Apply patches created with git log -p

Question

I have a file of patches (all of which apply to a single file) generated with

git log -p file-of-interest.txt >patches.txt

Now I want to apply these patches in another repo, but when I try

git am patches.txt

I get the error message "Patch format detection failed."

(git apply does not work either). Which is the correct way to apply these patches?

Edit: What I want to do is to extract all changes to a single file between two commits into a set of patches, and then apply those changes in another repo. git log -p from..to -- the-file will generate the diff. If it is not possible to apply the patch from git log, is it possible to make format-patch (or another command) generate the patches for only a single file?

Answer 1

You need to break the patches down into individual patches. You could do that manually from your git log -p output, then use git apply to apply them in sequence. git log -p output wasn't really intended for git to process...

But a better option would be to use git format-patch to create the sequence of patch files for you (no manual splitting needed), then use git am to apply them all in one go...

git format-patch -o <output_directory> <from_revision>..<to_revision> -- file-of-interest.txt

Also note that git am expects email-formatted patches (like those produced by git format-patch, which is why you get "Patch format detection failed"). Patches generated with diff or git diff should be applied with git apply, not git am. But the git format-patch / git am workflow is more flexible and generally more robust.

Answer 2

If you format the hash resulting from git log prepending the number of the path with the "-" symbol then all the patchs can be generated at once in different files. Example:

git format-patch $(git log --reverse 073dd505f..fff28ff65 --pretty="%H" -- the/needed/path | awk '{print -NR, " ", $0}')

That will cover all the filter that you can apply from git log. They are not allways consecutive commits. For example taking the patchs corresponding to a given user:

git format-patch $(git log --reverse --author="John Doe" --pretty="%H" -- the/needed/path | awk '{print -NR, " ", $0}')

The --reverse option is needed to give you the patch in chronological order, because git log give the most recents first.