get the latest commit where a file changed

Question

My task at hand is to figure out, what is the commit id of the last commit, where a specific file changed. I'm using ruby / rugged. The only solution I came up with is to walk over all commits, search for the file in the tree associated with the commit for that file and compare that files oid with the oid of the file from the first (latest) commit:

def commit_oid commit, file
    commit.tree.walk( :postorder ) { | root, obj |
        return obj[ :oid ] if "#{root}#{obj[ :name ]}" == file 
    }

    raise "\'#{file}\' not found in repository"     
end

def find_last_commit file
    johnny = Rugged::Walker.new( get_repository )
    johnny.push get_repository.head.target

    oid = commit_oid johnny.first, file
    old_commit = johnny.first.oid

    johnny.each do | commit |
        new_oid = commit_oid commit, file

        return old_commit if new_oid != oid

        old_commit = commit.oid 
    end

    old_commit
end

This works but seems to be quit complicated. There must be an easier ways to get the information, "what changed with a commit". Is there an easier, more straight forward way to accomplish the same?

Answer 1

Running $ git log <file> will give you a reverse chronological log of only commits that altered the given file. $ git whatchanged <file> will do the same, adding a line with details of the change (i.e. mode change, change type). It's great for visual purposes, but not so much for scripting.

If you want just the hash of the most recent commit, the following will work well: $ git rev-list --max-count 1 HEAD <file>