How do I compare a file in git with another revision of another file?

Question

I have a file called file.txt. I copy it, call it fileOld.txt and make some small changes. I then make bigger changes to file.txt. I have not committed anything.

How can I see what changes I made in fileOld.txt, ie. how can I compare fileOld.txt with the latest committed version of file.txt?

The best I've come up with so far is:

diff -u <(git show origin/HEAD:file.txt) fileOld.txt

which is fine, but I wondered if git supported this directly somehow?

Answer 1

This diffs file1.txt from the previous commit to your current file2.txt.

git diff HEAD^:file1.txt file2.txt

You can ofcourse replace HEAD^ with the commit SHA1.