I have two repositories. In one, I make changes to file ./hello.test. I commit the changes and create a patch from that commit with git format-patch -1 HEAD. Now, I have a second repository that contains a file that has the same contents as hello.test but is placed in a different directory under a different name: ./blue/red/hi.test. How do I go about applying the aforementioned patch to the hi.test file? I tried git am --directory='blue/red' < patch_file but that of course complains that the files are not named the same (which I thought Git didn't care about?). I know I could probably edit the diff to apply to that specific file but I'm looking for a command solution.
There is a simple solution that does not involve manual patch editing nor external script.
In the first repository (this may also export a range of commit, use -1 if you want to select only one commit) :
git format-patch --relative <committish> --stdout > ~/patch
In the second repository :
git am --directory blue/red/ ~/patch
Instead of using --relative in git format-patch, another solution is to use -p<n> option in git am to strip n directories from the path of the patches, as mentioned in a answer to a similar question.
It is also possible to run git format-patch --relative <committish> without the --stdout, and it will generate a set of .patch files. These files can then be fed directly to git am with git am --directory blue/red/ path/to/*.patch.
Answering my own question with a script that does just this: https://github.com/mprpic/apply-patch-to-file
Rather than modifying the patch file manually, it prompts the user for the target file, modifies the patch, and applies it to the repo you're currently in.
Building upon the answer by @georgebrock, here's a solution I used:
First, create the patch files as usual (eg. git format-patch commitA..commitB).
Then make sure that your target repository is clean (there should be no changed or untracked files) and apply the patches like this:
cd second-repo
git am ~/00*.patch
For every patch file you will get an error like "error: XYZ does not exist in index". You can now apply this patch file manually:
patch --directory blue/red < ~/0001-*.patch
git add -a
git am --continue
You have to do these three steps for each patch file.
This will preserve the original commit message etc. without requiring any special git format-patch command or editing the patch files.
I understand the two files are exactly the same in your situation, thus the patch is likely to succeed.
However, in case you want to apply a patch to a similar, but not exactly the same file, or you want to do an interactive patching, you will use three way merge.
Say you modified File A, let's denote A~1 as the previous version, and you want to apply the diff between A~1 to A to File B.
Open a three way merge tool, for instance Beyond Compare, the path of left panel is A, middle panel is the common ancestor so the path is A~1, the path of right panel is B. Then, the lower panel shows the result of applying the diff between A~1 to A to File B.
The following figure illustrates the idea.
来源：https://stackoverflow.com/questions/16526321/how-to-apply-a-git-patch-to-a-file-with-a-different-name-and-path