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git-format-patch(1)
===================

NAME
----
git-format-patch - Prepare patches for e-mail submission


SYNOPSIS
--------
[verse]
'git format-patch' [-k] [(-o|--output-directory) <dir> | --stdout]
                   [--no-thread | --thread[=<style>]]
                   [(--attach|--inline)[=<boundary>] | --no-attach]
                   [-s | --signoff]
                   [--signature=<signature> | --no-signature]
                   [--signature-file=<file>]
                   [-n | --numbered | -N | --no-numbered]
                   [--start-number <n>] [--numbered-files]
                   [--in-reply-to=<message-id>] [--suffix=.<sfx>]
                   [--ignore-if-in-upstream] [--always]
                   [--cover-from-description=<mode>]
                   [--rfc[=<rfc>]] [--subject-prefix=<subject-prefix>]
                   [(--reroll-count|-v) <n>]
                   [--to=<email>] [--cc=<email>]
                   [--[no-]cover-letter] [--quiet]
                   [--[no-]encode-email-headers]
                   [--no-notes | --notes[=<ref>]]
                   [--interdiff=<previous>]
                   [--range-diff=<previous> [--creation-factor=<percent>]]
                   [--filename-max-length=<n>]
                   [--progress]
                   [<common-diff-options>]
                   [ <since> | <revision-range> ]

DESCRIPTION
-----------

Prepare each non-merge commit with its "patch" in
one "message" per commit, formatted to resemble a UNIX mailbox.
The output of this command is convenient for e-mail submission or
for use with 'git am'.

A "message" generated by the command consists of three parts:

* A brief metadata header that begins with `From <commit>`
  with a fixed `Mon Sep 17 00:00:00 2001` datestamp to help programs
  like "file(1)" to recognize that the file is an output from this
  command, fields that record the author identity, the author date,
  and the title of the change (taken from the first paragraph of the
  commit log message).

* The second and subsequent paragraphs of the commit log message.

* The "patch", which is the "diff -p --stat" output (see
  linkgit:git-diff[1]) between the commit and its parent.

The log message and the patch are separated by a line with a
three-dash line.

There are two ways to specify which commits to operate on.

1. A single commit, <since>, specifies that the commits leading
   to the tip of the current branch that are not in the history
   that leads to the <since> to be output.

2. Generic <revision-range> expression (see "SPECIFYING
   REVISIONS" section in linkgit:gitrevisions[7]) means the
   commits in the specified range.

The first rule takes precedence in the case of a single <commit>.  To
apply the second rule, i.e., format everything since the beginning of
history up until <commit>, use the `--root` option: `git format-patch
--root <commit>`.  If you want to format only <commit> itself, you
can do this with `git format-patch -1 <commit>`.

By default, each output file is numbered sequentially from 1, and uses the
first line of the commit message (massaged for pathname safety) as
the filename. With the `--numbered-files` option, the output file names
will only be numbers, without the first line of the commit appended.
The names of the output files are printed to standard
output, unless the `--stdout` option is specified.

If `-o` is specified, output files are created in <dir>.  Otherwise
they are created in the current working directory. The default path
can be set with the `format.outputDirectory` configuration option.
The `-o` option takes precedence over `format.outputDirectory`.
To store patches in the current working directory even when
`format.outputDirectory` points elsewhere, use `-o .`. All directory
components will be created.

By default, the subject of a single patch is "[PATCH] " followed by
the concatenation of lines from the commit message up to the first blank
line (see the DISCUSSION section of linkgit:git-commit[1]).

When multiple patches are output, the subject prefix will instead be
"[PATCH n/m] ".  To force 1/1 to be added for a single patch, use `-n`.
To omit patch numbers from the subject, use `-N`.

If given `--thread`, `git-format-patch` will generate `In-Reply-To` and
`References` headers to make the second and subsequent patch mails appear
as replies to the first mail; this also generates a `Message-ID` header to
reference.

OPTIONS
-------
:git-format-patch: 1
include::diff-options.txt[]

-<n>::
        Prepare patches from the topmost <n> commits.

-o <dir>::
--output-directory <dir>::
        Use <dir> to store the resulting files, instead of the
        current working directory.

-n::
--numbered::
        Name output in '[PATCH n/m]' format, even with a single patch.

-N::
--no-numbered::
        Name output in '[PATCH]' format.

--start-number <n>::
        Start numbering the patches at <n> instead of 1.

--numbered-files::
        Output file names will be a simple number sequence
        without the default first line of the commit appended.

-k::
--keep-subject::
        Do not strip/add '[PATCH]' from the first line of the
        commit log message.

-s::
--signoff::
        Add a `Signed-off-by` trailer to the commit message, using
        the committer identity of yourself.
        See the signoff option in linkgit:git-commit[1] for more information.

--stdout::
        Print all commits to the standard output in mbox format,
        instead of creating a file for each one.

--attach[=<boundary>]::
        Create multipart/mixed attachment, the first part of
        which is the commit message and the patch itself in the
        second part, with `Content-Disposition: attachment`.

--no-attach::
        Disable the creation of an attachment, overriding the
        configuration setting.

--inline[=<boundary>]::
        Create multipart/mixed attachment, the first part of
        which is the commit message and the patch itself in the
        second part, with `Content-Disposition: inline`.

--thread[=<style>]::
--no-thread::
        Controls addition of `In-Reply-To` and `References` headers to
        make the second and subsequent mails appear as replies to the
        first.  Also controls generation of the `Message-ID` header to
        reference.
+
The optional <style> argument can be either `shallow` or `deep`.
'shallow' threading makes every mail a reply to the head of the
series, where the head is chosen from the cover letter, the
`--in-reply-to`, and the first patch mail, in this order.  'deep'
threading makes every mail a reply to the previous one.
+
The default is `--no-thread`, unless the `format.thread` configuration
is set.  `--thread` without an argument is equivalent to `--thread=shallow`.
+
Beware that the default for 'git send-email' is to thread emails
itself.  If you want `git format-patch` to take care of threading, you
will want to ensure that threading is disabled for `git send-email`.

--in-reply-to=<message-id>::
        Make the first mail (or all the mails with `--no-thread`) appear as a
        reply to the given <message-id>, which avoids breaking threads to
        provide a new patch series.

--ignore-if-in-upstream::
        Do not include a patch that matches a commit in
        <until>..<since>.  This will examine all patches reachable
        from <since> but not from <until> and compare them with the
        patches being generated, and any patch that matches is
        ignored.

--always::
        Include patches for commits that do not introduce any change,
        which are omitted by default.

--cover-from-description=<mode>::
        Controls which parts of the cover letter will be automatically
        populated using the branch's description.
+
If `<mode>` is `message` or `default`, the cover letter subject will be
populated with placeholder text. The body of the cover letter will be
populated with the branch's description. This is the default mode when
no configuration nor command line option is specified.
+
If `<mode>` is `subject`, the first paragraph of the branch description will
populate the cover letter subject. The remainder of the description will
populate the body of the cover letter.
+
If `<mode>` is `auto`, if the first paragraph of the branch description
is greater than 100 bytes, then the mode will be `message`, otherwise
`subject` will be used.
+
If `<mode>` is `none`, both the cover letter subject and body will be
populated with placeholder text.

--description-file=<file>::
        Use the contents of <file> instead of the branch's description
        for generating the cover letter.

--subject-prefix=<subject-prefix>::
        Instead of the standard '[PATCH]' prefix in the subject
        line, instead use '[<subject-prefix>]'. This can be used
        to name a patch series, and can be combined with the
        `--numbered` option.
+
The configuration variable `format.subjectPrefix` may also be used
to configure a subject prefix to apply to a given repository for
all patches. This is often useful on mailing lists which receive
patches for several repositories and can be used to disambiguate
the patches (with a value of e.g. "PATCH my-project").

--filename-max-length=<n>::
        Instead of the standard 64 bytes, chomp the generated output
        filenames at around '<n>' bytes (too short a value will be
        silently raised to a reasonable length).  Defaults to the
        value of the `format.filenameMaxLength` configuration
        variable, or 64 if unconfigured.

--rfc[=<rfc>]::
        Prepends the string _<rfc>_ (defaults to "RFC") to
        the subject prefix.  As the subject prefix defaults to
        "PATCH", you'll get "RFC PATCH" by default.
+
RFC means "Request For Comments"; use this when sending
an experimental patch for discussion rather than application.
"--rfc=WIP" may also be a useful way to indicate that a patch
is not complete yet ("WIP" stands for "Work In Progress").
+
If the convention of the receiving community for a particular extra
string is to have it _after_ the subject prefix, the string _<rfc>_
can be prefixed with a dash ("`-`") to signal that the the rest of
the _<rfc>_ string should be appended to the subject prefix instead,
e.g., `--rfc='-(WIP)'` results in "PATCH (WIP)".

-v <n>::
--reroll-count=<n>::
        Mark the series as the <n>-th iteration of the topic. The
        output filenames have `v<n>` prepended to them, and the
        subject prefix ("PATCH" by default, but configurable via the
        `--subject-prefix` option) has ` v<n>` appended to it.  E.g.
        `--reroll-count=4` may produce `v4-0001-add-makefile.patch`
        file that has "Subject: [PATCH v4 1/20] Add makefile" in it.
        `<n>` does not have to be an integer (e.g. "--reroll-count=4.4",
        or "--reroll-count=4rev2" are allowed), but the downside of
        using such a reroll-count is that the range-diff/interdiff
        with the previous version does not state exactly which
        version the new iteration is compared against.

--to=<email>::
        Add a `To:` header to the email headers. This is in addition
        to any configured headers, and may be used multiple times.
        The negated form `--no-to` discards all `To:` headers added so
        far (from config or command line).

--cc=<email>::
        Add a `Cc:` header to the email headers. This is in addition
        to any configured headers, and may be used multiple times.
        The negated form `--no-cc` discards all `Cc:` headers added so
        far (from config or command line).

--from::
--from=<ident>::
        Use `ident` in the `From:` header of each commit email. If the
        author ident of the commit is not textually identical to the
        provided `ident`, place a `From:` header in the body of the
        message with the original author. If no `ident` is given, use
        the committer ident.
+
Note that this option is only useful if you are actually sending the
emails and want to identify yourself as the sender, but retain the
original author (and `git am` will correctly pick up the in-body
header). Note also that `git send-email` already handles this
transformation for you, and this option should not be used if you are
feeding the result to `git send-email`.

--[no-]force-in-body-from::
        With the e-mail sender specified via the `--from` option, by
        default, an in-body "From:" to identify the real author of
        the commit is added at the top of the commit log message if
        the sender is different from the author.  With this option,
        the in-body "From:" is added even when the sender and the
        author have the same name and address, which may help if the
        mailing list software mangles the sender's identity.
        Defaults to the value of the `format.forceInBodyFrom`
        configuration variable.

--add-header=<header>::
        Add an arbitrary header to the email headers.  This is in addition
        to any configured headers, and may be used multiple times.
        For example, `--add-header="Organization: git-foo"`.
        The negated form `--no-add-header` discards *all* (`To:`,
        `Cc:`, and custom) headers added so far from config or command
        line.

--[no-]cover-letter::
        In addition to the patches, generate a cover letter file
        containing the branch description, shortlog and the overall diffstat.  You can
        fill in a description in the file before sending it out.

--encode-email-headers::
--no-encode-email-headers::
        Encode email headers that have non-ASCII characters with
        "Q-encoding" (described in RFC 2047), instead of outputting the
        headers verbatim. Defaults to the value of the
        `format.encodeEmailHeaders` configuration variable.

--interdiff=<previous>::
        As a reviewer aid, insert an interdiff into the cover letter,
        or as commentary of the lone patch of a 1-patch series, showing
        the differences between the previous version of the patch series and
        the series currently being formatted. `previous` is a single revision
        naming the tip of the previous series which shares a common base with
        the series being formatted (for example `git format-patch
        --cover-letter --interdiff=feature/v1 -3 feature/v2`).

--range-diff=<previous>::
        As a reviewer aid, insert a range-diff (see linkgit:git-range-diff[1])
        into the cover letter, or as commentary of the lone patch of a
        1-patch series, showing the differences between the previous
        version of the patch series and the series currently being formatted.
        `previous` can be a single revision naming the tip of the previous
        series if it shares a common base with the series being formatted (for
        example `git format-patch --cover-letter --range-diff=feature/v1 -3
        feature/v2`), or a revision range if the two versions of the series are
        disjoint (for example `git format-patch --cover-letter
        --range-diff=feature/v1~3..feature/v1 -3 feature/v2`).
+
Note that diff options passed to the command affect how the primary
product of `format-patch` is generated, and they are not passed to
the underlying `range-diff` machinery used to generate the cover-letter
material (this may change in the future).

--creation-factor=<percent>::
        Used with `--range-diff`, tweak the heuristic which matches up commits
        between the previous and current series of patches by adjusting the
        creation/deletion cost fudge factor. See linkgit:git-range-diff[1])
        for details.
+
Defaults to 999 (the linkgit:git-range-diff[1] uses 60), as the use
case is to show comparison with an older iteration of the same
topic and the tool should find more correspondence between the two
sets of patches.

--notes[=<ref>]::
--no-notes::
        Append the notes (see linkgit:git-notes[1]) for the commit
        after the three-dash line.
+
The expected use case of this is to write supporting explanation for
the commit that does not belong to the commit log message proper,
and include it with the patch submission. While one can simply write
these explanations after `format-patch` has run but before sending,
keeping them as Git notes allows them to be maintained between versions
of the patch series (but see the discussion of the `notes.rewrite`
configuration options in linkgit:git-notes[1] to use this workflow).
+
The default is `--no-notes`, unless the `format.notes` configuration is
set.

--[no-]signature=<signature>::
        Add a signature to each message produced. Per RFC 3676 the signature
        is separated from the body by a line with '-- ' on it. If the
        signature option is omitted the signature defaults to the Git version
        number.

--signature-file=<file>::
        Works just like --signature except the signature is read from a file.

--suffix=.<sfx>::
        Instead of using `.patch` as the suffix for generated
        filenames, use specified suffix.  A common alternative is
        `--suffix=.txt`.  Leaving this empty will remove the `.patch`
        suffix.
+
Note that the leading character does not have to be a dot; for example,
you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.

-q::
--quiet::
        Do not print the names of the generated files to standard output.

--no-binary::
        Do not output contents of changes in binary files, instead
        display a notice that those files changed.  Patches generated
        using this option cannot be applied properly, but they are
        still useful for code review.

--zero-commit::
  Output an all-zero hash in each patch's From header instead
  of the hash of the commit.

--[no-]base[=<commit>]::
        Record the base tree information to identify the state the
        patch series applies to.  See the BASE TREE INFORMATION section
        below for details. If <commit> is "auto", a base commit is
        automatically chosen. The `--no-base` option overrides a
        `format.useAutoBase` configuration.

--root::
        Treat the revision argument as a <revision-range>, even if it
        is just a single commit (that would normally be treated as a
        <since>).  Note that root commits included in the specified
        range are always formatted as creation patches, independently
        of this flag.

--progress::
        Show progress reports on stderr as patches are generated.

CONFIGURATION
-------------
You can specify extra mail header lines to be added to each message,
defaults for the subject prefix and file suffix, number patches when
outputting more than one patch, add "To:" or "Cc:" headers, configure
attachments, change the patch output directory, and sign off patches
with configuration variables.

------------
[format]
        headers = "Organization: git-foo\n"
        subjectPrefix = CHANGE
        suffix = .txt
        numbered = auto
        to = <email>
        cc = <email>
        attach [ = mime-boundary-string ]
        signOff = true
        outputDirectory = <directory>
        coverLetter = auto
        coverFromDescription = auto
------------


DISCUSSION
----------

The patch produced by 'git format-patch' is in UNIX mailbox format,
with a fixed "magic" time stamp to indicate that the file is output
from format-patch rather than a real mailbox, like so:

------------
From 8f72bad1baf19a53459661343e21d6491c3908d3 Mon Sep 17 00:00:00 2001
From: Tony Luck <tony.luck@intel.com>
Date: Tue, 13 Jul 2010 11:42:54 -0700
Subject: [PATCH] =?UTF-8?q?[IA64]=20Put=20ia64=20config=20files=20on=20the=20?=
 =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig=20diet?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

arch/arm config files were slimmed down using a python script
(See commit c2330e286f68f1c408b4aa6515ba49d57f05beae comment)

Do the same for ia64 so we can have sleek & trim looking
...
------------

Typically it will be placed in a MUA's drafts folder, edited to add
timely commentary that should not go in the changelog after the three
dashes, and then sent as a message whose body, in our example, starts
with "arch/arm config files were...".  On the receiving end, readers
can save interesting patches in a UNIX mailbox and apply them with
linkgit:git-am[1].

When a patch is part of an ongoing discussion, the patch generated by
'git format-patch' can be tweaked to take advantage of the 'git am
--scissors' feature.  After your response to the discussion comes a
line that consists solely of "`-- >8 --`" (scissors and perforation),
followed by the patch with unnecessary header fields removed:

------------
...
> So we should do such-and-such.

Makes sense to me.  How about this patch?

-- >8 --
Subject: [IA64] Put ia64 config files on the Uwe Kleine-König diet

arch/arm config files were slimmed down using a python script
...
------------

When sending a patch this way, most often you are sending your own
patch, so in addition to the "`From $SHA1 $magic_timestamp`" marker you
should omit `From:` and `Date:` lines from the patch file.  The patch
title is likely to be different from the subject of the discussion the
patch is in response to, so it is likely that you would want to keep
the Subject: line, like the example above.

Checking for patch corruption
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Many mailers if not set up properly will corrupt whitespace.  Here are
two common types of corruption:

* Empty context lines that do not have _any_ whitespace.

* Non-empty context lines that have one extra whitespace at the
  beginning.

One way to test if your MUA is set up correctly is:

* Send the patch to yourself, exactly the way you would, except
  with To: and Cc: lines that do not contain the list and
  maintainer address.

* Save that patch to a file in UNIX mailbox format.  Call it a.patch,
  say.

* Apply it:

    $ git fetch <project> master:test-apply
    $ git switch test-apply
    $ git restore --source=HEAD --staged --worktree :/
    $ git am a.patch

If it does not apply correctly, there can be various reasons.

* The patch itself does not apply cleanly.  That is _bad_ but
  does not have much to do with your MUA.  You might want to rebase
  the patch with linkgit:git-rebase[1] before regenerating it in
  this case.

* The MUA corrupted your patch; "am" would complain that
  the patch does not apply.  Look in the .git/rebase-apply/ subdirectory and
  see what 'patch' file contains and check for the common
  corruption patterns mentioned above.

* While at it, check the 'info' and 'final-commit' files as well.
  If what is in 'final-commit' is not exactly what you would want to
  see in the commit log message, it is very likely that the
  receiver would end up hand editing the log message when applying
  your patch.  Things like "Hi, this is my first patch.\n" in the
  patch e-mail should come after the three-dash line that signals
  the end of the commit message.

MUA-SPECIFIC HINTS
------------------
Here are some hints on how to successfully submit patches inline using
various mailers.

GMail
~~~~~
GMail does not have any way to turn off line wrapping in the web
interface, so it will mangle any emails that you send.  You can however
use "git send-email" and send your patches through the GMail SMTP server, or
use any IMAP email client to connect to the google IMAP server and forward
the emails through that.

For hints on using 'git send-email' to send your patches through the
GMail SMTP server, see the EXAMPLE section of linkgit:git-send-email[1].

For hints on submission using the IMAP interface, see the EXAMPLE
section of linkgit:git-imap-send[1].

Thunderbird
~~~~~~~~~~~
By default, Thunderbird will both wrap emails as well as flag
them as being 'format=flowed', both of which will make the
resulting email unusable by Git.

There are three different approaches: use an add-on to turn off line wraps,
configure Thunderbird to not mangle patches, or use
an external editor to keep Thunderbird from mangling the patches.

Approach #1 (add-on)
^^^^^^^^^^^^^^^^^^^^

Install the Toggle Word Wrap add-on that is available from
https://addons.mozilla.org/thunderbird/addon/toggle-word-wrap/
It adds a menu entry "Enable Word Wrap" in the composer's "Options" menu
that you can tick off. Now you can compose the message as you otherwise do
(cut + paste, 'git format-patch' | 'git imap-send', etc), but you have to
insert line breaks manually in any text that you type.

Approach #2 (configuration)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Three steps:

1. Configure your mail server composition as plain text:
   Edit...Account Settings...Composition & Addressing,
   uncheck "Compose Messages in HTML".

2. Configure your general composition window to not wrap.
+
In Thunderbird 2:
Edit..Preferences..Composition, wrap plain text messages at 0
+
In Thunderbird 3:
Edit..Preferences..Advanced..Config Editor.  Search for
"mail.wrap_long_lines".
Toggle it to make sure it is set to `false`. Also, search for
"mailnews.wraplength" and set the value to 0.

3. Disable the use of format=flowed:
   Edit..Preferences..Advanced..Config Editor.  Search for
   "mailnews.send_plaintext_flowed".
   Toggle it to make sure it is set to `false`.

After that is done, you should be able to compose email as you
otherwise would (cut + paste, 'git format-patch' | 'git imap-send', etc),
and the patches will not be mangled.

Approach #3 (external editor)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The following Thunderbird extensions are needed:
AboutConfig from https://mjg.github.io/AboutConfig/ and
External Editor from https://globs.org/articles.php?lng=en&pg=8

1. Prepare the patch as a text file using your method of choice.

2. Before opening a compose window, use Edit->Account Settings to
   uncheck the "Compose messages in HTML format" setting in the
   "Composition & Addressing" panel of the account to be used to
   send the patch.

3. In the main Thunderbird window, 'before' you open the compose
   window for the patch, use Tools->about:config to set the
   following to the indicated values:
+
----------
        mailnews.send_plaintext_flowed  => false
        mailnews.wraplength             => 0
----------

4. Open a compose window and click the external editor icon.

5. In the external editor window, read in the patch file and exit
   the editor normally.

Side note: it may be possible to do step 2 with
about:config and the following settings but no one's tried yet.

----------
        mail.html_compose                       => false
        mail.identity.default.compose_html      => false
        mail.identity.id?.compose_html          => false
----------

There is a script in contrib/thunderbird-patch-inline which can help
you include patches with Thunderbird in an easy way. To use it, do the
steps above and then use the script as the external editor.

KMail
~~~~~
This should help you to submit patches inline using KMail.

1. Prepare the patch as a text file.

2. Click on New Mail.

3. Go under "Options" in the Composer window and be sure that
   "Word wrap" is not set.

4. Use Message -> Insert file... and insert the patch.

5. Back in the compose window: add whatever other text you wish to the
   message, complete the addressing and subject fields, and press send.

BASE TREE INFORMATION
---------------------

The base tree information block is used for maintainers or third party
testers to know the exact state the patch series applies to. It consists
of the 'base commit', which is a well-known commit that is part of the
stable part of the project history everybody else works off of, and zero
or more 'prerequisite patches', which are well-known patches in flight
that is not yet part of the 'base commit' that need to be applied on top
of 'base commit' in topological order before the patches can be applied.

The 'base commit' is shown as "base-commit: " followed by the 40-hex of
the commit object name.  A 'prerequisite patch' is shown as
"prerequisite-patch-id: " followed by the 40-hex 'patch id', which can
be obtained by passing the patch through the `git patch-id --stable`
command.

Imagine that on top of the public commit P, you applied well-known
patches X, Y and Z from somebody else, and then built your three-patch
series A, B, C, the history would be like:

................................................
---P---X---Y---Z---A---B---C
................................................

With `git format-patch --base=P -3 C` (or variants thereof, e.g. with
`--cover-letter` or using `Z..C` instead of `-3 C` to specify the
range), the base tree information block is shown at the end of the
first message the command outputs (either the first patch, or the
cover letter), like this:

------------
base-commit: P
prerequisite-patch-id: X
prerequisite-patch-id: Y
prerequisite-patch-id: Z
------------

For non-linear topology, such as

................................................
---P---X---A---M---C
    \         /
     Y---Z---B
................................................

You can also use `git format-patch --base=P -3 C` to generate patches
for A, B and C, and the identifiers for P, X, Y, Z are appended at the
end of the first message.

If set `--base=auto` in cmdline, it will automatically compute
the base commit as the merge base of tip commit of the remote-tracking
branch and revision-range specified in cmdline.
For a local branch, you need to make it to track a remote branch by `git branch
--set-upstream-to` before using this option.

EXAMPLES
--------

* Extract commits between revisions R1 and R2, and apply them on top of
  the current branch using 'git am' to cherry-pick them:
+
------------
$ git format-patch -k --stdout R1..R2 | git am -3 -k
------------

* Extract all commits which are in the current branch but not in the
  origin branch:
+
------------
$ git format-patch origin
------------
+
For each commit a separate file is created in the current directory.

* Extract all commits that lead to 'origin' since the inception of the
  project:
+
------------
$ git format-patch --root origin
------------

* The same as the previous one:
+
------------
$ git format-patch -M -B origin
------------
+
Additionally, it detects and handles renames and complete rewrites
intelligently to produce a renaming patch.  A renaming patch reduces
the amount of text output, and generally makes it easier to review.
Note that non-Git "patch" programs won't understand renaming patches, so
use it only when you know the recipient uses Git to apply your patch.

* Extract three topmost commits from the current branch and format them
  as e-mailable patches:
+
------------
$ git format-patch -3
------------

CAVEATS
-------

Note that `format-patch` will omit merge commits from the output, even
if they are part of the requested range. A simple "patch" does not
include enough information for the receiving end to reproduce the same
merge commit.

SEE ALSO
--------
linkgit:git-am[1], linkgit:git-send-email[1]

GIT
---
Part of the linkgit:git[1] suite