Git patch

Patches

See this very nice post!

Make some work

git checkout -b fix

In the new fix branch you can hack whatever you need to fix. Write tests, update code etc. etc.

# To only add updated files to commit stage
git add -u
# To make a commit
git commit -m "my commit message"

When you’re satisfied with all you changes, it’s time to create your patch. We assume you made a few commits in the fix branch and did not yet merge it back in to the master branch.

Check you changes

git log
git log --pretty=oneline -5

Create patches

Now create your patch, comparing to the master branch

git format-patch master --ignore-if-in-upstream

Now tar and gunzip the files

tar -cvzf fix.patch.tar.gz 00*.patch
rm 00*.patch

If you need to unpack (ungzip, unarchive) a tar.gz file

tar -xzf fix.patch.tar.gz

Normally, git would create a separate patch file for each commit, but that’s not what we want. All we need is a single patch file. This will create a new file fix.patch with all changes from the current branch (fix) against master.

Create one patch file, comparing to the master branch

git format-patch master --stdout --ignore-if-in-upstream > fix.patch

Now, you have a patch for the fix you wrote. Send it to the maintainer of the project.

Applying the patch

In subversion

 patch -p1 < fix.patch

In git

The maintainer will take some steps, to check everything goes smooth.
First, we take a look at what changes are in the patch. You can do this easily with git apply.

git apply --stat fix.patch

This command does not apply the patch, but only shows you the stats about what it’ll do.
After peeking into the patch file with your favorite editor, you can see what the actual changes are.

Next, you’re interested in how troublesome the patch is going to be. Git allows you to test the patch before you actually apply it.

git checkout master
git apply --check fix.patch

If you don’t get any errors, the patch can be applied cleanly.
Otherwise you may see what trouble you’ll run into.

To apply the patch, I’ll use git am instead of git apply.
The reason for this is that git am allows you to sign off an applied patch. This may be useful for later reference.

git am --signoff < fix.patch

Applying: Added specs to test empty poster URL behaviour
Applying: Added poster URL as part of cli output

Okay, patches were applied cleanly and you’re master branch has been updated. Of course, run your tests again to make sure nothing got borked.

In you git log, you’ll find that the commit messages contain a “Signed-off-by” tag.
This tag will be read by Github and others to provide useful info about how the commit ended up in the code.