Is there a way to see what files have changed in a branch?
For some reason no one mentioned git-tree. See https://stackoverflow.com/a/424142/1657819
git-tree is preferred because it's a plumbing command; meant to be programmatic (and, presumably, faster)
(assuming base branch is master)
git diff-tree --no-commit-id --name-only -r master..branch-name
However this will show you all files which were affected in the branch, if you want to see explicitly modified files only, you can use --diff-filter:
git diff-tree --no-commit-id --name-only -r master..branch-name --diff-filter=M
Also one can use --name-status instead of --name-only to see the status of the files (A/M/D and so on)