on your copy of the
1973 branch before updating your copy of the branch to point at the new
1974 commit. Git calls this process a <a class="link" href="#fast-forwards" title="Fast-forward merges">fast-forward</a>.</p>
1977 \
1979 <p>In some cases it is possible that the new head will <span class="strong"><strong>not</strong></span> actually be
1980 a descendant of the old head. For example, the developer may have
1981 realized a serious mistake was made and decided to backtrack,
1982 resulting in a situation like:</p>
1984 \
1986 <p>In this case, <code class="literal">git</code> <code class="literal">fetch</code> will fail, and print out a warning.</p>
1987 <p>In that case, you can still force Git to update to the new head, as
1988 described in the following section. However, note that in the
1989 situation above this may mean losing the commits labeled <code class="literal">a</code> and <code class="literal">b</code>,
1990 unless you’ve already created a reference of your own pointing to
1991 them.</p>
1992 </div>
1993 <div class="section"><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>
1995 <p>If git fetch fails because the new head of a branch is not a
1996 descendant of the old head, you may force the update with:</p>
1997 <pre class="screen">$ git fetch git://example.com/proj.git +master:refs/remotes/example/master</pre>
1998 <p>Note the addition of the <code class="literal">+</code> sign. Alternatively, you can use the <code class="literal">-f</code>
1999 flag to force updates of all the fetched branches, as in:</p>
2001 <p>Be aware that commits that the old version of example/master pointed at
2002 may be lost, as we saw in the previous section.</p>
2003 </div>
2004 <div class="section"><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>
2007 repository that you originally cloned from. This information is
2008 stored in Git configuration variables, which you can see using
2011 core.repositoryformatversion=0
2012 core.filemode=true
2013 core.logallrefupdates=true
2014 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2015 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2016 branch.master.remote=origin
2017 branch.master.merge=refs/heads/master</pre>
2018 <p>If there are other repositories that you also use frequently, you can
2019 create similar configuration options to save typing; for example,</p>
2023 url = git://example.com/proj.git
2024 fetch = +refs/heads/*:refs/remotes/example/*</pre>
2025 <p>Also note that the above configuration can be performed by directly
2026 editing the file .<code class="literal">git/config</code> instead of using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>.</p>
2027 <p>After configuring the remote, the following three commands will do the
2028 same thing:</p>
2029 <pre class="screen">$ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/*
2030 $ git fetch example +refs/heads/*:refs/remotes/example/*
2031 $ git fetch example</pre>
2032 <p>See <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for more details on the configuration
2033 options mentioned above and <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> for more details on
2034 the refspec syntax.</p>
2035 </div>
2036 </div>
2037 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="git-concepts"></a>Chapter 7. Git concepts</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><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>
2039 <p>Git is built on a small number of simple but powerful ideas. While it
2040 is possible to get things done without understanding them, you will find
2041 Git much more intuitive if you do.</p>
2044 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-object-database"></a>The Object Database</h2></div></div></div>
2046 <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
2048 represent the history of a project is stored in objects with such names.
2049 In each case the name is calculated by taking the SHA-1 hash of the
2050 contents of the object. The SHA-1 hash is a cryptographic hash function.
2051 What that means to us is that it is impossible to find two different
2052 objects with the same name. This has a number of advantages; among
2053 others:</p>
2054 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
2055 Git can quickly determine whether two objects are identical or not,
2056 just by comparing names.
2058 Since object names are computed the same way in every repository, the
2059 same content stored in two repositories will always be stored under
2060 the same name.
2062 Git can detect errors when it reads an object, by checking that the
2063 object’s name is still the SHA-1 hash of its contents.
2064 </li></ul></div>
2065 <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
2069 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
2073 "blob" objects into a directory structure. In addition, a tree object
2074 can refer to other tree objects, thus creating a directory hierarchy.
2076 A <a class="link" href="#def_commit_object">"commit" object</a> ties such directory hierarchies
2078 commit contains the object name of exactly one tree designating the
2079 directory hierarchy at the time of the commit. In addition, a commit
2080 refers to "parent" commit objects that describe the history of how we
2081 arrived at that directory hierarchy.
2084 used to sign other objects. It contains the object name and type of
2085 another object, a symbolic name (of course!) and, optionally, a
2086 signature.
2087 </li></ul></div>
2089 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="commit-object"></a>Commit Object</h3></div></div></div>
2093 <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
2094 commit:</p>
2096 commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2097 tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2098 parent 257a84d9d02e90447b149af58b271c19405edb6a
2102 Fix misspelling of 'suppress' in docs
2106 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
2107 a tree: The SHA-1 name of a tree object (as defined below), representing
2108 the contents of a directory at a certain point in time.
2110 parent(s): The SHA-1 name(s) of some number of commits which represent the
2111 immediately previous step(s) in the history of the project. The
2112 example above has one parent; merge commits may have more than
2113 one. A commit with no parents is called a "root" commit, and
2114 represents the initial revision of a project. Each project must have
2115 at least one root. A project can also have multiple roots, though
2116 that isn’t common (or necessarily a good idea).
2118 an author: The name of the person responsible for this change, together
2119 with its date.
2121 a committer: The name of the person who actually created the commit,
2122 with the date it was done. This may be different from the author, for
2123 example, if the author was someone who wrote a patch and emailed it
2124 to the person who used it to create the commit.
2126 a comment describing this commit.
2127 </li></ul></div>
2128 <p>Note that a commit does not itself contain any information about what
2129 actually changed; all changes are calculated by comparing the contents
2130 of the tree referred to by this commit with the trees associated with
2131 its parents. In particular, Git does not attempt to record file renames
2132 explicitly, though it can identify cases where the existence of the same
2133 file data at changing paths suggests a rename. (See, for example, the
2134 <code class="literal">-M</code> option to <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>).</p>
2135 <p>A commit is usually created by <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a>, which creates a
2136 commit whose parent is normally the current HEAD, and whose tree is
2137 taken from the content currently stored in the index.</p>
2138 </div>
2139 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tree-object"></a>Tree Object</h3></div></div></div>
2141 <p>The ever-versatile <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command can also be used to
2142 examine tree objects, but <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a> will give you more
2143 details:</p>
2153 ...</pre>
2154 <p>As you can see, a tree object contains a list of entries, each with a
2155 mode, object type, SHA-1 name, and name, sorted by name. It represents
2156 the contents of a single directory tree.</p>
2157 <p>The object type may be a blob, representing the contents of a file, or
2158 another tree, representing the contents of a subdirectory. Since trees
2159 and blobs, like all other objects, are named by the SHA-1 hash of their
2160 contents, two trees have the same SHA-1 name if and only if their
2161 contents (including, recursively, the contents of all subdirectories)
2162 are identical. This allows Git to quickly determine the differences
2163 between two related tree objects, since it can ignore any entries with
2164 identical object names.</p>
2165 <p>(Note: in the presence of submodules, trees may also have commits as
2166 entries. See <a class="xref" href="#submodules" title="Chapter 8. Submodules">Chapter 8, <i>Submodules</i></a> for documentation.)</p>
2168 attention to the executable bit.</p>
2169 </div>
2170 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="blob-object"></a>Blob Object</h3></div></div></div>
2172 <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,
2173 for example, the blob in the entry for <code class="literal">COPYING</code> from the tree above:</p>
2176 Note that the only valid version of the GPL as far as this project
2177 is concerned is _this_ particular version of the license (ie v2, not
2178 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
2179 ...</pre>
2181 to anything else or have attributes of any kind.</p>
2182 <p>Since the blob is entirely defined by its data, if two files in a
2183 directory tree (or in multiple different versions of the repository)
2184 have the same contents, they will share the same blob object. The object
2185 is totally independent of its location in the directory tree, and
2186 renaming a file does not change the object that file is associated with.</p>
2187 <p>Note that any tree or blob object can be examined using
2188 <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> with the <revision>:<path> syntax. This can
2189 sometimes be useful for browsing the contents of a tree that is not
2190 currently checked out.</p>
2191 </div>
2192 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="trust"></a>Trust</h3></div></div></div>
2195 from another (possibly untrusted) source, you can still trust that those
2196 contents are correct as long as the SHA-1 name agrees. This is because
2197 the SHA-1 is designed so that it is infeasible to find different contents
2198 that produce the same hash.</p>
2200 to trust the contents of the entire directory that it refers to, and if
2201 you receive the SHA-1 name of a commit from a trusted source, then you
2202 can easily verify the entire history of commits reachable through
2203 parents of that commit, and all of those contents of the trees referred
2204 to by those commits.</p>
2205 <p>So to introduce some real trust in the system, the only thing you need
2206 to do is to digitally sign just <span class="emphasis"><em>one</em></span> special note, which includes the
2207 name of a top-level commit. Your digital signature shows others
2208 that you trust that commit, and the immutability of the history of
2209 commits tells others that they can trust the whole history.</p>
2210 <p>In other words, you can easily validate a whole archive by just
2211 sending out a single email that tells the people the name (SHA-1 hash)
2212 of the top commit, and digitally sign that email using something
2213 like GPG/PGP.</p>
2215 </div>
2216 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tag-object"></a>Tag Object</h3></div></div></div>
2218 <p>A tag object contains an object, object type, tag name, the name of the
2219 person ("tagger") who created the tag, and a message, which may contain
2220 a signature, as can be seen using <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a>:</p>
2222 object 437b1b20df4b356c9342dac8d38849f24ef44f27
2223 type commit
2224 tag v1.5.0
2227 GIT 1.5.0
2228 -----BEGIN PGP SIGNATURE-----
2229 Version: GnuPG v1.4.6 (GNU/Linux)
2231 iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
2232 nLE/L9aUXdWeTFPron96DLA=
2233 =2E+0
2234 -----END PGP SIGNATURE-----</pre>
2235 <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
2236 objects. (Note that <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> can also be used to create
2237 "lightweight tags", which are not tag objects at all, but just simple
2239 </div>
2240 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="pack-files"></a>How Git stores objects efficiently: pack files</h3></div></div></div>
2242 <p>Newly created objects are initially created in a file named after the
2244 <p>Unfortunately this system becomes inefficient once a project has a
2245 lot of objects. Try this on an old project:</p>
2248 <p>The first number is the number of objects which are kept in
2249 individual files. The second is the amount of space taken up by
2251 <p>You can save space and make Git faster by moving these loose objects in
2252 to a "pack file", which stores a group of objects in an efficient
2253 compressed format; the details of how pack files are formatted can be
2257 Counting objects: 6020, done.
2258 Delta compression using up to 4 threads.
2263 containing all currently unpacked objects. You can then run</p>
2266 pack. This will also remove any unreferenced objects (which may be
2267 created when, for example, you use <code class="literal">git</code> <code class="literal">reset</code> to remove a commit).
2268 You can verify that the loose objects are gone by looking at the
2272 <p>Although the object files are gone, any commands that refer to those
2273 objects will work exactly as they did before.</p>
2274 <p>The <a class="ulink" href="git-gc.html" target="_top">git-gc(1)</a> command performs packing, pruning, and more for
2275 you, so is normally the only high-level command you need.</p>
2276 </div>
2277 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="dangling-objects"></a>Dangling objects</h3></div></div></div>
2279 <p>The <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a> command will sometimes complain about dangling
2280 objects. They are not a problem.</p>
2281 <p>The most common cause of dangling objects is that you’ve rebased a
2282 branch, or you have pulled from somebody else who rebased a branch—see
2283 <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
2284 branch still exists, as does everything it pointed to. The branch
2285 pointer itself just doesn’t, since you replaced it with another one.</p>
2286 <p>There are also other situations that cause dangling objects. For
2287 example, a "dangling blob" may arise because you did a <code class="literal">git</code> <code class="literal">add</code> of a
2288 file, but then, before you actually committed it and made it part of the
2289 bigger picture, you changed something else in that file and committed
2290 that <span class="strong"><strong>updated</strong></span> thing—the old state that you added originally ends up
2291 not being pointed to by any commit or tree, so it’s now a dangling blob
2292 object.</p>
2294 there are criss-cross merges and thus more than one merge base (which is
2295 fairly unusual, but it does happen), it will generate one temporary
2296 midway tree (or possibly even more, if you had lots of criss-crossing
2297 merges and more than two merge bases) as a temporary internal merge
2298 base, and again, those are real objects, but the end result will not end
2300 <p>Generally, dangling objects aren’t anything to worry about. They can
2301 even be very useful: if you screw something up, the dangling objects can
2302 be how you recover your old tree (say, you did a rebase, and realized
2303 that you really didn’t want to—you can look at what dangling objects
2304 you have, and decide to reset your head to some old dangling state).</p>
2307 <p>This asks for all the history reachable from the given commit but not
2308 from any branch, tag, or other reference. If you decide it’s something
2309 you want, you can always create a new reference to it, e.g.,</p>
2311 <p>For blobs and trees, you can’t do the same, but you can still examine
2312 them. You can just do</p>
2314 <p>to show what the contents of the blob were (or, for a tree, basically
2315 what the <code class="literal">ls</code> for that directory was), and that may give you some idea
2316 of what the operation was that left that dangling object.</p>
2317 <p>Usually, dangling blobs and trees aren’t very interesting. They’re
2318 almost always the result of either being a half-way mergebase (the blob
2319 will often even have the conflict markers from a merge in it, if you
2320 have had conflicting merges that you fixed up by hand), or simply
2321 because you interrupted a <code class="literal">git</code> <code class="literal">fetch</code> with ^C or something like that,
2322 leaving <span class="emphasis"><em>some</em></span> of the new objects in the object database, but just
2323 dangling and useless.</p>
2324 <p>Anyway, once you are sure that you’re not interested in any dangling
2325 state, you can just prune all unreachable objects:</p>
2327 <p>and they’ll be gone. (You should only run <code class="literal">git</code> <code class="literal">prune</code> on a quiescent
2328 repository—it’s kind of like doing a filesystem fsck recovery: you
2329 don’t want to do that while the filesystem is mounted.
2330 <code class="literal">git</code> <code class="literal">prune</code> is designed not to cause any harm in such cases of concurrent
2331 accesses to a repository but you might receive confusing or scary messages.)</p>
2332 </div>
2333 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="recovering-from-repository-corruption"></a>Recovering from repository corruption</h3></div></div></div>
2335 <p>By design, Git treats data trusted to it with caution. However, even in
2336 the absence of bugs in Git itself, it is still possible that hardware or
2337 operating system errors could corrupt data.</p>
2338 <p>The first defense against such problems is backups. You can back up a
2339 Git directory using clone, or just using cp, tar, or any other backup
2340 mechanism.</p>
2341 <p>As a last resort, you can search for the corrupted objects and attempt
2342 to replace them by hand. Back up your repository before attempting this
2343 in case you corrupt things even more in the process.</p>
2344 <p>We’ll assume that the problem is a single missing or corrupted blob,
2345 which is sometimes a solvable problem. (Recovering missing trees and
2347 <p>Before starting, verify that there is corruption, and figure out where
2348 it is with <a class="ulink" href="git-fsck.html" target="_top">git-fsck(1)</a>; this may be time-consuming.</p>
2351 broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
2352 to blob 4b9458b3786228369c63936db65827de3cc06200
2355 points to it. If you could find just one copy of that missing blob
2356 object, possibly in some other repository, you could move it into
2358 still examine the tree that pointed to it with <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>,
2359 which might output something like:</p>
2362 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap
2363 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING
2364 ...
2366 ...</pre>
2367 <p>So now you know that the missing blob was the data for a file named
2368 <code class="literal">myfile</code>. And chances are you can also identify the directory—let’s
2369 say it’s in <code class="literal">somedirectory</code>. If you’re lucky the missing copy might be
2370 the same as the copy you have checked out in your working tree at
2374 <p>which will create and store a blob object with the contents of
2375 somedirectory/myfile, and output the SHA-1 of that object. if you’re
2376 extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
2377 which case you’ve guessed right, and the corruption is fixed!</p>
2378 <p>Otherwise, you need more information. How do you tell which version of
2379 the file has been lost?</p>
2384 Author:
2385 Date:
2386 ...
2387 :100644 100644 4b9458b newsha M somedirectory/myfile
2390 commit xyz
2391 Author:
2392 Date:
2394 ...
2396 <p>This tells you that the immediately following version of the file was
2398 You also know the commit messages that went with the change from oldsha
2400 <p>If you’ve been committing small enough changes, you may now have a good
2405 <p>(Btw, you could have ignored the <code class="literal">fsck</code>, and started with doing a</p>
2408 whole thing. It’s up to you—Git does <span class="strong"><strong>have</strong></span> a lot of information, it is
2409 just missing one particular blob version.</p>
2410 </div>
2411 </div>
2412 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-index"></a>The index</h2></div></div></div>
2414 <p>The index is a binary file (generally kept in .<code class="literal">git/index</code>) containing a
2415 sorted list of path names, each with permissions and the SHA-1 of a blob
2416 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>
2423 ...
2427 <p>Note that in older documentation you may see the index called the
2429 properties:</p>
2432 (uniquely determined) tree object.</p>
2433 <p class="simpara">For example, running <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> generates this tree object
2434 from the index, stores it in the object database, and uses it as the
2435 tree object associated with the new commit.</p>
2438 and the working tree.</p>
2440 the last modified time). This data is not displayed above, and is not
2441 stored in the created tree object, but it can be used to determine
2442 quickly which files in the working directory differ from what was
2443 stored in the index, and thus save Git from having to read all of the
2444 data from such files to look for changes.</p>
2447 between different tree objects, allowing each pathname to be
2448 associated with sufficient information about the trees involved that
2449 you can create a three-way merge between them.</p>
2450 <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
2451 store multiple versions of a single file (called "stages"). The third
2452 column in the <a class="ulink" href="git-ls-files.html" target="_top">git-ls-files(1)</a> output above is the stage
2453 number, and will take on values other than 0 for files with merge
2454 conflicts.</p>
2455 </li></ol></div>
2456 <p>The index is thus a sort of temporary staging area, which is filled with
2457 a tree which you are in the process of working on.</p>
2458 <p>If you blow the index away entirely, you generally haven’t lost any
2459 information as long as you have the name of the tree that it described.</p>
2460 </div>
2461 </div>
2462 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="submodules"></a>Chapter 8. Submodules</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#pitfalls-with-submodules">Pitfalls with submodules</a></span></dt></dl></div>
2464 <p>Large projects are often composed of smaller, self-contained modules. For
2465 example, an embedded Linux distribution’s source tree would include every
2466 piece of software in the distribution with some local modifications; a movie
2467 player might need to build against a specific, known-working version of a
2468 decompression library; several independent programs might all share the same
2469 build scripts.</p>
2470 <p>With centralized revision control systems this is often accomplished by
2471 including every module in one single repository. Developers can check out
2472 all modules or only the modules they need to work with. They can even modify
2473 files across several modules in a single commit while moving things around
2474 or updating APIs and translations.</p>
2475 <p>Git does not allow partial checkouts, so duplicating this approach in Git
2476 would force developers to keep a local copy of modules they are not
2477 interested in touching. Commits in an enormous checkout would be slower
2478 than you’d expect as Git would have to scan every directory for changes.
2479 If modules have a lot of local history, clones would take forever.</p>
2480 <p>On the plus side, distributed revision control systems can much better
2481 integrate with external sources. In a centralized model, a single arbitrary
2482 snapshot of the external project is exported from its own revision control
2483 and then imported into the local revision control on a vendor branch. All
2484 the history is hidden. With distributed revision control you can clone the
2485 entire external history and much more easily follow development and re-merge
2486 local changes.</p>
2487 <p>Git’s submodule support allows a repository to contain, as a subdirectory, a
2488 checkout of an external project. Submodules maintain their own identity;
2489 the submodule support just stores the submodule repository location and
2490 commit ID, so other developers who clone the containing project
2491 ("superproject") can easily clone all the submodules at the same revision.
2492 Partial checkouts of the superproject are possible: you can tell Git to
2493 clone none, some or all of the submodules.</p>
2494 <p>The <a class="ulink" href="git-submodule.html" target="_top">git-submodule(1)</a> command is available since Git 1.5.3. Users
2495 with Git 1.5.2 can look up the submodule commits in the repository and
2496 manually check them out; earlier versions won’t recognize the submodules at
2497 all.</p>
2498 <p>To see how submodule support works, create four example
2499 repositories that can be used later as a submodule:</p>
2501 $ cd ~/git
2502 $ for i in a b c d
2503 do
2504 mkdir $i
2505 cd $i
2506 git init
2508 git add $i.txt
2509 git commit -m "Initial commit, submodule $i"
2510 cd ..
2511 done</pre>
2514 $ cd super
2515 $ git init
2516 $ for i in a b c d
2517 do
2518 git submodule add ~/git/$i $i
2519 done</pre>
2522 </div>
2523 <p>See what files <code class="literal">git</code> <code class="literal">submodule</code> created:</p>
2525 . .. .git .gitmodules a b c d</pre>
2526 <p>The <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">add</code> <span class="emphasis"><em><repo></em></span> <span class="emphasis"><em><path></em></span> command does a couple of things:</p>
2527 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
2528 It clones the submodule from <span class="emphasis"><em><repo></em></span> to the given <span class="emphasis"><em><path></em></span> under the
2529 current directory and by default checks out the master branch.
2531 It adds the submodule’s clone path to the <a class="ulink" href="gitmodules.html" target="_top">gitmodules(5)</a> file and
2532 adds this file to the index, ready to be committed.
2534 It adds the submodule’s current commit ID to the index, ready to be
2535 committed.
2536 </li></ul></div>
2541 $ git clone super cloned
2542 $ cd cloned</pre>
2545 . ..
2546 $ git submodule status
2547 -d266b9873ad50488163457f025db7cdd9683d88b a
2548 -e81d457da15309b4fef4249aba9b50187999670d b
2549 -c1536a972b9affea0f16e0680ba87332dc059146 c
2550 -d96249ff5d57de5de093e6baff9e0aafa5276a74 d</pre>
2552 <p>The commit object names shown above would be different for you, but they
2553 should match the HEAD commit object names of your repositories. You can check
2554 it by running <code class="literal">git</code> <code class="literal">ls-remote</code> <code class="literal">..</code><code class="literal">/a</code>.</p>
2555 </div>
2556 <p>Pulling down the submodules is a two-step process. First run <code class="literal">git</code> <code class="literal">submodule</code>
2557 <code class="literal">init</code> to add the submodule repository URLs to .<code class="literal">git/config</code>:</p>
2559 <p>Now use <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">update</code> to clone the repositories and check out the
2560 commits specified in the superproject:</p>
2562 $ cd a
2563 $ ls -a
2564 . .. .git a.txt</pre>
2565 <p>One major difference between <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">update</code> and <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">add</code> is
2566 that <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">update</code> checks out a specific commit, rather than the tip
2567 of a branch. It’s like checking out a tag: the head is detached, so you’re not
2568 working on a branch.</p>
2570 * (detached from d266b98)
2571 master</pre>
2572 <p>If you want to make a change within a submodule and you have a detached head,
2573 then you should create or checkout a branch, make your changes, publish the
2574 change within the submodule, and then update the superproject to reference the
2575 new commit:</p>
2581 $ git commit -a -m "Updated the submodule from within the superproject."
2582 $ git push
2583 $ cd ..
2584 $ git diff
2585 diff --git a/a b/a
2587 --- a/a
2588 +++ b/a
2590 -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
2591 +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
2592 $ git add a
2593 $ git commit -m "Updated submodule a."
2594 $ git push</pre>
2595 <p>You have to run <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">update</code> after <code class="literal">git</code> <code class="literal">pull</code> if you want to update
2596 submodules, too.</p>
2597 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="pitfalls-with-submodules"></a>Pitfalls with submodules</h2></div></div></div>
2599 <p>Always publish the submodule change before publishing the change to the
2600 superproject that references it. If you forget to publish the submodule change,
2601 others won’t be able to clone the repository:</p>
2603 $ echo i added another line to this file >> a.txt
2604 $ git commit -a -m "doing it wrong this time"
2605 $ cd ..
2606 $ git add a
2607 $ git commit -m "Updated submodule a again."
2608 $ git push
2609 $ cd ~/git/cloned
2610 $ git pull
2611 $ git submodule update
2612 error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
2613 Did you forget to 'git add'?
2615 <p>In older Git versions it could be easily forgotten to commit new or modified
2616 files in a submodule, which silently leads to similar problems as not pushing
2617 the submodule changes. Starting with Git 1.7.0 both <code class="literal">git</code> <code class="literal">status</code> and <code class="literal">git</code> <code class="literal">diff</code>
2618 in the superproject show submodules as modified when they contain new or
2619 modified files to protect against accidentally committing such a state. <code class="literal">git</code>
2620 <code class="literal">diff</code> will also add a <code class="literal">-dirty</code> to the work tree side when generating patch
2623 diff --git a/sub b/sub
2624 --- a/sub
2625 +++ b/sub
2627 -Subproject commit 3f356705649b5d566d97ff843cf193359229a453
2628 +Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty
2629 $ git diff --submodule
2631 <p>You also should not rewind branches in a submodule beyond commits that were
2632 ever recorded in any superproject.</p>
2633 <p>It’s not safe to run <code class="literal">git</code> <code class="literal">submodule</code> <code class="literal">update</code> if you’ve made and committed
2634 changes within a submodule without checking out a branch first. They will be
2635 silently overwritten:</p>
2637 module a
2638 $ echo line added from private2 >> a.txt
2639 $ git commit -a -m "line added inside private2"
2640 $ cd ..
2641 $ git submodule update
2642 Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
2643 $ cd a
2644 $ cat a.txt
2645 module a</pre>
2648 </div>
2649 <p>If you have uncommitted changes in your submodule working tree, <code class="literal">git</code>
2650 <code class="literal">submodule</code> <code class="literal">update</code> will not overwrite them. Instead, you get the usual
2651 warning about not being able switch from a dirty branch.</p>
2652 </div>
2653 </div>
2654 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="low-level-operations"></a>Chapter 9. Low-level Git operations</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><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>
2656 <p>Many of the higher-level commands were originally implemented as shell
2657 scripts using a smaller core of low-level Git commands. These can still
2658 be useful when doing unusual things with Git, or just as a way to
2659 understand its inner workings.</p>
2660 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-manipulation"></a>Object access and manipulation</h2></div></div></div>
2662 <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,
2663 though the higher-level <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> is usually more useful.</p>
2664 <p>The <a class="ulink" href="git-commit-tree.html" target="_top">git-commit-tree(1)</a> command allows constructing commits with
2665 arbitrary parents and trees.</p>
2666 <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
2667 accessed by <a class="ulink" href="git-ls-tree.html" target="_top">git-ls-tree(1)</a>. Two trees can be compared with
2669 <p>A tag is created with <a class="ulink" href="git-mktag.html" target="_top">git-mktag(1)</a>, and the signature can be
2670 verified by <a class="ulink" href="git-verify-tag.html" target="_top">git-verify-tag(1)</a>, though it is normally simpler to
2672 </div>
2673 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="the-workflow"></a>The Workflow</h2></div></div></div>
2675 <p>High-level operations such as <a class="ulink" href="git-commit.html" target="_top">git-commit(1)</a> and
2677 between the working tree, the index, and the object database. Git
2678 provides low-level operations which perform each of these steps
2679 individually.</p>
2680 <p>Generally, all Git operations work on the index file. Some operations
2681 work <span class="strong"><strong>purely</strong></span> on the index file (showing the current state of the
2682 index), but most operations move data between the index file and either
2683 the database or the working directory. Thus there are four main
2684 combinations:</p>
2685 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="working-directory-to-index"></a>working directory → index</h3></div></div></div>
2687 <p>The <a class="ulink" href="git-update-index.html" target="_top">git-update-index(1)</a> command updates the index with
2688 information from the working directory. You generally update the
2689 index information by just specifying the filename you want to update,
2690 like so:</p>
2692 <p>but to avoid common mistakes with filename globbing etc., the command
2693 will not normally add totally new entries or remove old entries,
2694 i.e. it will normally just update existing cache entries.</p>
2695 <p>To tell Git that yes, you really do realize that certain files no
2696 longer exist, or that new files should be added, you
2697 should use the <code class="literal">--remove</code> and <code class="literal">--add</code> flags respectively.</p>
2698 <p>NOTE! A <code class="literal">--remove</code> flag does <span class="emphasis"><em>not</em></span> mean that subsequent filenames will
2699 necessarily be removed: if the files still exist in your directory
2700 structure, the index will be updated with their new status, not
2701 removed. The only thing <code class="literal">--remove</code> means is that update-index will be
2702 considering a removed file to be a valid thing, and if the file really
2703 does not exist any more, it will update the index accordingly.</p>
2704 <p>As a special case, you can also do <code class="literal">git</code> <code class="literal">update-index</code> <code class="literal">--refresh</code>, which
2705 will refresh the "stat" information of each index to match the current
2706 stat information. It will <span class="emphasis"><em>not</em></span> update the object status itself, and
2707 it will only update the fields that are used to quickly test whether
2708 an object still matches its old backing store object.</p>
2709 <p>The previously introduced <a class="ulink" href="git-add.html" target="_top">git-add(1)</a> is just a wrapper for
2711 </div>
2712 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-object-database"></a>index → object database</h3></div></div></div>
2716 <p>that doesn’t come with any options—it will just write out the
2717 current index into the set of tree objects that describe that state,
2718 and it will return the name of the resulting top-level tree. You can
2719 use that tree to re-generate the index at any time by going in the
2720 other direction:</p>
2721 </div>
2722 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="object-database-to-index"></a>object database → index</h3></div></div></div>
2725 populate (and overwrite—don’t do this if your index contains any
2726 unsaved state that you might want to restore later!) your current
2727 index. Normal operation is just</p>
2729 <p>and your index file will now be equivalent to the tree that you saved
2730 earlier. However, that is only your <span class="emphasis"><em>index</em></span> file: your working
2731 directory contents have not been modified.</p>
2732 </div>
2733 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="index-to-working-directory"></a>index → working directory</h3></div></div></div>
2736 files. This is not a very common operation, since normally you’d just
2737 keep your files updated, and rather than write to your working
2738 directory, you’d tell the index files about the changes in your
2739 working directory (i.e. <code class="literal">git</code> <code class="literal">update-index</code>).</p>
2740 <p>However, if you decide to jump to a new version, or check out somebody
2741 else’s version, or just restore a previous tree, you’d populate your
2742 index file with read-tree, and then you need to check out the result
2743 with</p>
2746 <p>NOTE! <code class="literal">git</code> <code class="literal">checkout-index</code> normally refuses to overwrite old files, so
2747 if you have an old version of the tree already checked out, you will
2748 need to use the <code class="literal">-f</code> flag (<span class="emphasis"><em>before</em></span> the <code class="literal">-a</code> flag or the filename) to
2750 <p>Finally, there are a few odds and ends which are not purely moving
2751 from one representation to the other:</p>
2752 </div>
2753 <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="tying-it-all-together"></a>Tying it all together</h3></div></div></div>
2755 <p>To commit a tree you have instantiated with <code class="literal">git</code> <code class="literal">write-tree</code>, you’d
2756 create a "commit" object that refers to that tree and the history
2757 behind it—most notably the "parent" commits that preceded it in
2758 history.</p>
2760 before a certain change was made. However, sometimes it can have two
2761 or more parent commits, in which case we call it a "merge", due to the
2762 fact that such a commit brings together ("merges") two or more
2763 previous states represented by other commits.</p>
2765 of a working directory, a "commit" represents that state in time,
2766 and explains how we got there.</p>
2767 <p>You create a commit object by giving it the tree that describes the
2768 state at the time of the commit, and a list of parents:</p>
2769 <pre class="screen">$ git commit-tree <tree> -p <parent> [(-p <parent2>)...]</pre>
2770 <p>and then giving the reason for the commit on stdin (either through
2771 redirection from a pipe or file, or by just typing it at the tty).</p>
2772 <p><code class="literal">git</code> <code class="literal">commit-tree</code> will return the name of the object that represents
2773 that commit, and you should save it away for later use. Normally,
2774 you’d commit a new <code class="literal">HEAD</code> state, and while Git doesn’t care where you
2775 save the note about that state, in practice we tend to just write the
2776 result to the file pointed at by .<code class="literal">git/HEAD</code>, so that we can always see
2777 what the last committed state was.</p>
2780 commit obj
2781 +----+
2782 | |
2783 | |
2784 V V
2785 +-----------+
2786 | Object DB |
2787 | Backing |
2788 | Store |
2789 +-----------+
2790 ^
2791 write-tree | |
2792 tree obj | |
2793 | | read-tree
2794 | | tree obj
2795 V
2796 +-----------+
2797 | Index |
2798 | "cache" |
2799 +-----------+
2800 update-index ^
2801 blob obj | |
2802 | |
2803 checkout-index -u | | checkout-index
2804 stat | | blob obj
2805 V
2806 +-----------+
2807 | Working |
2808 | Directory |
2809 +-----------+</pre>
2810 </div>
2811 </div>
2812 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-the-data"></a>Examining the data</h2></div></div></div>
2814 <p>You can examine the data represented in the object database and the
2815 index with various helper tools. For every object, you can use
2816 <a class="ulink" href="git-cat-file.html" target="_top">git-cat-file(1)</a> to examine details about the
2817 object:</p>
2819 <p>shows the type of the object, and once you have the type (which is
2820 usually implicit in where you find the object), you can use</p>
2822 <p>to show its contents. NOTE! Trees have binary content, and as a result
2823 there is a special helper for showing that content, called
2824 <code class="literal">git</code> <code class="literal">ls-tree</code>, which turns the binary content into a more easily
2825 readable form.</p>
2827 tend to be small and fairly self-explanatory. In particular, if you
2829 you can do</p>
2832 </div>
2833 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging-multiple-trees"></a>Merging multiple trees</h2></div></div></div>
2835 <p>Git can help you perform a three-way merge, which can in turn be
2836 used for a many-way merge by repeating the merge procedure several
2837 times. The usual situation is that you only do one three-way merge
2838 (reconciling two lines of history) and commit the result, but if
2839 you like to, you can merge several branches in one go.</p>
2840 <p>To perform a three-way merge, you start with the two commits you
2841 want to merge, find their closest common parent (a third commit),
2842 and compare the trees corresponding to these three commits.</p>
2844 commits:</p>
2846 <p>This prints the name of a commit they are both based on. You should
2847 now look up the tree objects of those commits, which you can easily
2848 do with</p>
2850 <p>since the tree object information is always the first line in a commit
2851 object.</p>
2853 tree, aka the common tree, and the two "result" trees, aka the branches
2854 you want to merge), you do a "merge" read into the index. This will
2855 complain if it has to throw away your old index contents, so you should
2856 make sure that you’ve committed those—in fact you would normally
2857 always do a merge against your last commit (which should thus match what
2858 you have in your current index anyway).</p>
2860 <pre class="screen">$ git read-tree -m -u <origtree> <yourtree> <targettree></pre>
2861 <p>which will do all trivial merge operations for you directly in the
2862 index file, and you can just write the result out with
2864 </div>
2865 <div class="section"><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>
2867 <p>Sadly, many merges aren’t trivial. If there are files that have
2868 been added, moved or removed, or if both branches have modified the
2869 same file, you will be left with an index tree that contains "merge
2870 entries" in it. Such an index tree can <span class="emphasis"><em>NOT</em></span> be written out to a tree
2871 object, and you will have to resolve any such merge clashes using
2872 other tools before you can write out the result.</p>
2873 <p>You can examine such index state with <code class="literal">git</code> <code class="literal">ls-files</code> <code class="literal">--unmerged</code>
2874 command. An example:</p>
2876 $ git ls-files --unmerged
2880 <p>Each line of the <code class="literal">git</code> <code class="literal">ls-files</code> <code class="literal">--unmerged</code> output begins with
2882 filename. The <span class="emphasis"><em>stage number</em></span> is Git’s way to say which tree it
2884 the <code class="literal">HEAD</code> tree, and stage 3 to the <code class="literal">$target</code> tree.</p>
2885 <p>Earlier we said that trivial merges are done inside
2886 <code class="literal">git</code> <code class="literal">read-tree</code> <code class="literal">-m</code>. For example, if the file did not change
2887 from <code class="literal">$orig</code> to <code class="literal">HEAD</code> or <code class="literal">$target</code>, or if the file changed
2888 from <code class="literal">$orig</code> to <code class="literal">HEAD</code> and <code class="literal">$orig</code> to <code class="literal">$target</code> the same way,
2891 <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.
2892 You could resolve this by running your favorite 3-way merge
2893 program, e.g. <code class="literal">diff3</code>, <code class="literal">merge</code>, or Git’s own merge-file, on
2894 the blob objects from these three stages yourself, like this:</p>
2900 with conflict markers if there are conflicts. After verifying
2901 the merge result makes sense, you can tell Git what the final
2902 merge result for this file is by:</p>
2904 $ git update-index hello.c</pre>
2905 <p>When a path is in the "unmerged" state, running <code class="literal">git</code> <code class="literal">update-index</code> for
2906 that path tells Git to mark the path resolved.</p>
2907 <p>The above is the description of a Git merge at the lowest level,
2908 to help you understand what conceptually happens under the hood.
2909 In practice, nobody, not even Git itself, runs <code class="literal">git</code> <code class="literal">cat-file</code> three times
2910 for this. There is a <code class="literal">git</code> <code class="literal">merge-index</code> program that extracts the
2913 <p>and that is what higher level <code class="literal">git</code> <code class="literal">merge</code> <code class="literal">-s</code> <code class="literal">resolve</code> is implemented with.</p>
2914 </div>
2915 </div>
2916 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="hacking-git"></a>Chapter 10. Hacking Git</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><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>
2918 <p>This chapter covers internal details of the Git implementation which
2919 probably only Git developers need to understand.</p>
2920 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="object-details"></a>Object storage format</h2></div></div></div>
2923 format of the object (i.e. how it is used, and how it can refer to other
2924 objects). There are currently four different object types: "blob",
2926 <p>Regardless of object type, all objects share the following
2927 characteristics: they are all deflated with zlib, and have a header
2928 that not only specifies their type, but also provides size information
2929 about the data in the object. It’s worth noting that the SHA-1 hash
2930 that is used to name the object is the hash of the original data
2931 plus this header, so <code class="literal">sha1sum</code> <span class="emphasis"><em>file</em></span> does not match the object name
2932 for <span class="emphasis"><em>file</em></span> (the earliest versions of Git hashed slightly differently
2933 but the conclusion is still the same).</p>
2934 <p>The following is a short example that demonstrates how these hashes
2935 can be generated manually:</p>
2939 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
2940 The object we want the hash for is of type "blob" and its size is
2941 12 bytes.
2943 Prepend the object header to the file content and feed this to
2945 </li></ul></div>
2948 <p>This manually constructed hash can be verified using <code class="literal">git</code> <code class="literal">hash-object</code>
2949 which of course hides the addition of the header:</p>
2952 <p>As a result, the general consistency of an object can always be tested
2953 independently of the contents or the type of the object: all objects can
2954 be validated by verifying that (a) their hashes match the content of the
2955 file and (b) the object successfully inflates to a stream of bytes that
2956 forms a sequence of
2957 <span class="emphasis"><em><ascii-type-without-space></em></span> <code class="literal">+</code> <span class="emphasis"><em><space></em></span> <code class="literal">+</code> <span class="emphasis"><em><ascii-decimal-size></em></span> <code class="literal">+</code>
2958 <byte\0> <code class="literal">+</code> <span class="emphasis"><em><binary-object-data></em></span>.</p>
2959 <p>The structured objects can further have their structure and
2960 connectivity to other objects verified. This is generally done with
2961 the <code class="literal">git</code> <code class="literal">fsck</code> program, which generates a full dependency graph
2962 of all objects, and verifies their internal consistency (in addition
2963 to just verifying their superficial consistency through the hash).</p>
2964 </div>
2965 <div class="section"><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>
2967 <p>It is not always easy for new developers to find their way through Git’s
2968 source code. This section gives you a little guidance to show where to
2969 start.</p>
2972 <p>The initial revision lays the foundation for almost everything Git has
2973 today (even though details may differ in a few places), but is small
2974 enough to read in one sitting.</p>
2975 <p>Note that terminology has changed since that revision. For example, the
2976 README in that revision uses the word "changeset" to describe what we
2980 <p>If you grasp the ideas in that initial commit, you should check out a
2981 more recent version and skim <code class="literal">read-cache-ll.h</code>, <code class="literal">object.h</code> and <code class="literal">commit.h</code>.</p>
2982 <p>In the early days, Git (in the tradition of UNIX) was a bunch of programs
2983 which were extremely simple, and which you used in scripts, piping the
2984 output of one into another. This turned out to be good for initial
2985 development, since it was easier to test new things. However, recently
2986 many of these parts have become builtins, and some of the core has been
2987 "libified", i.e. put into libgit.a for performance, portability reasons,
2988 and to avoid code duplication.</p>
2989 <p>By now, you know what the index is (and find the corresponding data
2990 structures in <code class="literal">read-cache-ll.h</code>), and that there are just a couple of
2991 object types (blobs, trees, commits and tags) which inherit their
2992 common structure from <code class="literal">struct</code> <code class="literal">object</code>, which is their first member
2993 (and thus, you can cast e.g. (<code class="literal">struct</code> <code class="literal">object</code> *)<code class="literal">commit</code> to achieve the
2994 <span class="emphasis"><em>same</em></span> as &commit-><code class="literal">object</code>, i.e. get at the object name and flags).</p>
2996 <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>.
2997 There are quite a few ways to name an object (and not only revisions!).
2998 All of these are handled in <code class="literal">sha1_name.c</code>. Just have a quick look at
3001 <p>This is just to get you into the groove for the most libified part of Git:
3002 the revision walker.</p>
3003 <p>Basically, the initial version of <code class="literal">git</code> <code class="literal">log</code> was a shell script:</p>
3005 LESS=-S ${PAGER:-less}</pre>
3007 <p><code class="literal">git</code> <code class="literal">rev-list</code> is the original version of the revision walker, which
3008 <span class="emphasis"><em>always</em></span> printed a list of revisions to stdout. It is still functional,
3009 and needs to, since most new Git commands start out as scripts using
3011 <p><code class="literal">git</code> <code class="literal">rev-parse</code> is not as important any more; it was only used to filter out
3012 options that were relevant for the different plumbing commands that were
3013 called by the script.</p>
3014 <p>Most of what <code class="literal">git</code> <code class="literal">rev-list</code> did is contained in <code class="literal">revision.c</code> and
3015 <code class="literal">revision.h</code>. It wraps the options in a struct named <code class="literal">rev_info</code>, which
3016 controls how and what revisions are walked, and more.</p>
3017 <p>The original job of <code class="literal">git</code> <code class="literal">rev-parse</code> is now taken by the function
3018 <code class="literal">setup_revisions</code>(), which parses the revisions and the common command-line
3019 options for the revision walker. This information is stored in the struct
3020 <code class="literal">rev_info</code> for later consumption. You can do your own command-line option
3021 parsing after calling <code class="literal">setup_revisions</code>(). After that, you have to call
3022 <code class="literal">prepare_revision_walk</code>() for initialization, and then you can get the
3024 <p>If you are interested in more details of the revision walking process,
3026 <code class="literal">git</code> <code class="literal">show</code> <code class="literal">v1.3.0~155^2~4</code> and scroll down to that function (note that you
3028 <p>Nowadays, <code class="literal">git</code> <code class="literal">log</code> is a builtin, which means that it is <span class="emphasis"><em>contained</em></span> in the
3030 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3031 a function called <code class="literal">cmd_</code><span class="emphasis"><em><bla></em></span>, typically defined in <code class="literal">builtin/</code><bla.<code class="literal">c</code>>
3032 (note that older versions of Git used to have it in <code class="literal">builtin-</code><span class="emphasis"><em><bla></em></span><code class="literal">.c</code>
3035 an entry in the <code class="literal">commands</code>[] array in <code class="literal">git.c</code>, and
3037 an entry in <code class="literal">BUILTIN_OBJECTS</code> in the <code class="literal">Makefile</code>.
3038 </li></ul></div>
3039 <p>Sometimes, more than one builtin is contained in one source file. For
3040 example, <code class="literal">cmd_whatchanged</code>() and <code class="literal">cmd_log</code>() both reside in <code class="literal">builtin/log.c</code>,
3041 since they share quite a bit of code. In that case, the commands which are
3042 <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
3044 <p><code class="literal">git</code> <code class="literal">log</code> looks more complicated in C than it does in the original script,
3045 but that allows for a much greater flexibility and performance.</p>
3047 <p>Lesson three is: study the code. Really, it is the best way to learn about
3048 the organization of Git (after you know the basic concepts).</p>
3050 access a blob just knowing the object name of it?". The first step is to
3051 find a Git command with which you can do it. In this example, it is either
3052 <code class="literal">git</code> <code class="literal">show</code> or <code class="literal">git</code> <code class="literal">cat-file</code>.</p>
3053 <p>For the sake of clarity, let’s stay with <code class="literal">git</code> <code class="literal">cat-file</code>, because it</p>
3054 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3055 is plumbing, and
3057 was around even in the initial commit (it literally went only through
3058 some 20 revisions as <code class="literal">cat-file.c</code>, was renamed to <code class="literal">builtin/cat-file.c</code>
3059 when made a builtin, and then saw less than 10 versions).
3060 </li></ul></div>
3061 <p>So, look into <code class="literal">builtin/cat-file.c</code>, search for <code class="literal">cmd_cat_file</code>() and look what
3062 it does.</p>
3064 if (argc != 3)
3065 usage("git cat-file [-t|-s|-e|-p|<type>] <sha1>");
3066 if (get_sha1(argv[2], sha1))
3068 <p>Let’s skip over the obvious details; the only really interesting part
3069 here is the call to <code class="literal">get_sha1</code>(). It tries to interpret <code class="literal">argv</code>[<code class="literal">2</code>] as an
3070 object name, and if it refers to an object which is present in the current
3071 repository, it writes the resulting SHA-1 into the variable <code class="literal">sha1</code>.</p>
3073 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3074 <code class="literal">get_sha1</code>() returns 0 on <span class="emphasis"><em>success</em></span>. This might surprise some new
3075 Git hackers, but there is a long tradition in UNIX to return different
3076 negative numbers in case of different errors—and 0 on success.
3078 the variable <code class="literal">sha1</code> in the function signature of <code class="literal">get_sha1</code>() is <code class="literal">unsigned</code>
3079 <code class="literal">char</code> *, but is actually expected to be a pointer to <code class="literal">unsigned</code>
3080 <code class="literal">char</code>[<code class="literal">20</code>]. This variable will contain the 160-bit SHA-1 of the given
3081 commit. Note that whenever a SHA-1 is passed as <code class="literal">unsigned</code> <code class="literal">char</code> *, it
3082 is the binary representation, as opposed to the ASCII representation in
3084 </li></ul></div>
3089 <p>This is how you read a blob (actually, not only a blob, but any type of
3090 object). To know how the function <code class="literal">read_object_with_reference</code>() actually
3091 works, find the source code for it (something like <code class="literal">git</code> <code class="literal">grep</code>
3092 <code class="literal">read_object_with</code> | <code class="literal">grep</code> ":[<code class="literal">a-z</code>]" in the Git repository), and read
3093 the source.</p>
3094 <p>To find out how the result can be used, just read on in <code class="literal">cmd_cat_file</code>():</p>
3096 <p>Sometimes, you do not know where to look for a feature. In many such cases,
3097 it helps to search through the output of <code class="literal">git</code> <code class="literal">log</code>, and then <code class="literal">git</code> <code class="literal">show</code> the
3098 corresponding commit.</p>
3099 <p>Example: If you know that there was some test case for <code class="literal">git</code> <code class="literal">bundle</code>, but
3100 do not remember where it was (yes, you <span class="emphasis"><em>could</em></span> <code class="literal">git</code> <code class="literal">grep</code> <code class="literal">bundle</code> <code class="literal">t/</code>, but that
3101 does not illustrate the point!):</p>
3103 <p>In the pager (<code class="literal">less</code>), just search for "bundle", go a few lines back,
3104 and see that it is in commit 18449ab0. Now just copy this object name,
3105 and paste it into the command line</p>
3108 <p>Another example: Find out what to do in order to make some script a
3109 builtin:</p>
3111 <p>You see, Git is actually the best tool to find out about the source of Git
3112 itself!</p>
3113 </div>
3114 </div>
3115 <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="glossary"></a>Chapter 11. Git Glossary</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></div>
3117 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="git-explained"></a>Git explained</h2></div></div></div>
3119 <div class="variablelist"><dl class="variablelist"><dt><span class="term"><a name="def_alternate_object_database"></a>alternate object database</span></dt><dd>
3122 from another object database, which is called an "alternate".
3124 A bare repository is normally an appropriately
3125 named <a class="link" href="#def_directory">directory</a> with a .<code class="literal">git</code> suffix that does not
3126 have a locally checked-out copy of any of the files under
3127 revision control. That is, all of the Git
3128 administrative and control files that would normally be present in the
3131 and no other files are present and checked out. Usually publishers of
3132 public repositories make bare repositories available.
3136 A "branch" is a line of development. The most recent
3138 that branch. The tip of the branch is <a class="link" href="#def_ref">referenced</a> by a branch
3140 is done on the branch. A single Git
3148 A list of objects, where each <a class="link" href="#def_object">object</a> in the list contains
3149 a reference to its successor (for example, the successor of a
3150 <a class="link" href="#def_commit">commit</a> could be one of its <a class="link" href="#def_parent">parents</a>).
3153 store changes, but states, it really does not make sense to use the term
3154 "changesets" with Git.
3156 The action of updating all or part of the
3157 <a class="link" href="#def_working_tree">working tree</a> with a <a class="link" href="#def_tree_object">tree object</a>
3160 <a class="link" href="#def_index">index</a> and <a class="link" href="#def_HEAD">HEAD</a> if the whole working tree has
3164 changes out of a series of changes (typically commits) and record them
3165 as a new series of changes on top of a different codebase. In Git, this is
3166 performed by the "git cherry-pick" command to extract the change introduced
3172 <a class="link" href="#def_head">head</a>. Also see "<a class="link" href="#def_dirty">dirty</a>".
3175 Git history; the entire history of a project is represented as a
3176 set of interrelated commits. The word "commit" is often
3177 used by Git in the same places other revision control systems
3181 state in the Git history, by creating a new commit representing the current
3182 state of the <a class="link" href="#def_index">index</a> and advancing <a class="link" href="#def_HEAD">HEAD</a>
3183 to point at the new commit.</p>
3184 </dd><dt><span class="term"><a name="def_commit_graph_general"></a>commit graph concept, representations and usage</span></dt><dd>
3188 This structure is the definitive commit graph. The
3189 graph can be represented in other ways, e.g. the
3191 </dd><dt><span class="term"><a name="def_commit_graph_file"></a>commit-graph file</span></dt><dd>
3192 The "commit-graph" (normally hyphenated) file is a supplemental
3194 which accelerates commit graph walks. The "commit-graph" file is
3195 stored either in the .git/objects/info directory or in the info
3196 directory of an alternate object database.
3199 particular <a class="link" href="#def_revision">revision</a>, such as <a class="link" href="#def_parent">parents</a>, committer,
3202 revision.
3203 </dd><dt><span class="term"><a name="def_commit-ish"></a>commit-ish (also committish)</span></dt><dd>
3204 A <a class="link" href="#def_commit_object">commit object</a> or an <a class="link" href="#def_object">object</a> that
3205 can be recursively <a class="link" href="#def_dereference">dereferenced</a> to a commit object.
3206 The following are all commit-ishes:
3207 a commit object,
3209 object,
3210 a tag object that points to a tag object that points to a
3211 commit object,
3212 etc.
3214 Fundamental data structures and utilities of Git. Exposes only limited
3215 source code management tools.
3217 Directed acyclic graph. The <a class="link" href="#def_commit_object">commit objects</a> form a
3218 directed acyclic graph, because they have parents (directed), and the
3224 dangling object has no references to it from any
3225 reference or <a class="link" href="#def_object">object</a> in the <a class="link" href="#def_repository">repository</a>.
3227 <p class="simpara">Referring to a <a class="link" href="#def_symref">symbolic ref</a>: the action of accessing the
3229 dereferencing involves repeating the aforementioned process on the
3230 resulting ref until a non-symbolic reference is found.</p>
3231 <p class="simpara">Referring to a <a class="link" href="#def_tag_object">tag object</a>: the action of accessing the
3232 <a class="link" href="#def_object">object</a> a tag points at. Tags are recursively dereferenced by
3233 repeating the operation on the result object until the result has either a
3234 specified <a class="link" href="#def_object_type">object type</a> (where applicable) or any non-"tag"
3235 object type. A synonym for "recursive dereference" in the context of tags is
3237 <p class="simpara">Referring to a <a class="link" href="#def_commit_object">commit object</a>: the action of accessing
3238 the commit’s tree object. Commits cannot be dereferenced recursively.</p>
3239 <p class="simpara">Unless otherwise specified, "dereferencing" as it used in the context of Git
3240 commands or protocols is implicitly recursive.</p>
3244 history HEAD represents operate on the history leading to the
3245 tip of the branch the HEAD points at. However, Git also
3248 particular branch. The HEAD in such a state is called
3251 (e.g. <code class="literal">git</code> <code class="literal">commit</code> to build a new history on top of it) still work
3252 while the HEAD is detached. They update the HEAD to point at the tip
3253 of the updated history without affecting any branch. Commands that
3254 update or inquire information <span class="emphasis"><em>about</em></span> the current branch (e.g. <code class="literal">git</code>
3255 <code class="literal">branch</code> <code class="literal">--set-upstream-to</code> that sets what remote-tracking branch the
3256 current branch integrates with) obviously do not work, as there is no
3257 (real) current branch to ask about in this state.</p>
3259 The list you get with "ls" :-)
3262 it contains modifications which have not been <a class="link" href="#def_commit">committed</a> to the current
3268 A fast-forward is a special type of <a class="link" href="#def_merge">merge</a> where you have a
3272 <a class="link" href="#def_commit">commit</a> but instead just update your branch to point at the same
3273 revision as the branch you are merging. This will happen frequently on a
3281 and to get them, too. See also <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
3283 Linus Torvalds originally designed Git to be a user space file system,
3284 i.e. the infrastructure to hold files and directories. That ensured the
3285 efficiency and speed of Git.
3290 points at the directory that is the real repository.
3291 For proper use see <a class="ulink" href="git-worktree.html" target="_top">git-worktree(1)</a> or <a class="ulink" href="git-submodule.html" target="_top">git-submodule(1)</a>.
3292 For syntax see <a class="ulink" href="gitrepository-layout.html" target="_top">gitrepository-layout(5)</a>.
3295 together by recording fake ancestry information for commits. This way
3296 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
3297 is different from what was recorded when the commit was
3300 transferring objects between repositories; see <a class="ulink" href="git-replace.html" target="_top">git-replace(1)</a>
3301 for a more flexible and robust system to do the same thing.</p>
3305 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
3307 <code class="literal">$GIT_DIR/refs/heads/</code> directory, except when using packed refs. (See
3310 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
3311 referred to by HEAD. HEAD is a reference to one of the
3314 references an arbitrary commit.
3318 During the normal execution of several Git commands, call-outs are made
3319 to optional scripts that allow a developer to add functionality or
3320 checking. Typically, the hooks allow for a command to be pre-verified
3321 and potentially aborted, and allow for a post-notification after the
3322 operation is done. The hook scripts are found in the
3324 removing the .<code class="literal">sample</code> suffix from the filename. In earlier versions
3325 of Git you had to make them executable.
3327 A collection of files with stat information, whose contents are stored
3328 as objects. The index is a stored version of your
3329 <a class="link" href="#def_working_tree">working tree</a>. Truth be told, it can also contain a second, and even
3330 a third version of a working tree, which are used
3333 The information regarding a particular file, stored in the
3336 the index contains multiple versions of that file).
3340 "master" is created, and becomes the active branch. In most
3341 cases, this contains the local development, though that is
3342 purely by convention and is not required.
3347 case where the merged-in branch is from a different repository,
3349 and then merging the result into the current branch. This
3350 combination of fetch and merge operations is called a
3352 that identifies changes made since the branches diverged, and
3353 then applies all those changes together. In cases where changes
3354 conflict, manual intervention may be required to complete the
3355 merge.</p>
3356 <p class="simpara">As a noun: unless it is a <a class="link" href="#def_fast_forward">fast-forward</a>, a
3357 successful merge results in the creation of a new <a class="link" href="#def_commit">commit</a>
3358 representing the result of the merge, and having as
3359 <a class="link" href="#def_parent">parents</a> the tips of the merged <a class="link" href="#def_branch">branches</a>.
3360 This commit is referred to as a "merge commit", or sometimes just a
3363 The unit of storage in Git. It is uniquely identified by the
3365 object cannot be changed.
3370 </dd><dt><span class="term"><a name="def_object_identifier"></a>object identifier (oid)</span></dt><dd>
3374 object name is usually represented by a 40 character
3378 "<a class="link" href="#def_tree_object">tree</a>", "<a class="link" href="#def_tag_object">tag</a>" or
3382 To <a class="link" href="#def_merge">merge</a> more than two <a class="link" href="#def_branch">branches</a>.
3386 such an operation, the commit first created becomes a commit
3387 without a parent, starting a new history.
3390 at least one upstream project which they track. By default
3392 will be fetched into <a class="link" href="#def_remote_tracking_branch">remote-tracking branches</a> named
3393 origin/name-of-upstream-branch, which you can see using
3394 <code class="literal">git</code> <code class="literal">branch</code> <code class="literal">-r</code>.
3396 Only update and add files to the working directory, but don’t
3397 delete them, similar to how <span class="emphasis"><em>cp -R</em></span> would update the contents
3398 in the destination directory. This is the default mode in a
3400 <a class="link" href="#def_index">index</a> or a <a class="link" href="#def_tree-ish">tree-ish</a>. In
3401 contrast, no-overlay mode also deletes tracked files not
3404 A set of objects which have been compressed into one file (to save space
3405 or to transmit them efficiently).
3407 The list of identifiers, and other information, of the objects in a
3408 <a class="link" href="#def_pack">pack</a>, to assist in efficiently accessing the contents of a
3409 pack.
3414 and many other commands to
3415 limit the scope of operations to some subset of the tree or
3416 working tree. See the documentation of each command for whether
3417 paths are relative to the current directory or toplevel. The
3418 pathspec syntax is as follows:</p>
3419 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3420 any path matches itself
3422 the pathspec up to the last slash represents a
3423 directory prefix. The scope of that pathspec is
3424 limited to that subtree.
3426 the rest of the pathspec is a pattern for the remainder
3427 of the pathname. Paths relative to the directory
3428 prefix will be matched against that pattern using fnmatch(3);
3429 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.
3430 </li></ul></div>
3432 in the Documentation subtree,
3433 including Documentation/chapter_1/figure_1.jpg.</p>
3434 <p class="simpara">A pathspec that begins with a colon <code class="literal">:</code> has special meaning. In the
3435 short form, the leading colon <code class="literal">:</code> is followed by zero or more "magic
3436 signature" letters (which optionally is terminated by another colon <code class="literal">:</code>),
3437 and the remainder is the pattern to match against the path.
3438 The "magic signature" consists of ASCII symbols that are neither
3439 alphanumeric, glob, regex special characters nor colon.
3440 The optional colon that terminates the "magic signature" can be
3441 omitted if the pattern begins with a character that does not belong to
3443 <p class="simpara">In the long form, the leading colon <code class="literal">:</code> is followed by an open
3444 parenthesis (, a comma-separated list of zero or more "magic words",
3445 and a close parentheses ), and the remainder is the pattern to match
3446 against the path.</p>
3448 should not be combined with other pathspec.</p>
3450 The magic word <code class="literal">top</code> (magic signature: <code class="literal">/</code>) makes the pattern
3451 match from the root of the working tree, even when you are
3452 running the command from inside a subdirectory.
3454 Wildcards in the pattern such as * or ? are treated
3455 as literal characters.
3457 Case insensitive match.
3460 consumption by fnmatch(3) with the FNM_PATHNAME flag:
3461 wildcards in the pattern will not match a / in the pathname.
3462 For example, "Documentation/*.html" matches
3466 full pathname may have special meaning:</p>
3467 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3468 A leading "**" followed by a slash means match in all
3469 directories. For example, "**/foo" matches file or directory
3470 "<code class="literal">foo</code>" anywhere, the same as pattern "<code class="literal">foo</code>". "**/foo/bar"
3478 A slash followed by two consecutive asterisks then a slash
3480 matches "<code class="literal">a/b</code>", "<code class="literal">a/x/b</code>", "<code class="literal">a/x/y/b</code>" and so on.
3484 </li></ul></div>
3486 <p class="simpara">After <code class="literal">attr:</code> comes a space separated list of "attribute
3487 requirements", all of which must be met in order for the
3488 path to be considered a match; this is in addition to the
3489 usual non-magic pathspec pattern matching.
3492 these forms:</p>
3493 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3494 "<code class="literal">ATTR</code>" requires that the attribute <code class="literal">ATTR</code> be set.
3496 "<code class="literal">-ATTR</code>" requires that the attribute <code class="literal">ATTR</code> be unset.
3498 "<code class="literal">ATTR=VALUE</code>" requires that the attribute <code class="literal">ATTR</code> be
3502 unspecified.</p>
3504 obtained from working tree, not from the given tree object.</p>
3505 </li></ul></div>
3507 After a path matches any non-exclude pathspec, it will be run
3508 through all exclude pathspecs (magic signature: ! or its
3510 is no non-exclude pathspec, the exclusion is applied to the
3511 result set as if invoked without any pathspec.
3512 </dd></dl></div>
3515 of the logical predecessor(s) in the line of development, i.e. its
3516 parents.
3522 routines that help select changes that add or delete a given text
3523 string. With the <code class="literal">--pickaxe-all</code> option, it can be used to view the full
3525 particular line of text. See <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>.
3529 Cute name for programs and program suites depending on
3533 </dd><dt><span class="term"><a name="def_per_worktree_ref"></a>per-worktree ref</span></dt><dd>
3537 unusual refs.
3540 read via normal Git commands, but cannot be written to by commands like
3543 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3544 <code class="literal">FETCH_HEAD</code> is written by <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> or <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>. It
3545 may refer to multiple object IDs. Each object ID is annotated with metadata
3546 indicating where it was fetched from and its fetch status.
3548 <code class="literal">MERGE_HEAD</code> is written by <a class="ulink" href="git-merge.html" target="_top">git-merge(1)</a> when resolving merge
3549 conflicts. It contains all commit IDs which are being merged.
3550 </li></ul></div>
3552 Pulling a <a class="link" href="#def_branch">branch</a> means to <a class="link" href="#def_fetch">fetch</a> it and
3553 <a class="link" href="#def_merge">merge</a> it. See also <a class="ulink" href="git-pull.html" target="_top">git-pull(1)</a>.
3556 <a class="link" href="#def_head_ref">head ref</a> from a remote <a class="link" href="#def_repository">repository</a>,
3557 find out if it is an ancestor to the branch’s local
3558 head ref, and in that case, putting all
3560 head ref, and which are missing from the remote
3561 repository, into the remote
3564 ancestor to the local head, the push fails.
3567 "reachable" from that commit. More
3569 another if we can reach the one from the other by a <a class="link" href="#def_chain">chain</a>
3572 <a class="link" href="#def_tree_object">trees</a> to the trees or <a class="link" href="#def_blob_object">blobs</a>
3573 that they contain.
3574 </dd><dt><span class="term"><a name="def_reachability_bitmap"></a>reachability bitmaps</span></dt><dd>
3575 Reachability bitmaps store information about the
3577 a packfile, or a multi-pack index (MIDX), to speed up object search.
3578 The bitmaps are stored in a ".bitmap" file. A repository may have at
3579 most one bitmap file in use. The bitmap file may belong to either one
3580 pack, or the repository’s multi-pack index (if it exists).
3584 to the result.
3586 <p class="simpara">A name that points to an <a class="link" href="#def_object_name">object name</a> or
3588 For convenience, a ref can sometimes be abbreviated when used
3589 as an argument to a Git command; see <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>
3590 for details.
3593 Ref names must either start with <code class="literal">refs/</code> or be located in the root of
3594 the hierarchy. For the latter, their name must follow these rules:</p>
3595 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3596 The name consists of only upper-case characters or underscores.
3598 <p class="simpara">The name ends with "<code class="literal">_HEAD</code>" or is equal to "<code class="literal">HEAD</code>".</p>
3600 match these rules. The following list is exhaustive and shall not be
3601 extended in the future:</p>
3613 the <code class="literal">refs/heads/</code> hierarchy is used to represent local branches whereas
3615 </li></ul></div>
3617 A reflog shows the local "history" of a ref. In other words,
3618 it can tell you what the 3rd last revision in <span class="emphasis"><em>this</em></span> repository
3620 yesterday 9:14pm. See <a class="ulink" href="git-reflog.html" target="_top">git-reflog(1)</a> for details.
3624 <a class="link" href="#def_ref">ref</a> and local ref. See <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a> or
3628 project but resides somewhere else. To communicate with remotes,
3630 </dd><dt><span class="term"><a name="def_remote_tracking_branch"></a>remote-tracking branch</span></dt><dd>
3633 <span class="emphasis"><em>refs/remotes/foo/bar</em></span> (indicating that it tracks a branch named
3634 <span class="emphasis"><em>bar</em></span> in a remote named <span class="emphasis"><em>foo</em></span>), and matches the right-hand-side of
3636 branch should not contain direct modifications or have local
3637 commits made to it.
3642 accompanied by meta data from one or more <a class="link" href="#def_porcelain">porcelains</a>. A
3643 repository can share an object database with other repositories
3646 The action of fixing up manually what a failed automatic
3651 To throw away part of the development, i.e. to assign the
3652 <a class="link" href="#def_head">head</a> to an earlier <a class="link" href="#def_revision">revision</a>.
3654 Source code management (tool).
3656 "Secure Hash Algorithm 1"; a cryptographic hash function.
3657 In the context of Git used as a synonym for <a class="link" href="#def_object_name">object name</a>.
3660 but the phrase makes it more explicit that it was created by
3661 running <code class="literal">git</code> <code class="literal">clone</code> <code class="literal">--depth=..</code>. command.
3662 </dd><dt><span class="term"><a name="def_shallow_repository"></a>shallow repository</span></dt><dd>
3664 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
3665 words, Git is told to pretend that these commits do not have the
3667 object</a>). This is sometimes useful when you are interested only in the
3668 recent history of a project even though the real history recorded in the
3669 upstream is much larger. A shallow repository
3670 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
3671 its history can be later deepened with <a class="ulink" href="git-fetch.html" target="_top">git-fetch(1)</a>.
3677 separate project inside another repository (the latter of
3682 The superproject knows about the names of (but does not hold
3683 copies of) commit objects of the contained submodules.
3686 itself, it is of the format <span class="emphasis"><em>ref: refs/some/thing</em></span> and when referenced,
3688 <span class="emphasis"><em><a class="link" href="#def_HEAD">HEAD</a></em></span> is a prime example of a symref. Symbolic references
3689 are manipulated with the <a class="ulink" href="git-symbolic-ref.html" target="_top">git-symbolic-ref(1)</a> command.
3691 A <a class="link" href="#def_ref">ref</a> under <code class="literal">refs/tags/</code> namespace that points to an
3692 object of an arbitrary type (typically a tag points to either a
3693 <a class="link" href="#def_tag_object">tag</a> or a <a class="link" href="#def_commit_object">commit object</a>).
3697 in Git’s context). A tag is most typically used to mark a particular
3700 An <a class="link" href="#def_object">object</a> containing a <a class="link" href="#def_ref">ref</a> pointing to
3701 another object, which can contain a message just like a
3703 signature, in which case it is called a "signed tag object".
3706 identify a conceptual line of development. Since branches are very easy
3707 and inexpensive, it is often desirable to have several small branches
3708 that each contain very well defined concepts or small incremental yet
3709 related changes.
3711 Either a <a class="link" href="#def_working_tree">working tree</a>, or a <a class="link" href="#def_tree_object">tree
3712 object</a> together with the dependent <a class="link" href="#def_blob_object">blob</a> and tree objects
3713 (i.e. a stored representation of a working tree).
3715 An <a class="link" href="#def_object">object</a> containing a list of file names and modes along
3716 with refs to the associated blob and/or tree objects. A
3717 <a class="link" href="#def_tree">tree</a> is equivalent to a <a class="link" href="#def_directory">directory</a>.
3719 A <a class="link" href="#def_tree_object">tree object</a> or an <a class="link" href="#def_object">object</a> that can
3724 The following are all tree-ishes:
3726 a tree object,
3728 a tag object that points to a tag object that points to a tree
3729 object,
3730 etc.
3732 The <a class="link" href="#def_HEAD">HEAD</a> can point at a <a class="link" href="#def_branch">branch</a>
3733 that does not yet exist and that does not have any commit on
3734 it yet, and such a branch is called an unborn branch. The
3735 most typical way users encounter an unborn branch is by
3736 creating a repository anew without cloning from elsewhere.
3737 The HEAD would point at the <span class="emphasis"><em>main</em></span> (or <span class="emphasis"><em>master</em></span>, depending
3738 on your configuration) branch that is yet to be born. Also
3739 some operations can get you on an unborn branch with their
3744 </dd><dt><span class="term"><a name="def_unreachable_object"></a>unreachable object</span></dt><dd>
3745 An <a class="link" href="#def_object">object</a> which is not <a class="link" href="#def_reachable">reachable</a> from a
3746 <a class="link" href="#def_branch">branch</a>, <a class="link" href="#def_tag">tag</a>, or any other reference.
3749 question (or the branch in question is rebased onto). It is configured
3751 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>".
3753 The tree of actual checked out files. The working tree normally
3755 plus any local changes that you have made but not yet committed.
3757 A repository can have zero (i.e. bare repository) or one or
3758 more worktrees attached to it. One "worktree" consists of a
3759 "working tree" and repository metadata, most of which are
3760 shared among other worktrees of a single repository, and
3761 some of which are maintained separately per worktree
3762 (e.g. the index, HEAD and pseudorefs like MERGE_HEAD,
3763 per-worktree refs and per-worktree configuration file).
3764 </dd></dl></div>
3765 </div>
3766 </div>
3767 <div class="appendix"><div class="titlepage"><div><div><h1 class="title"><a name="git-quick-start"></a>Appendix A. Git Quick Reference</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><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>
3769 <p>This is a quick summary of the major commands; the previous chapters
3770 explain how these work in more detail.</p>
3771 <div class="section"><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>
3775 $ cd project
3776 $ git init
3777 Initialized empty Git repository in .git/
3778 $ git add .
3779 $ git commit</pre>
3782 $ cd project</pre>
3783 </div>
3784 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="managing-branches"></a>Managing branches</h2></div></div></div>
3787 $ git switch test # switch working directory to branch "test"
3788 $ git branch new # create branch "new" starting at current HEAD
3793 $ git branch new HEAD^ # commit before the most recent
3794 $ git branch new HEAD^^ # commit before that
3800 $ git branch -r # list
3801 origin/master
3802 origin/next
3803 ...
3804 $ git switch -c masterwork origin/master</pre>
3805 <p>Fetch a branch from a different repository, and give it a new
3806 name in your repository:</p>
3811 $ git remote # list remote repositories
3812 example
3813 origin
3814 $ git remote show example # get details
3815 * remote example
3816 URL: git://example.com/project.git
3817 Tracked remote branches
3818 master
3819 next
3820 ...
3821 $ git fetch example # update branches from example
3822 $ git branch -r # list all remote branches</pre>
3823 </div>
3824 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="exploring-history"></a>Exploring history</h2></div></div></div>
3827 $ git log # list all commits
3828 $ git log src/ # ...modifying src/
3830 $ git log master..test # ...in branch test, not in branch master
3831 $ git log test..master # ...in branch master, but not in test
3832 $ git log test...master # ...in one branch, not in both
3833 $ git log -S'foo()' # ...where difference contain "foo()"
3835 $ git log -p # show patches as well
3836 $ git show # most recent commit
3838 $ git diff v2.6.15..HEAD # diff with current head
3844 $ git bisect bad # current version is bad
3845 $ git bisect good v2.6.13-rc2 # last known good revision
3846 Bisecting: 675 revisions left to test after this
3847 # test here, then:
3848 $ git bisect good # if this revision is good, or
3849 $ git bisect bad # if this revision is bad.
3850 # repeat until done.</pre>
3851 </div>
3852 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="making-changes"></a>Making changes</h2></div></div></div>
3856 [user]
3857 name = Your Name Comes Here
3858 email = you@yourdomain.example.com
3859 EOF</pre>
3860 <p>Select file contents to include in the next commit, then make the
3861 commit:</p>
3863 $ git add b.txt # new file
3864 $ git rm c.txt # old file
3865 $ git commit</pre>
3868 $ git commit -a # use latest content of all tracked files</pre>
3869 </div>
3870 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="merging"></a>Merging</h2></div></div></div>
3873 $ git pull git://example.com/project.git master
3874 # fetch and merge in remote branch
3875 $ git pull . test # equivalent to git merge test</pre>
3876 </div>
3877 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sharing-your-changes"></a>Sharing your changes</h2></div></div></div>
3881 # in HEAD but not in origin
3883 <p>Fetch a branch in a different Git repository, then merge into the
3884 current branch:</p>
3886 <p>Store the fetched branch into a local branch before merging into the
3887 current branch:</p>
3889 <p>After creating commits on a local branch, update the remote
3890 branch with your commits:</p>
3896 $ git push example test</pre>
3897 </div>
3898 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="repository-maintenance"></a>Repository maintenance</h2></div></div></div>
3904 </div>
3905 </div>
3906 <div class="appendix"><div class="titlepage"><div><div><h1 class="title"><a name="todo"></a>Appendix B. Notes and todo list for this manual</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></div>
3908 <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="todo-list"></a>Todo list</h2></div></div></div>
3912 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3913 It must be readable in order, from beginning to end, by someone
3914 intelligent with a basic grasp of the UNIX command line, but without
3915 any special knowledge of Git. If necessary, any other prerequisites
3916 should be specifically mentioned as they arise.
3918 Whenever possible, section headings should clearly describe the task
3919 they explain how to do, in language that requires no more knowledge
3920 than necessary: for example, "importing patches into a project" rather
3922 </li></ul></div>
3923 <p>Think about how to create a clear chapter dependency graph that will
3924 allow people to get to important topics without necessarily reading
3925 everything in between.</p>
3926 <p>Scan <code class="literal">Documentation/</code> for other stuff left out; in particular:</p>
3927 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
3928 howto’s
3932 hooks
3935 </li></ul></div>
3937 <p>Scan man pages to see if any assume more background than this manual
3938 provides.</p>
3939 <p>Add more good examples. Entire sections of just cookbook examples
3940 might be a good idea; maybe make an "advanced examples" section a
3941 standard end-of-chapter section?</p>
3943 <p>Add a section on working with other version control systems, including
3944 CVS, Subversion, and just imports of series of release tarballs.</p>
3947 <p>More on recovery from repository corruption. See:
3948 <a class="ulink" href="https://lore.kernel.org/git/Pine.LNX.4.64.0702272039540.12485@woody.linux-foundation.org/" target="_top">https://lore.kernel.org/git/Pine.LNX.4.64.0702272039540.12485@woody.linux-foundation.org/</a>
3949 <a class="ulink" href="https://lore.kernel.org/git/Pine.LNX.4.64.0702141033400.3604@woody.linux-foundation.org/" target="_top">https://lore.kernel.org/git/Pine.LNX.4.64.0702141033400.3604@woody.linux-foundation.org/</a></p>
3950 </div>
3951 </div>
3952 </div></body></html>