tea-test-dao

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Git User Manual</title><link rel="stylesheet" type="text/css" href="docbook-xsl.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div lang="en" class="book"><div class="titlepage"><div><div><h1 class="title"><a name="id-1"></a>Git User Manual</h1></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="preface"><a href="#_introduction">Introduction</a></span></dt><dt><span class="chapter"><a href="#repositories-and-branches">1. Repositories and Branches</a></span></dt><dd><dl><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="#exploring-git-history">2. Exploring Git history</a></span></dt><dd><dl><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#Developing-With-git">3. Developing with Git</a></span></dt><dd><dl><dt><span class="section"><a href="#telling-git-your-name">Telling Git your name</a></span></dt><dt><span class="section"><a href="#creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#how-to-make-a-commit">How to make a commit</a></span></dt><dt><span class="section"><a href="#creating-good-commit-messages">Creating good commit messages</a></span></dt><dt><span class="section"><a href="#ignoring-files">Ignoring files</a></span></dt><dt><span class="section"><a href="#how-to-merge">How to merge</a></span></dt><dt><span class="section"><a href="#resolving-a-merge">Resolving a merge</a></span></dt><dd><dl><dt><span class="section"><a href="#conflict-resolution">Getting conflict-resolution help during a merge</a></span></dt></dl></dd><dt><span class="section"><a href="#undoing-a-merge">Undoing a merge</a></span></dt><dt><span class="section"><a href="#fast-forwards">Fast-forward merges</a></span></dt><dt><span class="section"><a href="#fixing-mistakes">Fixing mistakes</a></span></dt><dd><dl><dt><span class="section"><a href="#reverting-a-commit">Fixing a mistake with a new commit</a></span></dt><dt><span class="section"><a href="#fixing-a-mistake-by-rewriting-history">Fixing a mistake by rewriting history</a></span></dt><dt><span class="section"><a href="#checkout-of-path">Checking out an old version of a file</a></span></dt><dt><span class="section"><a href="#interrupted-work">Temporarily setting aside work in progress</a></span></dt></dl></dd><dt><span class="section"><a href="#ensuring-good-performance">Ensuring good performance</a></span></dt><dt><span class="section"><a href="#ensuring-reliability">Ensuring reliability</a></span></dt><dd><dl><dt><span class="section"><a href="#checking-for-corruption">Checking the repository for corruption</a></span></dt><dt><span class="section"><a href="#recovering-lost-changes">Recovering lost changes</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#sharing-development">4. Sharing development with others</a></span></dt><dd><dl><dt><span class="section"><a href="#getting-updates-With-git-pull">Getting updates with git pull</a></span></dt><dt><span class="section"><a href="#submitting-patches">Submitting patches to a project</a></span></dt><dt><span class="section"><a href="#importing-patches">Importing patches to a project</a></span></dt><dt><span class="section"><a href="#public-repositories">Public Git repositories</a></span></dt><dd><dl><dt><span class="section"><a href="#setting-up-a-public-repository">Setting up a public repository</a></span></dt><dt><span class="section"><a href="#exporting-via-git">Exporting a Git repository via the Git protocol</a></span></dt><dt><span class="section"><a href="#exporting-via-http">Exporting a git repository via HTTP</a></span></dt><dt><span class="section"><a href="#pushing-changes-to-a-public-repository">Pushing changes to a public repository</a></span></dt><dt><span class="section"><a href="#forcing-push">What to do when a push fails</a></span></dt><dt><span class="section"><a href="#setting-up-a-shared-repository">Setting up a shared repository</a></span></dt><dt><span class="section"><a href="#setting-up-gitweb">Allowing web browsing of a repository</a></span></dt></dl></dd><dt><span class="section"><a href="#how-to-get-a-git-repository-with-minimal-history">How to get a Git repository with minimal history</a></span></dt><dt><span class="section"><a href="#sharing-development-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#maintaining-topic-branches">Maintaining topic branches for a Linux subsystem maintainer</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#cleaning-up-history">5. Rewriting history and maintaining patch series</a></span></dt><dd><dl><dt><span class="section"><a href="#patch-series">Creating the perfect patch series</a></span></dt><dt><span class="section"><a href="#using-git-rebase">Keeping a patch series up to date using git rebase</a></span></dt><dt><span class="section"><a href="#rewriting-one-commit">Rewriting a single commit</a></span></dt><dt><span class="section"><a href="#reordering-patch-series">Reordering or selecting from a patch series</a></span></dt><dt><span class="section"><a href="#interactive-rebase">Using interactive rebases</a></span></dt><dt><span class="section"><a href="#patch-series-tools">Other tools</a></span></dt><dt><span class="section"><a href="#problems-With-rewriting-history">Problems with rewriting history</a></span></dt><dt><span class="section"><a href="#bisect-merges">Why bisecting merge commits can be harder than bisecting linear history</a></span></dt></dl></dd><dt><span class="chapter"><a href="#advanced-branch-management">6. Advanced branch management</a></span></dt><dd><dl><dt><span class="section"><a href="#fetching-individual-branches">Fetching individual branches</a></span></dt><dt><span class="section"><a href="#fetch-fast-forwards">git fetch and fast-forwards</a></span></dt><dt><span class="section"><a href="#forcing-fetch">Forcing git fetch to do non-fast-forward updates</a></span></dt><dt><span class="section"><a href="#remote-branch-configuration">Configuring remote-tracking branches</a></span></dt></dl></dd><dt><span class="chapter"><a href="#git-concepts">7. Git concepts</a></span></dt><dd><dl><dt><span class="section"><a href="#the-object-database">The Object Database</a></span></dt><dd><dl><dt><span class="section"><a href="#commit-object">Commit Object</a></span></dt><dt><span class="section"><a href="#tree-object">Tree Object</a></span></dt><dt><span class="section"><a href="#blob-object">Blob Object</a></span></dt><dt><span class="section"><a href="#trust">Trust</a></span></dt><dt><span class="section"><a href="#tag-object">Tag Object</a></span></dt><dt><span class="section"><a href="#pack-files">How Git stores objects efficiently: pack files</a></span></dt><dt><span class="section"><a href="#dangling-objects">Dangling objects</a></span></dt><dt><span class="section"><a href="#recovering-from-repository-corruption">Recovering from repository corruption</a></span></dt></dl></dd><dt><span class="section"><a href="#the-index">The index</a></span></dt></dl></dd><dt><span class="chapter"><a href="#submodules">8. Submodules</a></span></dt><dd><dl><dt><span class="section"><a href="#pitfalls-with-submodules">Pitfalls with submodules</a></span></dt></dl></dd><dt><span class="chapter"><a href="#low-level-operations">9. Low-level Git operations</a></span></dt><dd><dl><dt><span class="section"><a href="#object-manipulation">Object access and manipulation</a></span></dt><dt><span class="section"><a href="#the-workflow">The Workflow</a></span></dt><dd><dl><dt><span class="section"><a href="#working-directory-to-index">working directory → index</a></span></dt><dt><span class="section"><a href="#index-to-object-database">index → object database</a></span></dt><dt><span class="section"><a href="#object-database-to-index">object database → index</a></span></dt><dt><span class="section"><a href="#index-to-working-directory">index → working directory</a></span></dt><dt><span class="section"><a href="#tying-it-all-together">Tying it all together</a></span></dt></dl></dd><dt><span class="section"><a href="#examining-the-data">Examining the data</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees">Merging multiple trees</a></span></dt><dt><span class="section"><a href="#merging-multiple-trees-2">Merging multiple trees, continued</a></span></dt></dl></dd><dt><span class="chapter"><a href="#hacking-git">10. Hacking Git</a></span></dt><dd><dl><dt><span class="section"><a href="#object-details">Object storage format</a></span></dt><dt><span class="section"><a href="#birdview-on-the-source-code">A birds-eye view of Git’s source code</a></span></dt></dl></dd><dt><span class="chapter"><a href="#glossary">11. Git Glossary</a></span></dt><dd><dl><dt><span class="section"><a href="#git-explained">Git explained</a></span></dt></dl></dd><dt><span class="appendix"><a href="#git-quick-start">A. Git Quick Reference</a></span></dt><dd><dl><dt><span class="section"><a href="#quick-creating-a-new-repository">Creating a new repository</a></span></dt><dt><span class="section"><a href="#managing-branches">Managing branches</a></span></dt><dt><span class="section"><a href="#exploring-history">Exploring history</a></span></dt><dt><span class="section"><a href="#making-changes">Making changes</a></span></dt><dt><span class="section"><a href="#merging">Merging</a></span></dt><dt><span class="section"><a href="#sharing-your-changes">Sharing your changes</a></span></dt><dt><span class="section"><a href="#repository-maintenance">Repository maintenance</a></span></dt></dl></dd><dt><span class="appendix"><a href="#todo">B. Notes and todo list for this manual</a></span></dt><dd><dl><dt><span class="section"><a href="#todo-list">Todo list</a></span></dt></dl></dd></dl></div> <div class="preface"><div class="titlepage"><div><div><h1 class="title"><a name="_introduction"></a>Introduction</h1></div></div></div> <p>Git is a fast distributed revision control system.</p> <p>This manual is designed to be readable by someone with basic UNIX command-line skills, but no previous knowledge of Git.</p> <p><a class="xref" href="#repositories-and-branches" title="Chapter 1. Repositories and Branches">Chapter 1, <i>Repositories and Branches</i></a> and <a class="xref" href="#exploring-git-history" title="Chapter 2. Exploring Git history">Chapter 2, <i>Exploring Git history</i></a> explain how to fetch and study a project using git—read these chapters to learn how to build and test a particular version of a software project, search for regressions, and so on.</p> <p>People needing to do actual development will also want to read <a class="xref" href="#Developing-With-git" title="Chapter 3. Developing with Git">Chapter 3, <i>Developing with Git</i></a> and <a class="xref" href="#sharing-development" title="Chapter 4. Sharing development with others">Chapter 4, <i>Sharing development with others</i></a>.</p> <p>Further chapters cover more specialized topics.</p> <p>Comprehensive reference documentation is available through the man pages, or <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> command. For example, for the command <code class="literal">git clone <repo></code>, you can either use:</p> <pre class="screen">$ man git-clone</pre> <p>or:</p> <pre class="screen">$ git help clone</pre> <p>With the latter, you can use the manual viewer of your choice; see <a class="ulink" href="git-help.html" target="_top">git-help(1)</a> for more information.</p> <p>See also <a class="xref" href="#git-quick-start" title="Appendix A. Git Quick Reference">Appendix A, <i>Git Quick Reference</i></a> for a brief overview of Git commands, without any explanation.</p> <p>Finally, see <a class="xref" href="#todo" title="Appendix B. Notes and todo list for this manual">Appendix B, <i>Notes and todo list for this manual</i></a> for ways that you can help make this manual more complete.</p> </div> <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="repositories-and-branches"></a>Chapter 1. Repositories and Branches</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#how-to-get-a-git-repository">How to get a Git repository</a></span></dt><dt><span class="section"><a href="#how-to-check-out">How to check out a different version of a project</a></span></dt><dt><span class="section"><a href="#understanding-commits">Understanding History: Commits</a></span></dt><dd><dl><dt><span class="section"><a href="#understanding-reachability">Understanding history: commits, parents, and reachability</a></span></dt><dt><span class="section"><a href="#history-diagrams">Understanding history: History diagrams</a></span></dt><dt><span class="section"><a href="#what-is-a-branch">Understanding history: What is a branch?</a></span></dt></dl></dd><dt><span class="section"><a href="#manipulating-branches">Manipulating branches</a></span></dt><dt><span class="section"><a href="#detached-head">Examining an old version without creating a new branch</a></span></dt><dt><span class="section"><a href="#examining-remote-branches">Examining branches from a remote repository</a></span></dt><dt><span class="section"><a href="#how-git-stores-references">Naming branches, tags, and other references</a></span></dt><dt><span class="section"><a href="#Updating-a-repository-With-git-fetch">Updating a repository with git fetch</a></span></dt><dt><span class="section"><a href="#fetching-branches">Fetching branches from other repositories</a></span></dt></dl></div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-get-a-git-repository"></a>How to get a Git repository</h2></div></div></div> <p>It will be useful to have a Git repository to experiment with as you read this manual.</p> <p>The best way to get one is by using the <a class="ulink" href="git-clone.html" target="_top">git-clone(1)</a> command to download a copy of an existing repository. If you don’t already have a project in mind, here are some interesting examples:</p> <pre class="screen"> # Git itself (approx. 40MB download): $ git clone git://git.kernel.org/pub/scm/git/git.git # the Linux kernel (approx. 640MB download): $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git</pre> <p>The initial clone may be time-consuming for a large project, but you will only need to clone once.</p> <p>The clone command creates a new directory named after the project (<code class="literal">git</code> or <code class="literal">linux</code> in the examples above). After you cd into this directory, you will see that it contains a copy of the project files, called the <a class="link" href="#def_working_tree">working tree</a>, together with a special top-level directory named <code class="literal">.git</code>, which contains all the information about the history of the project.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-to-check-out"></a>How to check out a different version of a project</h2></div></div></div> <p>Git is best thought of as a tool for storing the history of a collection of files. It stores the history as a compressed collection of interrelated snapshots of the project’s contents. In Git each such version is called a <a class="link" href="#def_commit">commit</a>.</p> <p>Those snapshots aren’t necessarily all arranged in a single line from oldest to newest; instead, work may simultaneously proceed along parallel lines of development, called <a class="link" href="#def_branch">branches</a>, which may merge and diverge.</p> <p>A single Git repository can track development on multiple branches. It does this by keeping a list of <a class="link" href="#def_head">heads</a> which reference the latest commit on each branch; the <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> command shows you the list of branch heads:</p> <pre class="screen">$ git branch * master</pre> <p>A freshly cloned repository contains a single branch head, by default named "master", with the working directory initialized to the state of the project referred to by that branch head.</p> <p>Most projects also use <a class="link" href="#def_tag">tags</a>. Tags, like heads, are references into the project’s history, and can be listed using the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> command:</p> <pre class="screen">$ git tag -l v2.6.11 v2.6.11-tree v2.6.12 v2.6.12-rc2 v2.6.12-rc3 v2.6.12-rc4 v2.6.12-rc5 v2.6.12-rc6 v2.6.13 ...</pre> <p>Tags are expected to always point at the same version of a project, while heads are expected to advance as development progresses.</p> <p>Create a new branch head pointing to one of these versions and check it out using <a class="ulink" href="git-switch.html" target="_top">git-switch(1)</a>:</p> <pre class="screen">$ git switch -c new v2.6.13</pre> <p>The working directory then reflects the contents that the project had when it was tagged v2.6.13, and <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a> shows two branches, with an asterisk marking the currently checked-out branch:</p> <pre class="screen">$ git branch master * new</pre> <p>If you decide that you’d rather see version 2.6.17, you can modify the current branch to point at v2.6.17 instead, with</p> <pre class="screen">$ git reset --hard v2.6.17</pre> <p>Note that if the current branch head was your only reference to a particular point in history, then resetting that branch may leave you with no way to find the history it used to point to; so use this command carefully.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="understanding-commits"></a>Understanding History: Commits</h2></div></div></div> <p>Every change in the history of a project is represented by a commit. The <a class="ulink" href="git-show.html" target="_top">git-show(1)</a> command shows the most recent commit on the current branch:</p> <pre class="screen">$ git show commit 17cf781661e6d38f737f15f53ab552f1e95960d7 Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)> Date: Tue Apr 19 14:11:06 2005 -0700 Remove duplicate getenv(DB_ENVIRONMENT) call Noted by Tony Luck. diff --git a/init-db.c b/init-db.c index 65898fa..b002dc6 100644 --- a/init-db.c +++ b/init-db.c @@ -7,7 +7,7 @@ int main(int argc, char **argv) { - char *sha1_dir = getenv(DB_ENVIRONMENT), *path; + char *sha1_dir, *path; int len, i; if (mkdir(".git", 0755) < 0) {</pre> <p>As you can see, a commit shows who made the latest change, what they did, and why.</p> <p>Every commit has a 40-hexdigit id, sometimes called the "object name" or the "SHA-1 id", shown on the first line of the <code class="literal">git show</code> output. You can usually refer to a commit by a shorter name, such as a tag or a branch name, but this longer name can also be useful. Most importantly, it is a globally unique name for this commit: so if you tell somebody else the object name (for example in email), then you are guaranteed that name will refer to the same commit in their repository that it does in yours (assuming their repository has that commit at all). Since the object name is computed as a hash over the contents of the commit, you are guaranteed that the commit can never change without its name also changing.</p> <p>In fact, in <a class="xref" href="#git-concepts" title="Chapter 7. Git concepts">Chapter 7, <i>Git concepts</i></a> we shall see that everything stored in Git history, including file data and directory contents, is stored in an object with a name that is a hash of its contents.</p> <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="understanding-reachability"></a>Understanding history: commits, parents, and reachability</h3></div></div></div> <p>Every commit (except the very first commit in a project) also has a parent commit which shows what happened before this commit. Following the chain of parents will eventually take you back to the beginning of the project.</p> <p>However, the commits do not form a simple list; Git allows lines of development to diverge and then reconverge, and the point where two lines of development reconverge is called a "merge". The commit representing a merge can therefore have more than one parent, with each parent representing the most recent commit on one of the lines of development leading to that point.</p> <p>The best way to see how this works is using the <a class="ulink" href="gitk.html" target="_top">gitk(1)</a> command; running gitk now on a Git repository and looking for merge commits will help understand how Git organizes history.</p> <p>In the following, we say that commit X is "reachable" from commit Y if commit X is an ancestor of commit Y. Equivalently, you could say that Y is a descendant of X, or that there is a chain of parents leading from commit Y to commit X.</p> </div> <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="history-diagrams"></a>Understanding history: History diagrams</h3></div></div></div> <p>We will sometimes represent Git history using diagrams like the one below. Commits are shown as "o", and the links between them with lines drawn with - / and \. Time goes left to right:</p> <pre class="literallayout"> o--o--o <-- Branch A / o--o--o <-- master \ o--o--o <-- Branch B</pre> <p>If we need to talk about a particular commit, the character "o" may be replaced with another letter or number.</p> </div> <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="what-is-a-branch"></a>Understanding history: What is a branch?</h3></div></div></div> <p>When we need to be precise, we will use the word "branch" to mean a line of development, and "branch head" (or just "head") to mean a reference to the most recent commit on a branch. In the example above, the branch head named "A" is a pointer to one particular commit, but we refer to the line of three commits leading up to that point as all being part of "branch A".</p> <p>However, when no confusion will result, we often just use the term "branch" both for branches and for branch heads.</p> </div> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="manipulating-branches"></a>Manipulating branches</h2></div></div></div> <p>Creating, deleting, and modifying branches is quick and easy; here’s a summary of the commands:</p> <div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">git branch</code></span></dt><dd> list all branches. </dd><dt><span class="term"><code class="literal">git branch <branch></code></span></dt><dd> create a new branch named <code class="literal"><branch></code>, referencing the same point in history as the current branch. </dd><dt><span class="term"><code class="literal">git branch <branch> <start-point></code></span></dt><dd> create a new branch named <code class="literal"><branch></code>, referencing <code class="literal"><start-point></code>, which may be specified any way you like, including using a branch name or a tag name. </dd><dt><span class="term"><code class="literal">git branch -d <branch></code></span></dt><dd> delete the branch <code class="literal"><branch></code>; if the branch is not fully merged in its upstream branch or contained in the current branch, this command will fail with a warning. </dd><dt><span class="term"><code class="literal">git branch -D <branch></code></span></dt><dd> delete the branch <code class="literal"><branch></code> irrespective of its merged status. </dd><dt><span class="term"><code class="literal">git switch <branch></code></span></dt><dd> make the current branch <code class="literal"><branch></code>, updating the working directory to reflect the version referenced by <code class="literal"><branch></code>. </dd><dt><span class="term"><code class="literal">git switch -c <new> <start-point></code></span></dt><dd> create a new branch <code class="literal"><new></code> referencing <code class="literal"><start-point></code>, and check it out. </dd></dl></div> <p>The special symbol "HEAD" can always be used to refer to the current branch. In fact, Git uses a file named <code class="literal">HEAD</code> in the <code class="literal">.git</code> directory to remember which branch is current:</p> <pre class="screen">$ cat .git/HEAD ref: refs/heads/master</pre> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="detached-head"></a>Examining an old version without creating a new branch</h2></div></div></div> <p>The <code class="literal">git switch</code> command normally expects a branch head, but will also accept an arbitrary commit when invoked with --detach; for example, you can check out the commit referenced by a tag:</p> <pre class="screen">$ git switch --detach v2.6.17 Note: checking out 'v2.6.17'. You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another switch. If you want to create a new branch to retain commits you create, you may do so (now or later) by using -c with the switch command again. Example: git switch -c new_branch_name HEAD is now at 427abfa Linux v2.6.17</pre> <p>The HEAD then refers to the SHA-1 of the commit instead of to a branch, and git branch shows that you are no longer on a branch:</p> <pre class="screen">$ cat .git/HEAD 427abfa28afedffadfca9dd8b067eb6d36bac53f $ git branch * (detached from v2.6.17) master</pre> <p>In this case we say that the HEAD is "detached".</p> <p>This is an easy way to check out a particular version without having to make up a name for the new branch. You can still create a new branch (or tag) for this version later if you decide to.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="examining-remote-branches"></a>Examining branches from a remote repository</h2></div></div></div> <p>The "master" branch that was created at the time you cloned is a copy of the HEAD in the repository that you cloned from. That repository may also have had other branches, though, and your local repository keeps branches which track each of those remote branches, called remote-tracking branches, which you can view using the <code class="literal">-r</code> option to <a class="ulink" href="git-branch.html" target="_top">git-branch(1)</a>:</p> <pre class="screen">$ git branch -r origin/HEAD origin/html origin/maint origin/man origin/master origin/next origin/seen origin/todo</pre> <p>In this example, "origin" is called a remote repository, or "remote" for short. The branches of this repository are called "remote branches" from our point of view. The remote-tracking branches listed above were created based on the remote branches at clone time and will be updated by <code class="literal">git fetch</code> (hence <code class="literal">git pull</code>) and <code class="literal">git push</code>. See <a class="xref" href="#Updating-a-repository-With-git-fetch" title="Updating a repository with git fetch">the section called “Updating a repository with git fetch”</a> for details.</p> <p>You might want to build on one of these remote-tracking branches on a branch of your own, just as you would for a tag:</p> <pre class="screen">$ git switch -c my-todo-copy origin/todo</pre> <p>You can also check out <code class="literal">origin/todo</code> directly to examine it or write a one-off patch. See <a class="link" href="#detached-head" title="Examining an old version without creating a new branch">detached head</a>.</p> <p>Note that the name "origin" is just the name that Git uses by default to refer to the repository that you cloned from.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="how-git-stores-references"></a>Naming branches, tags, and other references</h2></div></div></div> <p>Branches, remote-tracking branches, and tags are all references to commits. All references are named with a slash-separated path name starting with <code class="literal">refs</code>; the names we’ve been using so far are actually shorthand:</p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> The branch <code class="literal">test</code> is short for <code class="literal">refs/heads/test</code>. </li><li class="listitem"> The tag <code class="literal">v2.6.18</code> is short for <code class="literal">refs/tags/v2.6.18</code>. </li><li class="listitem"> <code class="literal">origin/master</code> is short for <code class="literal">refs/remotes/origin/master</code>. </li></ul></div> <p>The full name is occasionally useful if, for example, there ever exists a tag and a branch with the same name.</p> <p>(Newly created refs are actually stored in the <code class="literal">.git/refs</code> directory, under the path given by their name. However, for efficiency reasons they may also be packed together in a single file; see <a class="ulink" href="git-pack-refs.html" target="_top">git-pack-refs(1)</a>).</p> <p>As another useful shortcut, the "HEAD" of a repository can be referred to just using the name of that repository. So, for example, "origin" is usually a shortcut for the HEAD branch in the repository "origin".</p> <p>For the complete list of paths which Git checks for references, and the order it uses to decide which to choose when there are multiple references with the same shorthand name, see the "SPECIFYING REVISIONS" section of <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a>.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="Updating-a-repository-With-git-fetch"></a>Updating a repository with git fetch</h2></div></div></div> <p>After you clone a repository and commit a few changes of your own, you may wish to check the original repository for updates.</p> <p>The <code class="literal">git-fetch</code> command, with no arguments, will update all of the remote-tracking branches to the latest version found in the original repository. It will not touch any of your own branches—not even the "master" branch that was created for you on clone.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="fetching-branches"></a>Fetching branches from other repositories</h2></div></div></div> <p>You can also track branches from repositories other than the one you cloned from, using <a class="ulink" href="git-remote.html" target="_top">git-remote(1)</a>:</p> <pre class="screen">$ git remote add staging git://git.kernel.org/.../gregkh/staging.git $ git fetch staging ... From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging * [new branch] master -> staging/master * [new branch] staging-linus -> staging/staging-linus * [new branch] staging-next -> staging/staging-next</pre> <p>New remote-tracking branches will be stored under the shorthand name that you gave <code class="literal">git remote add</code>, in this case <code class="literal">staging</code>:</p> <pre class="screen">$ git branch -r origin/HEAD -> origin/master origin/master staging/master staging/staging-linus staging/staging-next</pre> <p>If you run <code class="literal">git fetch <remote></code> later, the remote-tracking branches for the named <code class="literal"><remote></code> will be updated.</p> <p>If you examine the file <code class="literal">.git/config</code>, you will see that Git has added a new stanza:</p> <pre class="screen">$ cat .git/config ... [remote "staging"] url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git fetch = +refs/heads/*:refs/remotes/staging/* ...</pre> <p>This is what causes Git to track the remote’s branches; you may modify or delete these configuration options by editing <code class="literal">.git/config</code> with a text editor. (See the "CONFIGURATION FILE" section of <a class="ulink" href="git-config.html" target="_top">git-config(1)</a> for details.)</p> </div> </div> <div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="exploring-git-history"></a>Chapter 2. Exploring Git history</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#using-bisect">How to use bisect to find a regression</a></span></dt><dt><span class="section"><a href="#naming-commits">Naming commits</a></span></dt><dt><span class="section"><a href="#creating-tags">Creating tags</a></span></dt><dt><span class="section"><a href="#browsing-revisions">Browsing revisions</a></span></dt><dt><span class="section"><a href="#generating-diffs">Generating diffs</a></span></dt><dt><span class="section"><a href="#viewing-old-file-versions">Viewing old file versions</a></span></dt><dt><span class="section"><a href="#history-examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="#counting-commits-on-a-branch">Counting the number of commits on a branch</a></span></dt><dt><span class="section"><a href="#checking-for-equal-branches">Check whether two branches point at the same history</a></span></dt><dt><span class="section"><a href="#finding-tagged-descendants">Find first tagged version including a given fix</a></span></dt><dt><span class="section"><a href="#showing-commits-unique-to-a-branch">Showing commits unique to a given branch</a></span></dt><dt><span class="section"><a href="#making-a-release">Creating a changelog and tarball for a software release</a></span></dt><dt><span class="section"><a href="#Finding-commits-With-given-Content">Finding commits referencing a file with given content</a></span></dt></dl></dd></dl></div> <p>Git is best thought of as a tool for storing the history of a collection of files. It does this by storing compressed snapshots of the contents of a file hierarchy, together with "commits" which show the relationships between these snapshots.</p> <p>Git provides extremely flexible and fast tools for exploring the history of a project.</p> <p>We start with one specialized tool that is useful for finding the commit that introduced a bug into a project.</p> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="using-bisect"></a>How to use bisect to find a regression</h2></div></div></div> <p>Suppose version 2.6.18 of your project worked, but the version at "master" crashes. Sometimes the best way to find the cause of such a regression is to perform a brute-force search through the project’s history to find the particular commit that caused the problem. The <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> command can help you do this:</p> <pre class="screen">$ git bisect start $ git bisect good v2.6.18 $ git bisect bad master Bisecting: 3537 revisions left to test after this [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]</pre> <p>If you run <code class="literal">git branch</code> at this point, you’ll see that Git has temporarily moved you in "(no branch)". HEAD is now detached from any branch and points directly to a commit (with commit id 65934) that is reachable from "master" but not from v2.6.18. Compile and test it, and see whether it crashes. Assume it does crash. Then:</p> <pre class="screen">$ git bisect bad Bisecting: 1769 revisions left to test after this [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings</pre> <p>checks out an older version. Continue like this, telling Git at each stage whether the version it gives you is good or bad, and notice that the number of revisions left to test is cut approximately in half each time.</p> <p>After about 13 tests (in this case), it will output the commit id of the guilty commit. You can then examine the commit with <a class="ulink" href="git-show.html" target="_top">git-show(1)</a>, find out who wrote it, and mail them your bug report with the commit id. Finally, run</p> <pre class="screen">$ git bisect reset</pre> <p>to return you to the branch you were on before.</p> <p>Note that the version which <code class="literal">git bisect</code> checks out for you at each point is just a suggestion, and you’re free to try a different version if you think it would be a good idea. For example, occasionally you may land on a commit that broke something unrelated; run</p> <pre class="screen">$ git bisect visualize</pre> <p>which will run gitk and label the commit it chose with a marker that says "bisect". Choose a safe-looking commit nearby, note its commit id, and check it out with:</p> <pre class="screen">$ git reset --hard fb47ddb2db</pre> <p>then test, run <code class="literal">bisect good</code> or <code class="literal">bisect bad</code> as appropriate, and continue.</p> <p>Instead of <code class="literal">git bisect visualize</code> and then <code class="literal">git reset --hard fb47ddb2db</code>, you might just want to tell Git that you want to skip the current commit:</p> <pre class="screen">$ git bisect skip</pre> <p>In this case, though, Git may not eventually be able to tell the first bad one between some first skipped commits and a later bad commit.</p> <p>There are also ways to automate the bisecting process if you have a test script that can tell a good from a bad commit. See <a class="ulink" href="git-bisect.html" target="_top">git-bisect(1)</a> for more information about this and other <code class="literal">git bisect</code> features.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="naming-commits"></a>Naming commits</h2></div></div></div> <p>We have seen several ways of naming commits already:</p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 40-hexdigit object name </li><li class="listitem"> branch name: refers to the commit at the head of the given branch </li><li class="listitem"> tag name: refers to the commit pointed to by the given tag (we’ve seen branches and tags are special cases of <a class="link" href="#how-git-stores-references" title="Naming branches, tags, and other references">references</a>). </li><li class="listitem"> HEAD: refers to the head of the current branch </li></ul></div> <p>There are many more; see the "SPECIFYING REVISIONS" section of the <a class="ulink" href="gitrevisions.html" target="_top">gitrevisions(7)</a> man page for the complete list of ways to name revisions. Some examples:</p> <pre class="screen">$ git show fb47ddb2 # the first few characters of the object name # are usually enough to specify it uniquely $ git show HEAD^ # the parent of the HEAD commit $ git show HEAD^^ # the grandparent $ git show HEAD~4 # the great-great-grandparent</pre> <p>Recall that merge commits may have more than one parent; by default, <code class="literal">^</code> and <code class="literal">~</code> follow the first parent listed in the commit, but you can also choose:</p> <pre class="screen">$ git show HEAD^1 # show the first parent of HEAD $ git show HEAD^2 # show the second parent of HEAD</pre> <p>In addition to HEAD, there are several other special names for commits:</p> <p>Merges (to be discussed later), as well as operations such as <code class="literal">git reset</code>, which change the currently checked-out commit, generally set ORIG_HEAD to the value HEAD had before the current operation.</p> <p>The <code class="literal">git fetch</code> operation always stores the head of the last fetched branch in FETCH_HEAD. For example, if you run <code class="literal">git fetch</code> without specifying a local branch as the target of the operation</p> <pre class="screen">$ git fetch git://example.com/proj.git theirbranch</pre> <p>the fetched commits will still be available from FETCH_HEAD.</p> <p>When we discuss merges we’ll also see the special name MERGE_HEAD, which refers to the other branch that we’re merging in to the current branch.</p> <p>The <a class="ulink" href="git-rev-parse.html" target="_top">git-rev-parse(1)</a> command is a low-level command that is occasionally useful for translating some name for a commit to the object name for that commit:</p> <pre class="screen">$ git rev-parse origin e05db0fd4f31dde7005f075a84f96b360d05984b</pre> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="creating-tags"></a>Creating tags</h2></div></div></div> <p>We can also create a tag to refer to a particular commit; after running</p> <pre class="screen">$ git tag stable-1 1b2e1d63ff</pre> <p>You can use <code class="literal">stable-1</code> to refer to the commit 1b2e1d63ff.</p> <p>This creates a "lightweight" tag. If you would also like to include a comment with the tag, and possibly sign it cryptographically, then you should create a tag object instead; see the <a class="ulink" href="git-tag.html" target="_top">git-tag(1)</a> man page for details.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="browsing-revisions"></a>Browsing revisions</h2></div></div></div> <p>The <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> command can show lists of commits. On its own, it shows all commits reachable from the parent commit; but you can also make more specific requests:</p> <pre class="screen">$ git log v2.5.. # commits since (not reachable from) v2.5 $ git log test..master # commits reachable from master but not test $ git log master..test # ...reachable from test but not master $ git log master...test # ...reachable from either test or master, # but not both $ git log --since="2 weeks ago" # commits from the last 2 weeks $ git log Makefile # commits which modify Makefile $ git log fs/ # ... which modify any file under fs/ $ git log -S'foo()' # commits which add or remove any file data # matching the string 'foo()'</pre> <p>And of course you can combine all of these; the following finds commits since v2.5 which touch the <code class="literal">Makefile</code> or any file under <code class="literal">fs</code>:</p> <pre class="screen">$ git log v2.5.. Makefile fs/</pre> <p>You can also ask git log to show patches:</p> <pre class="screen">$ git log -p</pre> <p>See the <code class="literal">--pretty</code> option in the <a class="ulink" href="git-log.html" target="_top">git-log(1)</a> man page for more display options.</p> <p>Note that git log starts with the most recent commit and works backwards through the parents; however, since Git history can contain multiple independent lines of development, the particular order that commits are listed in may be somewhat arbitrary.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generating-diffs"></a>Generating diffs</h2></div></div></div> <p>You can generate diffs between any two versions using <a class="ulink" href="git-diff.html" target="_top">git-diff(1)</a>:</p> <pre class="screen">$ git diff master..test</pre> <p>That will produce the diff between the tips of the two branches. If you’d prefer to find the diff from their common ancestor to test, you can use three dots instead of two:</p> <pre class="screen">$ git diff master...test</pre> <p>Sometimes what you want instead is a set of patches; for this you can use <a class="ulink" href="git-format-patch.html" target="_top">git-format-patch(1)</a>:</p> <pre class="screen">$ git format-patch master..test</pre> <p>will generate a file with a patch for each commit reachable from test but not from master.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="viewing-old-file-versions"></a>Viewing old file versions</h2></div></div></div> <p>You can always view an old version of a file by just checking out the correct revision first. But sometimes it is more convenient to be able to view an old version of a single file without checking anything out; this command does that:</p> <pre class="screen">$ git show v2.5:fs/locks.c</pre> <p>Before the colon may be anything that names a commit, and after it may be any path to a file tracked by Git.</p> </div> <div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="history-examples"></a>Examples</h2></div></div></div> <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="counting-commits-on-a-branch"></a>Counting the number of commits on a branch</h3></div></div></div> <p>Suppose you want to know how many commits you’ve made on <code class="literal">mybranch</code> since it diverged from <code class="literal">origin</code>:</p> <pre class="screen">$ git log --pretty=oneline origin..mybranch | wc -l</pre> <p>Alternatively, you may often see this sort of thing done with the lower-level command <a class="ulink" href="git-rev-list.html" target="_top">git-rev-list(1)</a>, which just lists the SHA-1’s of all the given commits:</p> <pre class="screen">$ git rev-list origin..mybranch | wc -l</pre> </div> <div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="checking-for-equal-branches"></a>Check whether two branches point at the same history</h3></div></div></div> <p>Suppose you want to check whether two branches point at the same point in history.</p> <pre class="screen">$ git diff origin..master</pre> <p>will tell you whether the contents of the project are the same at the two branches; in theory, however, it’s possible that the same project contents could have been arrived at by two different historical routes. You could compare the object names:</p> <pre class="screen">$ git rev-list origin e05db0fd4f31dde7005f075a84f96b360d05984b $ git rev-list master e05db0fd4f31dde7005f075a84f96b360d05984b</pre> <p>Or you could recall that the <code class="literal">...</code> operator selects all commits reachable from either one reference or the other but not both; so</p> <pre class="screen">$ git log origin...master</pre> <p>will return no commits when the two branches are equal.</p> </div> <div class="section"><div c