git-annex-lookupkey man page
git-annex-lookupkey — looks up key used for file
git annex lookupkey [file ...]
This plumbing-level command looks up the key used for a file in the index. The key is output to stdout. If there is no key (because the file is not present in the index, or is not a git-annex managed file), nothing is output, and it exits nonzero.
Enable batch mode, in which a line containing the filename is read from stdin, the key is output to stdout (with a trailing newline), and repeat.
Note that if there is no key corresponding to the file, an empty line is output to stdout instead.
Joey Hess <email@example.com>