Hooks are little scripts you can place in $GIT_DIR/hooks directory to trigger action at certain points. When git-init is run, a handful example hooks are copied in the hooks directory of the new repository, but by default they are all disabled. To enable a hook, make it executable with chmod +x.

This document describes the currently defined hooks.

applypatch-msg

This hook is invoked by git-am script. It takes a single parameter, the name of the file that holds the proposed commit log message. Exiting with non-zero status causes git-am to abort before applying the patch.

The hook is allowed to edit the message file in place, and can be used to normalize the message into some project standard format (if the project has one). It can also be used to refuse the commit after inspecting the message file.

The default applypatch-msg hook, when enabled, runs the commit-msg hook, if the latter is enabled.

pre-applypatch

This hook is invoked by git-am. It takes no parameter, and is invoked after the patch is applied, but before a commit is made. Exiting with non-zero status causes the working tree after application of the patch not committed.

It can be used to inspect the current working tree and refuse to make a commit if it does not pass certain test.

The default pre-applypatch hook, when enabled, runs the pre-commit hook, if the latter is enabled.

post-applypatch

This hook is invoked by git-am. It takes no parameter, and is invoked after the patch is applied and a commit is made.

This hook is meant primarily for notification, and cannot affect the outcome of git-am.

pre-commit

This hook is invoked by git-commit, and can be bypassed with \--no-verify option. It takes no parameter, and is invoked before obtaining the proposed commit log message and making a commit. Exiting with non-zero status from this script causes the git-commit to abort.

The default pre-commit hook, when enabled, catches introduction of lines with trailing whitespaces and aborts the commit when such a line is found.

commit-msg

This hook is invoked by git-commit, and can be bypassed with \--no-verify option. It takes a single parameter, the name of the file that holds the proposed commit log message. Exiting with non-zero status causes the git-commit to abort.

The hook is allowed to edit the message file in place, and can be used to normalize the message into some project standard format (if the project has one). It can also be used to refuse the commit after inspecting the message file.

The default commit-msg hook, when enabled, detects duplicate "Signed-off-by" lines, and aborts the commit if one is found.

post-commit

This hook is invoked by git-commit. It takes no parameter, and is invoked after a commit is made.

This hook is meant primarily for notification, and cannot affect the outcome of git-commit.

pre-receive

This hook is invoked by git-receive-pack on the remote repository, which happens when a git push is done on a local repository. Just before starting to update refs on the remote repository, the pre-receive hook is invoked. Its exit status determines the success or failure of the update.

This hook executes once for the receive operation. It takes no arguments, but for each ref to be updated it receives on standard input a line of the format:

<old-value> SP <new-value> SP <ref-name> LF

where <old-value> is the old object name stored in the ref, <new-value> is the new object name to be stored in the ref and <ref-name> is the full name of the ref. When creating a new ref, <old-value> is 40 0.

If the hook exits with non-zero status, none of the refs will be updated. If the hook exits with zero, updating of individual refs can still be prevented by the update hook.

Both standard output and standard error output are forwarded to git-send-pack on the other end, so you can simply echo messages for the user.

update

This hook is invoked by git-receive-pack on the remote repository, which happens when a git push is done on a local repository. Just before updating the ref on the remote repository, the update hook is invoked. Its exit status determines the success or failure of the ref update.

The hook executes once for each ref to be updated, and takes three parameters:

A zero exit from the update hook allows the ref to be updated. Exiting with a non-zero status prevents git-receive-pack from updating that ref.

This hook can be used to prevent forced update on certain refs by making sure that the object name is a commit object that is a descendant of the commit object named by the old object name. That is, to enforce a "fast forward only" policy.

It could also be used to log the old..new status. However, it does not know the entire set of branches, so it would end up firing one e-mail per ref when used naively, though. The post-receive hook is more suited to that.

Another use suggested on the mailing list is to use this hook to implement access control which is finer grained than the one based on filesystem group.

Both standard output and standard error output are forwarded to git-send-pack on the other end, so you can simply echo messages for the user.

The default update hook, when enabled—and with hooks.allowunannotated config option turned on—prevents unannotated tags to be pushed.

post-receive

This hook is invoked by git-receive-pack on the remote repository, which happens when a git push is done on a local repository. It executes on the remote repository once after all the refs have been updated.

This hook executes once for the receive operation. It takes no arguments, but gets the same information as the pre-receive hook does on its standard input.

This hook does not affect the outcome of git-receive-pack, as it is called after the real work is done.

This supersedes the post-update hook in that it gets both old and new values of all the refs in addition to their names.

Both standard output and standard error output are forwarded to git-send-pack on the other end, so you can simply echo messages for the user.

The default post-receive hook is empty, but there is a sample script post-receive-email provided in the contrib/hooks directory in git distribution, which implements sending commit emails.

post-update

This hook is invoked by git-receive-pack on the remote repository, which happens when a git push is done on a local repository. It executes on the remote repository once after all the refs have been updated.

It takes a variable number of parameters, each of which is the name of ref that was actually updated.

This hook is meant primarily for notification, and cannot affect the outcome of git-receive-pack.

The post-update hook can tell what are the heads that were pushed, but it does not know what their original and updated values are, so it is a poor place to do log old..new. The post-receive hook does get both original and updated values of the refs. You might consider it instead if you need them.

When enabled, the default post-update hook runs git-update-server-info to keep the information used by dumb transports (e.g., HTTP) up-to-date. If you are publishing a git repository that is accessible via HTTP, you should probably enable this hook.

Both standard output and standard error output are forwarded to git-send-pack on the other end, so you can simply echo messages for the user.