Git: How to diff two different files in different commits?

Question

I have a repository where a number of files have been renamed from .html to .php and further edited in a number of commits since my last pull. Using git diff to shows all the html contents removed and all the php content added. Is there a neat way to have git diff detect the renames (something like git log --follow does), or directly compare different filenames across different commits (something like the solution in Git: How to diff two different files in different branches? , but for commits)?

Answer 1

You can always compare 2 files in 2 different commits:

git diff commit1:file1_path commit2:file2_path 

Answer 2

As said previously, the format needed is:

$ git diff commit1:file1_path commit2:file2_path 

But there are a couple gotchas:

XXX$ git diff file1_path commit2:file2_path 

This will not work, even if file1_path is in HEAD; if you want to specify a commit for one file you must specify it for both. This will attempt to interpret "commit2:file2_path" as a file path with the first directory it steps into being, e.g., HEAD^:foo/. This will rarely exist so it generally gives an informative error message. (Note: @philh says that git diff commit1:file1_path file2_path works fine, but I haven't confirmed that myself.)

file1_path format: The paths given will be treated as relative to the repository's root. Absolute paths are not permitted, and relative paths must be explicit. For a concrete example; say your directory structure looks like the below, and your working directory is ~/repo/proj:

~/repo   .git   proj     tests       foo         bar.sh     utils       baz         quux.sh 

If you are trying to compare HEAD^:(...)/bar.sh to HEAD:(...)/quux.sh, the only permissible paths for bar.sh are:

• proj/tests/foo/bar.sh
• ./tests/foo/bar.sh

The explicit relative path with ./ works, but the more common implicit path tests/foo/bar.sh will not work. That version will sometimes fail silently - I think this is based on the format used in the other arguments but I'm not sure. Absolute paths will also not work; ~/repo/proj/tests/foo/bar.sh and /home/username/repo/proj/tests/foo/bar.sh will fail. AFAICT that will never fail silently.