variable `GIT_EDITOR=:` if the command will not bring up an editor
to modify the commit message.
+prepare-commit-msg
+------------------
+
+This hook is invoked by `git-commit` 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 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 SHA1 (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 replacement for pre-commit hook.
+
+The sample `prepare-commit-msg` hook that comes with git comments
+out the `Conflicts:` part of a merge's commit message.
+
commit-msg
----------