git get-tar-commit-id < <tarfile>
Acts as a filter, extracting the commit ID stored in archives created by git archive. It reads only the first 1024 bytes of input, thus its runtime is not influenced by the size of <tarfile> very much.
If no commit ID is found, git get-tar-commit-id quietly exists with a return code of 1. This can happen if <tarfile> had not been created using git archive or if the first parameter of git archive had been a tree ID instead of a commit ID or tag.
Part of the git(1) suite