stg-id(1) Manual Page

Print the SHA1 value of a Git id (defaulting to HEAD). In addition to the standard Git id’s like heads and tags, this command also accepts [<branch>:]<patch> for the id of a patch, [<branch>:]{base} for the base of the stack and [<branch>:]{public} for the public branch corresponding to the stack (see the publish command for details). If no branch is specified, it defaults to the current one. The bottom of a patch is accessible with the [<branch>:]<patch>^ format.

Part of the StGit suite - see stg(1)