A commit SHA or some other identifier that ultimately dereferences to a commit/tree.
HEAD is the local HEAD, and index is the the staged. If not specified,
then index will be used instead. But this can be HEAD~2 or ed14ef1~1 where ed14ef1 is a commit hash.
The desired encoding which should be used when retrieving the file content.
utf8 should be used for text content and binary for blobs. The default one is utf8.
Options for further refining the
git showcommand.