How do you compare two revisions of a file, or your current file and a previous revision?

Compare command is git diff.

To compare 2 revisions of a file:

$ git diff <commit1> <commit2> <file_name>

That diffs commit1 against commit2; if you change order then files are diffed the other way round, which may not be what you expect...

To compare current staged file against the repository:

$ git diff --staged <file_name>

To compare current unstaged file against the repository:

$ git diff <file_name>