I had two copies of a collection of large files (a library of TV episodes). The files in one copy had been carefully renamed; the other collection had inconsistent filenames. I wanted to make the filenames match in both places. dumbhash and dumbmv are my solution to this problem. dumbhash generates an md5sum(1)-like listing of the MD5 hashes of the first 512KB of a collection of files. dumbmv compares the hashes between two such listings (a source and a target), and renames the files from the source listing to match the corresponding names from the target.

For example:

machine-a$ ./dumbhash archive/* | tee targets.txt
d8c0e766502bb5e19faaebd035d478ac  archive/file-a
eaef8aa1ecec72410dbe14141e2c6c88  archive/file-b
machine-a$ scp targets.txt machine-b:

machine-b$ ./dumbhash archive/* | tee sources.txt
d8c0e766502bb5e19faaebd035d478ac  archive/a.1080p.WEB-DL.DD5.1.h264-See
eaef8aa1ecec72410dbe14141e2c6c88  archive/b.1080p.WEB-DL.DD5.1.h264-See
machine-b$ ./dumbmv sources.txt targets.txt
Renaming "archive/a.1080p.WEB-DL.DD5.1.h264-See" to "archive/file-a".
Renaming "archive/b.1080p.WEB-DL.DD5.1.h264-See" to "archive/file-b".

Files missing from either side are ignored.

dumbln came about later as the solution to a similar but slightly different problem: I had two copies of a collection of large files (a download directory and a media directory), and I wanted to hard-link duplicates to each other to reduce disk usage. dumbln compares the hashes between one or more dumbhash listings and replaces all of the paths for duplicate data with links to the same inode. It will keep inode with the lowest number, and reset its mtime/atime to be the min/max of the mtimes/atimes of all of the duplicates.

For example:

$ ./dumbhash downloads/* | tee downloads.txt
d8c0e766502bb5e19faaebd035d478ac  downloads/a.1080p.WEB-DL.DD5.1.h264-See
$ ./dumbhash media/* | tee media.txt
d8c0e766502bb5e19faaebd035d478ac  media/file-a
$ ./dumbln downloads.txt media.txt
Linking "downloads/a.1080p.WEB-DL.DD5.1.h264-See" to "media/file-a".

Unique files are ignored, as are files where all paths already point to the same inode.

Put the dumbhash, dumbln, and dumbmv scripts somewhere on your PATH, and make sure they're marked as executable.

$ sudo install -v -m 0755 dumb* /usr/local/bin
install: dumbhash -> /usr/local/bin/dumbhash
install: dumbln -> /usr/local/bin/dumbln
install: dumbmv -> /usr/local/bin/dumbmv

dumbhash is a POSIX shell script. It depends on cut, dd, and md5sum.

dumbmv and dumbln are Python 3 scripts. They depend only on the Python standard library.

Having identified the need for a rename operation, dumbmv directly calls the Python os.rename() library function. This has two caveats:

• The parent directory of the destination filename must already exist. It will not be automatically created. This was fine for me, because I was moving files around within existing directories.
• os.rename() only works when the source and destination are on the same filesystem. I specifically wanted to avoid accidental copying, but you may need to modify the script to use shutil.move() instead.

If the same hash appears multiple times in either dumbmv input file, only the last occurrence will be considered. dumbln shouldn't have this problem.

Why is dumbhash necessary? Why not just feed the output of standard md5sum(1) into dumbmv/dumbln?

Because these are big files, and my hard drives are slow, and I'm impatient.

I have small files, and my hard drives are fast, and I'm patient. Can I feed the output of standard md5sum(1) into dumbmv/dumbln?

Yes, that should work correctly, as dumbhash mimics the output format of md5sum. Similarly, you should be able to use the output of any other checksumming tool that produces the same output format: sha256sum, b2sum, etc.

MD5 hashes are not cryptographically secure!

That's not a question.

They are fast, though, and when I'm only considering the first 512KB of the file anyway, I'm clearly not worried about collisions.