When maintaining a project sooner or later there comes the time when you need to apply patches that have been submitted to you. Assuming a patch-based workflow those are going to be one patch per mail, possibly connected in a thread. There's lots of different ways of getting those patches to their final destination, git-am(1), and in this post I want to take a look at ones that work well with mutt(1) or neomutt(1) since that is what I use.

I want to rely on the default bindings as much as possible. All mentioned bindings should work out of the box.

Applying a single patch is very straightforward: Select the mail in the pager and hit | to pipe it to an external command. This command will be some variation of git-am(1), perhaps git am -s to also add a Signed-off-by trailer.

What if you want to apply a patch series, however? An obvious solution would be to pipe each message in the thread to git-am(1). The <pipe-message> command we invoked earlier with | only applies to the currently selected message, so we can't use that on the whole thread. Instead we can tag the whole thread using <Esc>t, then use the <tag-prefix> command ; followed by | to send all tagged messages to git-am(1).

There's two problems with this, though. The first is that depending on the setting of pipe_split, git-am(1) might only apply the first patch in the series. This is the case if pipe_split is set to the default of no; mutt(1) will then concatenate the messages before sending them to the external command. Sadly this concatenated format is slightly different from the mbox format that git-am(1) expects, making it not see anything past the first patch.

With pipe_split set to yes, mutt(1) spawns one process per tagged mail instead, applying all patches correctly. Now that git-am(1) is spawned once per mail, however, you lose its atomicity: Neither ORIG_HEAD will be set correctly, nor will --abort go back to the original branch.

This might not be a big issue, but I am not a fan. Thankfully git-am(1) supports reading patches from mbox files or Maildir structures. So instead of piping mails to git-am(1) via <pipe-message>, let's save them to the current directory: With the thread still tagged, ;C (<tag-prefix> followed by <copy-message>) will save a copy of it under a given path. Now you can apply the series by hitting ! and running git am -s <path>. This works with mbox_type set to either mbox or Maildir (but see № 9 ).

Of course there is no need to rely on the default bindings, especially if you need to do this kind of thing very often. mutt(1) is easily customizable, making it possible to bind the entire chain of actions to just one keystroke. If you're interested in a more detailed examination of a patch-based workflow with mutt(1), check out this post by Greg Kroah-Hartman.