Git: Using Patch Files to Share Code Changes Without Branches or Commits

I recently learned a nice little trick that has come in handy in a few situations already! 🤓

Sometimes we want to share changes to one or more files in a git repository that are temporary and don't warrant their own branch or commit.

For example, we might want to share a line of code that throws an error in a certain place to test error handling:

// api.js
async function fetchUser() {
	throw new Error('User not found')
	const { user } = await api.get('/users/me')

	return user
}

If you run git diff, you can see the one-line-change:

diff --git a/api.js b/api.js
index 98293fe..820a715 100644
--- a/api.js
+++ b/api.js
@@ -1,4 +1,5 @@
 async function fetchUser() {
+    throw new Error('User not found')
     const { user } = await api.get('/users/me')
     return user

To share this exact change with somebody else, we can simply store the output of git diff in a file:

$ git diff api.js > simulate-error.patch

We can then send that file to a colleague, who can apply it using git apply:

$ git apply simulate-error.patch

Note that git apply needs to be run from the root of the repository!

You can also upload the patch-file to a Gist for example (quickly create one with gist.new) so it can be applied like so (using the file's raw URL):

$ curl https://gist.githubusercontent.com/.../simulate-error.patch | git apply

Bonus Tip: GitHub Pull Requests as Raw Patch Files

Thanks to my Twitter friend Max (he has the exact same name as me, don't be confused ^_^) for this tip:

You can add ".patch" to a pull request's URL and it will give you a raw patch-file that contains all the changes in that PR.

E.g. opening

https://github.com/microsoft/playwright/pull/7644.patch

in your browser will redirect you to

https://patch-diff.githubusercontent.com/raw/microsoft/playwright/pull/7644.patch

which is a patch-file. 🔥