Git Hooks for Commit and Merge Operations

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 linkgit:git-commit[1], and can be bypassed with the `--no-verify` option. It takes no parameters, and is invoked before obtaining the proposed commit log message and making a commit. Exiting with a non-zero status from this script causes the `git commit` command to abort before creating a commit. The default 'pre-commit' hook, when enabled, catches introduction of lines with trailing whitespaces and aborts the commit when such a line is found. All the `git commit` hooks are invoked with the environment variable `GIT_EDITOR=:` if the command will not bring up an editor to modify the commit message. The default 'pre-commit' hook, when enabled--and with the `hooks.allownonascii` config option unset or set to false--prevents the use of non-ASCII filenames. pre-merge-commit ~~~~~~~~~~~~~~~~ This hook is invoked by linkgit:git-merge[1], and can be bypassed with the `--no-verify` option. It takes no parameters, and is invoked after the merge has been carried out successfully and before obtaining the proposed commit log message to make a commit. Exiting with a non-zero status from this script causes the `git merge` command to abort before creating a commit. The default 'pre-merge-commit' hook, when enabled, runs the 'pre-commit' hook, if the latter is enabled. This hook is invoked with the environment variable `GIT_EDITOR=:` if the command will not bring up an editor to modify the commit message. If the merge cannot be carried out automatically, the conflicts need to be resolved and the result committed separately (see linkgit:git-merge[1]). At that point, this hook will not be executed, but the 'pre-commit' hook will, if it is enabled. prepare-commit-msg ~~~~~~~~~~~~~~~~~~ This hook is invoked by linkgit:git-commit[1] right after preparing the default log message, and before the editor is started. It takes one to three parameters. The first is the name of the file that contains the commit log message. The second is the source of the commit message, and can be: `message` (if a `-m` or `-F` option was given); `template` (if a `-t` option was given or the configuration option `commit.template` is set); `merge` (if the commit is a merge or a `.git/MERGE_MSG` file exists); `squash` (if a `.git/SQUASH_MSG` file exists); or `commit`, followed by a commit object name (if a `-c`, `-C` or `--amend` option was given). If the exit status is non-zero, `git commit` will abort. The purpose of the hook is to edit the message file in place, and it is not suppressed by the `--no-verify` option. A non-zero exit means a failure of the hook and aborts the commit. It should not be used as a replacement for the pre-commit hook. The sample `prepare-commit-msg` hook that comes with Git removes the help message found in the commented portion of the commit template. commit-msg ~~~~~~~~~~ This hook is invoked by linkgit:git-commit[1] and linkgit:git-merge[1], and can be bypassed with the `--no-verify` option. It takes a single parameter, the name of the file that holds the proposed commit log message. Exiting with a non-zero status causes the command 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. 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` trailers, and aborts the commit if one is found. post-commit ~~~~~~~~~~~ This hook is invoked by linkgit:git-commit[1]. It takes no parameters, and is invoked after a commit is made. This hook is meant primarily for notification, and cannot affect the outcome of `git commit`. pre-rebase ~~~~~~~~~~ This hook is called by linkgit:git-rebase[1] and can be used to prevent a branch from getting rebased.

Git provides various hooks for commit and merge operations, including pre-commit, pre-merge-commit, prepare-commit-msg, commit-msg, and post-commit, which can be used to enforce project standards, run tests, and perform other automated tasks. These hooks can be bypassed with the --no-verify option and can exit with a non-zero status to abort the command. They can edit the commit message, refuse the commit, or prevent a branch from getting rebased, and are invoked at different points during the Git workflow, providing flexibility and customization options for repository management.