Personally I soldiered on to to the point of being able to extract objects from packfiles, before I realised just how monstrously and tediously complex `git rev-parse` is, and gave up. It's foundational to pretty much every porcelain command, so it's not really something you can leave out if you want a semi-functioning `git`. See https://git-scm.com/docs/git-rev-parse#_specifying_revisions and https://github.com/git/git/blob/ee48e70a829d1fa2da82f1478705... ; `git` really is an edifice.