Question

I don’t see a difference between the output of ‘git format-patch’ and ‘git diff’, is there any? And won’t I be able to use ‘git diff’ to produce a patch and then apply it using git apply?

My problem is that I have changes added to the index, but apparently git format-patch only accepts commits, so if I can use the output of diff, then I can use this command to produce a patch for the changes in the index:

git diff --cached > index.patch

Answer 1

A patch created with git format-patch will also include some meta-information about the commit (committer, date, commit message, …) and will contains diff of binary data. Everything will be formatted as a mail, so that it can be easily sent. The person that receive it can then recreate the corresponding commit with git am and all meta-data will be intact. It can also be applied with git apply as it is a super-set of a simple diff.

A patch crated with git diff will be a simple diff with context (think diff -u). It can also be applied with git apply but the meta-data will not be recreated (as they are not present).

In summary, git format-patch is useful to transmit a commit, while git diff is useful to get a diff between two trees.