---
title: Send A Patch To Someone Using `git format-patch`
teaser: Use Git's built-in functionality for sharing a patch without a centralized
  server.
tags: git
author: Prem Sichanugrist
published_on: 2016-02-25
---

[Git] is designed to be a distributed version control system. You can actually
send a patch for someone to review without the need to have a centralized Git
repository using the `git format-patch` feature. This is very useful when your
remote Git repository is down.

[Git]: https://git-scm.com/

## Preparing a patch

When you're ready to send the changes, use `git format-patch [BASE_BRANCH_NAME]`:

    $ git format-patch master
    0001-Update-build-matrix.patch
    0002-Display-current-gemfile-when-run-bundle-update.patch

Since my feature branch is two commits ahead of `master`, Git creates two files,
one for each commit. If you inspect the file, you will see the changes alongside
your commit message:

    From b2df28155560c68772063df3b3250d811e66f35e Mon Sep 17 00:00:00 2001
    From: Prem Sichanugrist <prem@example.com>
    Date: Mon, 25 Jan 2016 18:18:38 -0500
    Subject: [PATCH 1/2] Update build matrix

    Build Appraisal against these versions of Ruby

    ... snip ...

    ---
     .travis.yml | 13 ++++++-------
     1 file changed, 6 insertions(+), 7 deletions(-)

    diff --git a/.travis.yml b/.travis.yml
    index 6b56084..52d0bff 100644
    --- a/.travis.yml
    +++ b/.travis.yml
    @@ -3,12 +3,12 @@ sudo: false
     before_install: gem install bundler

     rvm:
    -  - 1.8
    -  - 1.9
    -  - 2.0
    -  - 2.1

    ... snip ...

    --
    2.7.0

If you want to create just one file, to more easily use as an attachment or
upload somewhere else, you can use the `--stdout` option and redirect the output
to a file:

    $ git format-patch master --stdout > new-feature.patch
    $ cat new-feature.patch

    From b2df28155560c68772063df3b3250d811e66f35e Mon Sep 17 00:00:00 2001
    From: Prem Sichanugrist <prem@example.com>
    Date: Mon, 25 Jan 2016 18:18:38 -0500
    Subject: [PATCH 1/2] Update build matrix

    Build Appraisal against these versions of Ruby

    ... snip ...

    --
    2.7.0


    From 54c7c4b5df552ef7540d4612c17dbbcc1079f47c Mon Sep 17 00:00:00 2001
    From: Prem Sichanugrist <prem@example.com>
    Date: Mon, 25 Jan 2016 18:14:06 -0500
    Subject: [PATCH 2/2] Display current gemfile when run `bundle update`

    This is done by setting `gemfile` setting directly and not through
    `BUNDLE_GEMFILE` setting.
    ---

    ... snip ...

While it's possible to use `git diff` and pipe the changes to a file, I think
`git format-patch` is a better way because it includes the commit message
describing the changes you made.

## To review a patch

When you receive a patch file from someone, you can easily apply the patch using
the `git am` command:

```bash
# Checkout to a new branch
$ git checkout review-new-feature

# If you received the patch in a single patch file
$ cat new-feature.patch | git am

# If you received multiple patch files
$ cat *.patch | git am

# Check the result
$ git log --oneline
6787572 Display current gemfile when run `bundle update`
928928c Update build matrix
...
```

Note that the SHA of the patch that you merge with `git am` will not be the same
SHA. However, the commit message will be intact.

If you are just getting started using Git, be sure to check out our new book
titled [Goal-Oriented Git] which is currently in beta. It will help you get up
to speed on how to use Git on your day-to-day work. If you are already feeling
confident, you can check out our [Mastering Git] trail on [Upcase] which should
help you on your path towards becoming a Git expert. The first three exercises
in the trail are free.

[Goal-Oriented Git]: https://gumroad.com/l/goal-oriented-git
[Mastering Git]: https://thoughtbot.com/upcase/mastering-git
[Upcase]: https://thoughtbot.com/upcase/join