= Git User Manual Git is a fast distributed revision control system. This manual is designed to be readable by someone with basic UNIX command-line skills, but no previous knowledge of Git. <> and <> 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. People needing to do actual development will also want to read <> and <>. Further chapters cover more specialized topics. Comprehensive reference documentation is available through the man pages, or linkgit:git-help[1] command. For example, for the command `git clone `, you can either use: ------------------------------------------------ $ man git-clone ------------------------------------------------ or: ------------------------------------------------ $ git help clone ------------------------------------------------ With the latter, you can use the manual viewer of your choice; see linkgit:git-help[1] for more information. See also <> for a brief overview of Git commands, without any explanation. Finally, see <> for ways that you can help make this manual more complete. [[repositories-and-branches]] == Repositories and Branches [[how-to-get-a-git-repository]] === How to get a Git repository It will be useful to have a Git repository to experiment with as you read this manual. The best way to get one is by using the linkgit:git-clone[1] command to download a copy of an existing repository. If you don't already have a project in mind, here are some interesting examples: ------------------------------------------------ # 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 ------------------------------------------------ The initial clone may be time-consuming for a large project, but you will only need to clone once. The clone command creates a new directory named after the project (`git` or `linux` in the examples above). After you cd into this directory, you will see that it contains a copy of the project files, called the <>, together with a special top-level directory named `.git`, which contains all the information about the history of the project. [[how-to-check-out]] === How to check out a different version of a project 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 <>. 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 <>, which may merge and diverge. A single Git repository can track development on multiple branches. It does this by keeping a list of <> which reference the latest commit on each branch; the linkgit:git-branch[1] command shows you the list of branch heads: ------------------------------------------------ $ git branch * master ------------------------------------------------ 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. Most projects also use <>. Tags, like heads, are references into the project's history, and can be listed using the linkgit:git-tag[1] command: ------------------------------------------------ $ 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 ... ------------------------------------------------ Tags are expected to always point at the same version of a project, while heads are expected to advance as development progresses. Create a new branch head pointing to one of these versions and check it out using linkgit:git-switch[1]: ------------------------------------------------ $ git switch -c new v2.6.13 ------------------------------------------------ The working directory then reflects the contents that the project had when it was tagged v2.6.13, and linkgit:git-branch[1] shows two branches, with an asterisk marking the currently checked-out branch: ------------------------------------------------ $ git branch master * new ------------------------------------------------ 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 ------------------------------------------------ $ git reset --hard v2.6.17 ------------------------------------------------ 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. [[understanding-commits]] === Understanding History: Commits Every change in the history of a project is represented by a commit. The linkgit:git-show[1] command shows the most recent commit on the current branch: ------------------------------------------------ $ git show commit 17cf781661e6d38f737f15f53ab552f1e95960d7 Author: Linus Torvalds 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) { ------------------------------------------------ As you can see, a commit shows who made the latest change, what they did, and why. Every commit has a 40-hexdigit id, sometimes called the "object name" or the "SHA-1 id", shown on the first line of the `git show` 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. In fact, in <> 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. [[understanding-reachability]] ==== Understanding history: commits, parents, and reachability 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. 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. The best way to see how this works is using the linkgit:gitk[1] command; running gitk now on a Git repository and looking for merge commits will help understand how Git organizes history. 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. [[history-diagrams]] ==== Understanding history: History diagrams 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: ................................................ o--o--o <-- Branch A / o--o--o <-- master \ o--o--o <-- Branch B ................................................ If we need to talk about a particular commit, the character "o" may be replaced with another letter or number. [[what-is-a-branch]] ==== Understanding history: What is a branch? 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". However, when no confusion will result, we often just use the term "branch" both for branches and for branch heads. [[manipulating-branches]] === Manipulating branches Creating, deleting, and modifying branches is quick and easy; here's a summary of the commands: `git branch`:: list all branches. `git branch `:: create a new branch named ``, referencing the same point in history as the current branch. `git branch `:: create a new branch named ``, referencing ``, which may be specified any way you like, including using a branch name or a tag name. `git branch -d `:: delete the branch ``; if the branch is not fully merged in its upstream branch or contained in the current branch, this command will fail with a warning. `git branch -D `:: delete the branch `` irrespective of its merged status. `git switch `:: make the current branch ``, updating the working directory to reflect the version referenced by ``. `git switch -c `:: create a new branch `` referencing ``, and check it out. The special symbol "HEAD" can always be used to refer to the current branch. In fact, Git uses a file named `HEAD` in the `.git` directory to remember which branch is current: ------------------------------------------------ $ cat .git/HEAD ref: refs/heads/master ------------------------------------------------ [[detached-head]] === Examining an old version without creating a new branch The `git switch` 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: ------------------------------------------------ $ 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 ------------------------------------------------ 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: ------------------------------------------------ $ cat .git/HEAD 427abfa28afedffadfca9dd8b067eb6d36bac53f $ git branch * (detached from v2.6.17) master ------------------------------------------------ In this case we say that the HEAD is "detached". 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. [[examining-remote-branches]] === Examining branches from a remote repository 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 `-r` option to linkgit:git-branch[1]: ------------------------------------------------ $ git branch -r origin/HEAD origin/html origin/maint origin/man origin/master origin/next origin/seen origin/todo ------------------------------------------------ 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 `git fetch` (hence `git pull`) and `git push`. See <> for details. 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: ------------------------------------------------ $ git switch -c my-todo-copy origin/todo ------------------------------------------------ You can also check out `origin/todo` directly to examine it or write a one-off patch. See <>. Note that the name "origin" is just the name that Git uses by default to refer to the repository that you cloned from. [[how-git-stores-references]] === Naming branches, tags, and other references Branches, remote-tracking branches, and tags are all references to commits. All references are named with a slash-separated path name starting with `refs`; the names we've been using so far are actually shorthand: - The branch `test` is short for `refs/heads/test`. - The tag `v2.6.18` is short for `refs/tags/v2.6.18`. - `origin/master` is short for `refs/remotes/origin/master`. The full name is occasionally useful if, for example, there ever exists a tag and a branch with the same name. (Newly created refs are actually stored in the `.git/refs` directory, under the path given by their name. However, for efficiency reasons they may also be packed together in a single file; see linkgit:git-pack-refs[1]). 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". 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 linkgit:gitrevisions[7]. [[Updating-a-repository-With-git-fetch]] === Updating a repository with git fetch After you clone a repository and commit a few changes of your own, you may wish to check the original repository for updates. The `git-fetch` 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. [[fetching-branches]] === Fetching branches from other repositories You can also track branches from repositories other than the one you cloned from, using linkgit:git-remote[1]: ------------------------------------------------- $ 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 ------------------------------------------------- New remote-tracking branches will be stored under the shorthand name that you gave `git remote add`, in this case `staging`: ------------------------------------------------- $ git branch -r origin/HEAD -> origin/master origin/master staging/master staging/staging-linus staging/staging-next ------------------------------------------------- If you run `git fetch ` later, the remote-tracking branches for the named `` will be updated. If you examine the file `.git/config`, you will see that Git has added a new stanza: ------------------------------------------------- $ cat .git/config ... [remote "staging"] url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git fetch = +refs/heads/*:refs/remotes/staging/* ... ------------------------------------------------- This is what causes Git to track the remote's branches; you may modify or delete these configuration options by editing `.git/config` with a text editor. (See the "CONFIGURATION FILE" section of linkgit:git-config[1] for details.) [[exploring-git-history]] == Exploring Git history 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. Git provides extremely flexible and fast tools for exploring the history of a project. We start with one specialized tool that is useful for finding the commit that introduced a bug into a project. [[using-bisect]] === How to use bisect to find a regression 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 linkgit:git-bisect[1] command can help you do this: ------------------------------------------------- $ 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] ------------------------------------------------- If you run `git branch` 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: ------------------------------------------------- $ git bisect bad Bisecting: 1769 revisions left to test after this [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings ------------------------------------------------- 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. After about 13 tests (in this case), it will output the commit id of the guilty commit. You can then examine the commit with linkgit:git-show[1], find out who wrote it, and mail them your bug report with the commit id. Finally, run ------------------------------------------------- $ git bisect reset ------------------------------------------------- to return you to the branch you were on before. Note that the version which `git bisect` 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 ------------------------------------------------- $ git bisect visualize ------------------------------------------------- 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: ------------------------------------------------- $ git reset --hard fb47ddb2db ------------------------------------------------- then test, run `bisect good` or `bisect bad` as appropriate, and continue. Instead of `git bisect visualize` and then `git reset --hard fb47ddb2db`, you might just want to tell Git that you want to skip the current commit: ------------------------------------------------- $ git bisect skip ------------------------------------------------- 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. 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 linkgit:git-bisect[1] for more information about this and other `git bisect` features. [[naming-commits]] === Naming commits We have seen several ways of naming commits already: - 40-hexdigit object name - branch name: refers to the commit at the head of the given branch - tag name: refers to the commit pointed to by the given tag (we've seen branches and tags are special cases of <>). - HEAD: refers to the head of the current branch There are many more; see the "SPECIFYING REVISIONS" section of the linkgit:gitrevisions[7] man page for the complete list of ways to name revisions. Some examples: ------------------------------------------------- $ 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 ------------------------------------------------- Recall that merge commits may have more than one parent; by default, `^` and `~` follow the first parent listed in the commit, but you can also choose: ------------------------------------------------- $ git show HEAD^1 # show the first parent of HEAD $ git show HEAD^2 # show the second parent of HEAD ------------------------------------------------- In addition to HEAD, there are several other special names for commits: Merges (to be discussed later), as well as operations such as `git reset`, which change the currently checked-out commit, generally set ORIG_HEAD to the value HEAD had before the current operation. The `git fetch` operation always stores the head of the last fetched branch in FETCH_HEAD. For example, if you run `git fetch` without specifying a local branch as the target of the operation ------------------------------------------------- $ git fetch git://example.com/proj.git theirbranch ------------------------------------------------- the fetched commits will still be available from FETCH_HEAD. 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. The linkgit:git-rev-parse[1] command is a low-level command that is occasionally useful for translating some name for a commit to the object name for that commit: ------------------------------------------------- $ git rev-parse origin e05db0fd4f31dde7005f075a84f96b360d05984b ------------------------------------------------- [[creating-tags]] === Creating tags We can also create a tag to refer to a particular commit; after running ------------------------------------------------- $ git tag stable-1 1b2e1d63ff ------------------------------------------------- You can use `stable-1` to refer to the commit 1b2e1d63ff. 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 linkgit:git-tag[1] man page for details. [[browsing-revisions]] === Browsing revisions The linkgit:git-log[1] 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: ------------------------------------------------- $ 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()' ------------------------------------------------- And of course you can combine all of these; the following finds commits since v2.5 which touch the `Makefile` or any file under `fs`: ------------------------------------------------- $ git log v2.5.. Makefile fs/ ------------------------------------------------- You can also ask git log to show patches: ------------------------------------------------- $ git log -p ------------------------------------------------- See the `--pretty` option in the linkgit:git-log[1] man page for more display options. 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. [[generating-diffs]] === Generating diffs You can generate diffs between any two versions using linkgit:git-diff[1]: ------------------------------------------------- $ git diff master..test ------------------------------------------------- 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: ------------------------------------------------- $ git diff master...test ------------------------------------------------- Sometimes what you want instead is a set of patches; for this you can use linkgit:git-format-patch[1]: ------------------------------------------------- $ git format-patch master..test ------------------------------------------------- will generate a file with a patch for each commit reachable from test but not from master. [[viewing-old-file-versions]] === Viewing old file versions 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: ------------------------------------------------- $ git show v2.5:fs/locks.c ------------------------------------------------- Before the colon may be anything that names a commit, and after it may be any path to a file tracked by Git. [[history-examples]] === Examples [[counting-commits-on-a-branch]] ==== Counting the number of commits on a branch Suppose you want to know how many commits you've made on `mybranch` since it diverged from `origin`: ------------------------------------------------- $ git log --pretty=oneline origin..mybranch | wc -l ------------------------------------------------- Alternatively, you may often see this sort of thing done with the lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's of all the given commits: ------------------------------------------------- $ git rev-list origin..mybranch | wc -l ------------------------------------------------- [[checking-for-equal-branches]] ==== Check whether two branches point at the same history Suppose you want to check whether two branches point at the same point in history. ------------------------------------------------- $ git diff origin..master ------------------------------------------------- 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: ------------------------------------------------- $ git rev-list origin e05db0fd4f31dde7005f075a84f96b360d05984b $ git rev-list master e05db0fd4f31dde7005f075a84f96b360d05984b ------------------------------------------------- Or you could recall that the `...` operator selects all commits reachable from either one reference or the other but not both; so ------------------------------------------------- $ git log origin...master ------------------------------------------------- will return no commits when the two branches are equal. [[finding-tagged-descendants]] ==== Find first tagged version including a given fix Suppose you know that the commit e05db0fd fixed a certain problem. You'd like to find the earliest tagged release that contains that fix. Of course, there may be more than one answer--if the history branched after commit e05db0fd, then there could be multiple "earliest" tagged releases. You could just visually inspect the commits since e05db0fd: ------------------------------------------------- $ gitk e05db0fd.. ------------------------------------------------- or you can use linkgit:git-name-rev[1], which will give the commit a name based on any tag it finds pointing to one of the commit's descendants: ------------------------------------------------- $ git name-rev --tags e05db0fd e05db0fd tags/v1.5.0-rc1^0~23 ------------------------------------------------- The linkgit:git-describe[1] command does the opposite, naming the revision using a tag on which the given commit is based: ------------------------------------------------- $ git describe e05db0fd v1.5.0-rc0-260-ge05db0f ------------------------------------------------- but that may sometimes help you guess which tags might come after the given commit. If you just want to verify whether a given tagged version contains a given commit, you could use linkgit:git-merge-base[1]: ------------------------------------------------- $ git merge-base e05db0fd v1.5.0-rc1 e05db0fd4f31dde7005f075a84f96b360d05984b ------------------------------------------------- The merge-base command finds a common ancestor of the given commits, and always returns one or the other in the case where one is a descendant of the other; so the above output shows that e05db0fd actually is an ancestor of v1.5.0-rc1. Alternatively, note that ------------------------------------------------- $ git log v1.5.0-rc1..e05db0fd ------------------------------------------------- will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, because it outputs only commits that are not reachable from v1.5.0-rc1. As yet another alternative, the linkgit:git-show-branch[1] command lists the commits reachable from its arguments with a display on the left-hand side that indicates which arguments that commit is reachable from. So, if you run something like ------------------------------------------------- $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if available ! [v1.5.0-rc0] GIT v1.5.0 preview ! [v1.5.0-rc1] GIT v1.5.0-rc1 ! [v1.5.0-rc2] GIT v1.5.0-rc2 ... ------------------------------------------------- then a line like ------------------------------------------------- + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if available ------------------------------------------------- shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and from v1.5.0-rc2, and not from v1.5.0-rc0. [[showing-commits-unique-to-a-branch]] ==== Showing commits unique to a given branch Suppose you would like to see all the commits reachable from the branch head named `master` but not from any other head in your repository. We can list all the heads in this repository with linkgit:git-show-ref[1]: ------------------------------------------------- $ git show-ref --heads bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes ------------------------------------------------- We can get just the branch-head names, and remove `master`, with the help of the standard utilities cut and grep: ------------------------------------------------- $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' refs/heads/core-tutorial refs/heads/maint refs/heads/tutorial-2 refs/heads/tutorial-fixes ------------------------------------------------- And then we can ask to see all the commits reachable from master but not from these other heads: ------------------------------------------------- $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' ) ------------------------------------------------- Obviously, endless variations are possible; for example, to see all commits reachable from some head but not from any tag in the repository: ------------------------------------------------- $ gitk $( git show-ref --heads ) --not $( git show-ref --tags ) ------------------------------------------------- (See linkgit:gitrevisions[7] for explanations of commit-selecting syntax such as `--not`.) [[making-a-release]] ==== Creating a changelog and tarball for a software release The linkgit:git-archive[1] command can create a tar or zip archive from any version of a project; for example: ------------------------------------------------- $ git archive -o latest.tar.gz --prefix=project/ HEAD ------------------------------------------------- will use HEAD to produce a gzipped tar archive in which each filename is preceded by `project/`. The output file format is inferred from the output file extension if possible, see linkgit:git-archive[1] for details. Versions of Git older than 1.7.7 don't know about the `tar.gz` format, you'll need to use gzip explicitly: ------------------------------------------------- $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz ------------------------------------------------- If you're releasing a new version of a software project, you may want to simultaneously make a changelog to include in the release announcement. Linus Torvalds, for example, makes new kernel releases by tagging them, then running: ------------------------------------------------- $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7 ------------------------------------------------- where release-script is a shell script that looks like: ------------------------------------------------- #!/bin/sh stable="$1" last="$2" new="$3" echo "# git tag v$new" echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz" echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz" echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new" echo "git shortlog --no-merges v$new ^v$last > ../ShortLog" echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new" ------------------------------------------------- and then he just cut-and-pastes the output commands after verifying that they look OK. [[Finding-commits-With-given-Content]] ==== Finding commits referencing a file with given content Somebody hands you a copy of a file, and asks which commits modified a file such that it contained the given content either before or after the commit. You can find out with this: ------------------------------------------------- $ git log --raw --abbrev=40 --pretty=oneline | grep -B 1 `git hash-object filename` ------------------------------------------------- Figuring out why this works is left as an exercise to the (advanced) student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and linkgit:git-hash-object[1] man pages may prove helpful. [[Developing-With-git]] == Developing with Git [[telling-git-your-name]] === Telling Git your name Before creating any commits, you should introduce yourself to Git. The easiest way to do so is to use linkgit:git-config[1]: ------------------------------------------------ $ git config --global user.name 'Your Name Comes Here' $ git config --global user.email 'you@yourdomain.example.com' ------------------------------------------------ Which will add the following to a file named `.gitconfig` in your home directory: ------------------------------------------------ [user] name = Your Name Comes Here email = you@yourdomain.example.com ------------------------------------------------ See the "CONFIGURATION FILE" section of linkgit:git-config[1] for details on the configuration file. The file is plain text, so you can also edit it with your favorite editor. [[creating-a-new-repository]] === Creating a new repository Creating a new repository from scratch is very easy: ------------------------------------------------- $ mkdir project $ cd project $ git init ------------------------------------------------- If you have some initial content (say, a tarball): ------------------------------------------------- $ tar xzvf project.tar.gz $ cd project $ git init $ git add . # include everything below ./ in the first commit: $ git commit ------------------------------------------------- [[how-to-make-a-commit]] === How to make a commit Creating a new commit takes three steps: 1. Making some changes to the working directory using your favorite editor. 2. Telling Git about your changes. 3. Creating the commit using the content you told Git about in step 2. In practice, you can interleave and repeat steps 1 and 2 as many times as you want: in order to keep track of what you want committed at step 3, Git maintains a snapshot of the tree's contents in a special staging area called "the index." At the beginning, the content of the index will be identical to that of the HEAD. The command `git diff --cached`, which shows the difference between the HEAD and the index, should therefore produce no output at that point. Modifying the index is easy: To update the index with the contents of a new or modified file, use ------------------------------------------------- $ git add path/to/file ------------------------------------------------- To remove a file from the index and from the working tree, use ------------------------------------------------- $ git rm path/to/file ------------------------------------------------- After each step you can verify that ------------------------------------------------- $ git diff --cached ------------------------------------------------- always shows the difference between the HEAD and the index file--this is what you'd commit if you created the commit now--and that ------------------------------------------------- $ git diff ------------------------------------------------- shows the difference between the working tree and the index file. Note that `git add` always adds just the current contents of a file to the index; further changes to the same file will be ignored unless you run `git add` on the file again. When you're ready, just run ------------------------------------------------- $ git commit ------------------------------------------------- and Git will prompt you for a commit message and then create the new commit. Check to make sure it looks like what you expected with ------------------------------------------------- $ git show ------------------------------------------------- As a special shortcut, ------------------------------------------------- $ git commit -a ------------------------------------------------- will update the index with any files that you've modified or removed and create a commit, all in one step. A number of commands are useful for keeping track of what you're about to commit: ------------------------------------------------- $ git diff --cached # difference between HEAD and the index; what # would be committed if you ran "commit" now. $ git diff # difference between the index file and your # working directory; changes that would not # be included if you ran "commit" now. $ git diff HEAD # difference between HEAD and working tree; what # would be committed if you ran "commit -a" now. $ git status # a brief per-file summary of the above. ------------------------------------------------- You can also use linkgit:git-gui[1] to create commits, view changes in the index and the working tree files, and individually select diff hunks for inclusion in the index (by right-clicking on the diff hunk and choosing "Stage Hunk For Commit"). [[creating-good-commit-messages]] === Creating good commit messages Though not required, it's a good idea to begin the commit message with a single short (less than 50 character) line summarizing the change, followed by a blank line and then a more thorough description. The text up to the first blank line in a commit message is treated as the commit title, and that title is used throughout Git. For example, linkgit:git-format-patch[1] turns a commit into email, and it uses the title on the Subject line and the rest of the commit in the body. [[ignoring-files]] === Ignoring files A project will often generate files that you do 'not' want to track with Git. This typically includes files generated by a build process or temporary backup files made by your editor. Of course, 'not' tracking files with Git is just a matter of 'not' calling `git add` on them. But it quickly becomes annoying to have these untracked files lying around; e.g. they make `git add .` practically useless, and they keep showing up in the output of `git status`. You can tell Git to ignore certain files by creating a file called `.gitignore` in the top level of your working directory, with contents such as: ------------------------------------------------- # Lines starting with '#' are considered comments. # Ignore any file named foo.txt. foo.txt # Ignore (generated) html files, *.html # except foo.html which is maintained by hand. !foo.html # Ignore objects and archives. *.[oa] ------------------------------------------------- See linkgit:gitignore[5] for a detailed explanation of the syntax. You can also place .gitignore files in other directories in your working tree, and they will apply to those directories and their subdirectories. The `.gitignore` files can be added to your repository like any other files (just run `git add .gitignore` and `git commit`, as usual), which is convenient when the exclude patterns (such as patterns matching build output files) would also make sense for other users who clone your repository. If you wish the exclude patterns to affect only certain repositories (instead of every repository for a given project), you may instead put them in a file in your repository named `.git/info/exclude`, or in any file specified by the `core.excludesFile` configuration variable. Some Git commands can also take exclude patterns directly on the command line. See linkgit:gitignore[5] for the details. [[how-to-merge]] === How to merge You can rejoin two diverging branches of development using linkgit:git-merge[1]: ------------------------------------------------- $ git merge branchname ------------------------------------------------- merges the development in the branch `branchname` into the current branch. A merge is made by combining the changes made in `branchname` and the changes made up to the latest commit in your current branch since their histories forked. The work tree is overwritten by the result of the merge when this combining is done cleanly, or overwritten by a half-merged results when this combining results in conflicts. Therefore, if you have uncommitted changes touching the same files as the ones impacted by the merge, Git will refuse to proceed. Most of the time, you will want to commit your changes before you can merge, and if you don't, then linkgit:git-stash[1] can take these changes away while you're doing the merge, and reapply them afterwards. If the changes are independent enough, Git will automatically complete the merge and commit the result (or reuse an existing commit in case of <>, see below). On the other hand, if there are conflicts--for example, if the same file is modified in two different ways in the remote branch and the local branch--then you are warned; the output may look something like this: ------------------------------------------------- $ git merge next 100% (4/4) done Auto-merged file.txt CONFLICT (content): Merge conflict in file.txt Automatic merge failed; fix conflicts and then commit the result. ------------------------------------------------- Conflict markers are left in the problematic files, and after you resolve the conflicts manually, you can update the index with the contents and run Git commit, as you normally would when creating a new file. If you examine the resulting commit using gitk, you will see that it has two parents, one pointing to the top of the current branch, and one to the top of the other branch. [[resolving-a-merge]] === Resolving a merge When a merge isn't resolved automatically, Git leaves the index and the working tree in a special state that gives you all the information you need to help resolve the merge. Files with conflicts are marked specially in the index, so until you resolve the problem and update the index, linkgit:git-commit[1] will fail: ------------------------------------------------- $ git commit file.txt: needs merge ------------------------------------------------- Also, linkgit:git-status[1] will list those files as "unmerged", and the files with conflicts will have conflict markers added, like this: ------------------------------------------------- <<<<<<< HEAD:file.txt Hello world ======= Goodbye >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt ------------------------------------------------- All you need to do is edit the files to resolve the conflicts, and then ------------------------------------------------- $ git add file.txt $ git commit ------------------------------------------------- Note that the commit message will already be filled in for you with some information about the merge. Normally you can just use this default message unchanged, but you may add additional commentary of your own if desired. The above is all you need to know to resolve a simple merge. But Git also provides more information to help resolve conflicts: [[conflict-resolution]] ==== Getting conflict-resolution help during a merge All of the changes that Git was able to merge automatically are already added to the index file, so linkgit:git-diff[1] shows only the conflicts. It uses an unusual syntax: ------------------------------------------------- $ git diff diff --cc file.txt index 802992c,2b60207..0000000 --- a/file.txt +++ b/file.txt @@@ -1,1 -1,1 +1,5 @@@ ++<<<<<<< HEAD:file.txt +Hello world ++======= + Goodbye ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt ------------------------------------------------- Recall that the commit which will be committed after we resolve this conflict will have two parents instead of the usual one: one parent will be HEAD, the tip of the current branch; the other will be the tip of the other branch, which is stored temporarily in MERGE_HEAD. During the merge, the index holds three versions of each file. Each of these three "file stages" represents a different version of the file: ------------------------------------------------- $ git show :1:file.txt # the file in a common ancestor of both branches $ git show :2:file.txt # the version from HEAD. $ git show :3:file.txt # the version from MERGE_HEAD. ------------------------------------------------- When you ask linkgit:git-diff[1] to show the conflicts, it runs a three-way diff between the conflicted merge results in the work tree with stages 2 and 3 to show only hunks whose contents come from both sides, mixed (in other words, when a hunk's merge results come only from stage 2, that part is not conflicting and is not shown. Same for stage 3). The diff above shows the differences between the working-tree version of file.txt and the stage 2 and stage 3 versions. So instead of preceding each line by a single `+` or `-`, it now uses two columns: the first column is used for differences between the first parent and the working directory copy, and the second for differences between the second parent and the working directory copy. (See the "COMBINED DIFF FORMAT" section of linkgit:git-diff-files[1] for a details of the format.) After resolving the conflict in the obvious way (but before updating the index), the diff will look like: ------------------------------------------------- $ git diff diff --cc file.txt index 802992c,2b60207..0000000 --- a/file.txt +++ b/file.txt @@@ -1,1 -1,1 +1,1 @@@ - Hello world -Goodbye ++Goodbye world ------------------------------------------------- This shows that our resolved version deleted "Hello world" from the first parent, deleted "Goodbye" from the second parent, and added "Goodbye world", which was previously absent from both. Some special diff options allow diffing the working directory against any of these stages: ------------------------------------------------- $ git diff -1 file.txt # diff against stage 1 $ git diff --base file.txt # same as the above $ git diff -2 file.txt # diff against stage 2 $ git diff --ours file.txt # same as the above $ git diff -3 file.txt # diff against stage 3 $ git diff --theirs file.txt # same as the above. ------------------------------------------------- The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help for merges: ------------------------------------------------- $ git log --merge $ gitk --merge ------------------------------------------------- These will display all commits which exist only on HEAD or on MERGE_HEAD, and which touch an unmerged file. You may also use linkgit:git-mergetool[1], which lets you merge the unmerged files using external tools such as Emacs or kdiff3. Each time you resolve the conflicts in a file and update the index: ------------------------------------------------- $ git add file.txt ------------------------------------------------- the different stages of that file will be "collapsed", after which `git diff` will (by default) no longer show diffs for that file. [[undoing-a-merge]] === Undoing a merge If you get stuck and decide to just give up and throw the whole mess away, you can always return to the pre-merge state with ------------------------------------------------- $ git merge --abort ------------------------------------------------- Or, if you've already committed the merge that you want to throw away, ------------------------------------------------- $ git reset --hard ORIG_HEAD ------------------------------------------------- However, this last command can be dangerous in some cases--never throw away a commit you have already committed if that commit may itself have been merged into another branch, as doing so may confuse further merges. [[fast-forwards]] === Fast-forward merges There is one special case not mentioned above, which is treated differently. Normally, a merge results in a merge commit, with two parents, one pointing at each of the two lines of development that were merged. However, if the current branch is an ancestor of the other--so every commit present in the current branch is already contained in the other branch--then Git just performs a "fast-forward"; the head of the current branch is moved forward to point at the head of the merged-in branch, without any new commits being created. [[fixing-mistakes]] === Fixing mistakes If you've messed up the working tree, but haven't yet committed your mistake, you can return the entire working tree to the last committed state with ------------------------------------------------- $ git restore --staged --worktree :/ ------------------------------------------------- If you make a commit that you later wish you hadn't, there are two fundamentally different ways to fix the problem: 1. You can create a new commit that undoes whatever was done by the old commit. This is the correct thing if your mistake has already been made public. 2. You can go back and modify the old commit. You should never do this if you have already made the history public; Git does not normally expect the "history" of a project to change, and cannot correctly perform repeated merges from a branch that has had its history changed. [[reverting-a-commit]] ==== Fixing a mistake with a new commit Creating a new commit that reverts an earlier change is very easy; just pass the linkgit:git-revert[1] command a reference to the bad commit; for example, to revert the most recent commit: ------------------------------------------------- $ git revert HEAD ------------------------------------------------- This will create a new commit which undoes the change in HEAD. You will be given a chance to edit the commit message for the new commit. You can also revert an earlier change, for example, the next-to-last: ------------------------------------------------- $ git revert HEAD^ ------------------------------------------------- In this case Git will attempt to undo the old change while leaving intact any changes made since then. If more recent changes overlap with the changes to be reverted, then you will be asked to fix conflicts manually, just as in the case of <>. [[fixing-a-mistake-by-rewriting-history]] ==== Fixing a mistake by rewriting history If the problematic commit is the most recent commit, and you have not yet made that commit public, then you may just <>. Alternatively, you can edit the working directory and update the index to fix your mistake, just as if you were going to <>, then run ------------------------------------------------- $ git commit --amend ------------------------------------------------- which will replace the old commit by a new commit incorporating your changes, giving you a chance to edit the old commit message first. Again, you should never do this to a commit that may already have been merged into another branch; use linkgit:git-revert[1] instead in that case. It is also possible to replace commits further back in the history, but this is an advanced topic to be left for <>. [[checkout-of-path]] ==== Checking out an old version of a file In the process of undoing a previous bad change, you may find it useful to check out an older version of a particular file using linkgit:git-restore[1]. The command ------------------------------------------------- $ git restore --source=HEAD^ path/to/file ------------------------------------------------- replaces path/to/file by the contents it had in the commit HEAD^, and also updates the index to match. It does not change branches. If you just want to look at an old version of the file, without modifying the working directory, you can do that with linkgit:git-show[1]: ------------------------------------------------- $ git show HEAD^:path/to/file ------------------------------------------------- which will display the given version of the file. [[interrupted-work]] ==== Temporarily setting aside work in progress While you are in the middle of working on something complicated, you find an unrelated but obvious and trivial bug. You would like to fix it before continuing. You can use linkgit:git-stash[1] to save the current state of your work, and after fixing the bug (or, optionally after doing so on a different branch and then coming back), unstash the work-in-progress changes. ------------------------------------------------ $ git stash push -m "work in progress for foo feature" ------------------------------------------------ This command will save your changes away to the `stash`, and reset your working tree and the index to match the tip of your current branch. Then you can make your fix as usual. ------------------------------------------------ ... edit and test ... $ git commit -a -m "blorpl: typofix" ------------------------------------------------ After that, you can go back to what you were working on with `git stash pop`: ------------------------------------------------ $ git stash pop ------------------------------------------------ [[ensuring-good-performance]] === Ensuring good performance On large repositories, Git depends on compression to keep the history information from taking up too much space on disk or in memory. Some Git commands may automatically run linkgit:git-gc[1], so you don't have to worry about running it manually. However, compressing a large repository may take a while, so you may want to call `gc` explicitly to avoid automatic compression kicking in when it is not convenient. [[ensuring-reliability]] === Ensuring reliability [[checking-for-corruption]] ==== Checking the repository for corruption The linkgit:git-fsck[1] command runs a number of self-consistency checks on the repository, and reports on any problems. This may take some time. ------------------------------------------------- $ git fsck dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f ... ------------------------------------------------- You will see informational messages on dangling objects. They are objects that still exist in the repository but are no longer referenced by any of your branches, and can (and will) be removed after a while with `gc`. You can run `git fsck --no-dangling` to suppress these messages, and still view real errors. [[recovering-lost-changes]] ==== Recovering lost changes [[reflogs]] ===== Reflogs Say you modify a branch with <>, and then realize that the branch was the only reference you had to that point in history. Fortunately, Git also keeps a log, called a "reflog", of all the previous values of each branch. So in this case you can still find the old history using, for example, ------------------------------------------------- $ git log master@{1} ------------------------------------------------- This lists the commits reachable from the previous version of the `master` branch head. This syntax can be used with any Git command that accepts a commit, not just with `git log`. Some other examples: ------------------------------------------------- $ git show master@{2} # See where the branch pointed 2, $ git show master@{3} # 3, ... changes ago. $ gitk master@{yesterday} # See where it pointed yesterday, $ gitk master@{"1 week ago"} # ... or last week $ git log --walk-reflogs master # show reflog entries for master ------------------------------------------------- A separate reflog is kept for the HEAD, so ------------------------------------------------- $ git show HEAD@{"1 week ago"} ------------------------------------------------- will show what HEAD pointed to one week ago, not what the current branch pointed to one week ago. This allows you to see the history of what you've checked out. The reflogs are kept by default for 30 days, after which they may be pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn how to control this pruning, and see the "SPECIFYING REVISIONS" section of linkgit:gitrevisions[7] for details. Note that the reflog history is very different from normal Git history. While normal history is shared by every repository that works on the same project, the reflog history is not shared: it tells you only about how the branches in your local repository have changed over time. [[dangling-object-recovery]] ===== Examining dangling objects In some situations the reflog may not be able to save you. For example, suppose you delete a branch, then realize you need the history it contained. The reflog is also deleted; however, if you have not yet pruned the repository, then you may still be able to find the lost commits in the dangling objects that `git fsck` reports. See <> for the details. ------------------------------------------------- $ git fsck dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 ... ------------------------------------------------- You can examine one of those dangling commits with, for example, ------------------------------------------------ $ gitk 7281251ddd --not --all ------------------------------------------------ which does what it sounds like: it says that you want to see the commit history that is described by the dangling commit(s), but not the history that is described by all your existing branches and tags. Thus you get exactly the history reachable from that commit that is lost. (And notice that it might not be just one commit: we only report the "tip of the line" as being dangling, but there might be a whole deep and complex commit history that was dropped.) If you decide you want the history back, you can always create a new reference pointing to it, for example, a new branch: ------------------------------------------------ $ git branch recovered-branch 7281251ddd ------------------------------------------------ Other types of dangling objects (blobs and trees) are also possible, and dangling objects can arise in other situations. [[sharing-development]] == Sharing development with others [[getting-updates-With-git-pull]] === Getting updates with git pull After you clone a repository and commit a few changes of your own, you may wish to check the original repository for updates and merge them into your own work. We have already seen <> with linkgit:git-fetch[1], and how to merge two branches. So you can merge in changes from the original repository's master branch with: ------------------------------------------------- $ git fetch $ git merge origin/master ------------------------------------------------- However, the linkgit:git-pull[1] command provides a way to do this in one step: ------------------------------------------------- $ git pull origin master ------------------------------------------------- In fact, if you have `master` checked out, then this branch has been configured by `git clone` to get changes from the HEAD branch of the origin repository. So often you can accomplish the above with just a simple ------------------------------------------------- $ git pull ------------------------------------------------- This command will fetch changes from the remote branches to your remote-tracking branches `origin/*`, and merge the default branch into the current branch. More generally, a branch that is created from a remote-tracking branch will pull by default from that branch. See the descriptions of the `branch..remote` and `branch..merge` options in linkgit:git-config[1], and the discussion of the `--track` option in linkgit:git-checkout[1], to learn how to control these defaults. In addition to saving you keystrokes, `git pull` also helps you by producing a default commit message documenting the branch and repository that you pulled from. (But note that no such commit will be created in the case of a <>; instead, your branch will just be updated to point to the latest commit from the upstream branch.) The `git pull` command can also be given `.` as the "remote" repository, in which case it just merges in a branch from the current repository; so the commands ------------------------------------------------- $ git pull . branch $ git merge branch ------------------------------------------------- are roughly equivalent. [[submitting-patches]] === Submitting patches to a project If you just have a few changes, the simplest way to submit them may just be to send them as patches in email: First, use linkgit:git-format-patch[1]; for example: ------------------------------------------------- $ git format-patch origin ------------------------------------------------- will produce a numbered series of files in the current directory, one for each patch in the current branch but not in `origin/HEAD`. `git format-patch` can include an initial "cover letter". You can insert commentary on individual patches after the three dash line which `format-patch` places after the commit message but before the patch itself. If you use `git notes` to track your cover letter material, `git format-patch --notes` will include the comm