PathFingerprint allows you to recursively generate hashes for a directory structure. While doing this, it builds a catalog in a separate directory to serve as a cache. Subsequent runs of large directories will run much quicker. You can also do simple lookups against an existing catalog and generate/print a report of what has changed since the last run.

Build a test directory:

$ mkdir -p scan_path/subdir1
$ mkdir -p scan_path/subdir2
$ touch scan_path/subdir1/aa
$ touch scan_path/subdir1/bb

Calculate the hash (with reporting enabled):

$ pfhash -s scan_path -c catalog_path -R - 
create file subdir1/aa
create file subdir1/bb
create path subdir1
create path subdir2
create path .
0df9bc5a7657b7d481c219656441f10d21fd5668

Run again with a couple of changes (with reporting enabled):

$ touch scan_path/subdir1/aa
$ touch scan_path/subdir2/new_file

$ pfhash -s scan_path -c catalog_path -R - 
update file subdir1/aa
create file subdir2/new_file
update path subdir2
update path .
e700843c1b5c2f40a68098e1df96ef08b6081fe8

Lookup the hash using the lookup tool:

$ pflookup -c catalog_path
e700843c1b5c2f40a68098e1df96ef08b6081fe8

$ pflookup -c catalog_path -r subdir1
426a98d313a0a740b8445daa5102b3ed6dd7f4ed

$ pflookup -c catalog_path -r subdir1/aa
da39a3ee5e6b4b0d3255bfef95601890afd80709