Find Git commit given just a version of file

Question

If you only have a file (only contains text data), how can you determine which commit in history it maps to?

This is useful for finding a version of a project when someone has ripped a subset of the files out of the repository and dumped them somewhere.

Answer 1

1) Iterate through all the objects in the repository (.git/objects/*), diff each file (using git cat-file) with your given file

2) When you have found the SHA of the object that matches the input file, find the commit containing that file's SHA. Iterate through all commits and use git ls-tree | grep to find which commit contains the object.

I consolidated this solution into a simple, easy-to-run script here: https://gist.github.com/themattman/20ec6da84304740972e057c22b15c0ee