Git补丁在同步不同分支的代码时应用较多，且比较灵活，比如修复了基线的一个bug，同步到各个版本的发布分支。本文介绍两种生成和应用补丁的方案。
1. diff/apply方案
此方案使用diff命令生成patch文件，后使用apply命令应用patch到分支，从而实现修改复刻。其大致流程如下：
# 生成补丁
git diff >
# 检查补丁
git apply --check
# 应用补丁
git apply
下面具体介绍操作方法：
1.1 diff生成patch
先看下git diff的帮助文档：
usage: git diff [<options>] [<commit>] [--] [<path>...]
or: git diff [<options>] --cached [<commit>] [--] [<path>...]
or: git diff [<options>] <commit> [<commit>...] <commit> [--] [<path>...]
or: git diff [<options>] <commit>...<commit>] [--] [<path>...]
or: git diff [<options>] <blob> <blob>]
or: git diff [<options>] --no-index [--] <path> <path>]
common diff options:
-z output diff-raw with lines terminated with NUL.
-p output patch format.
-u synonym for -p.
--patch-with-raw output both a patch and the diff-raw format.
--stat show diffstat instead of patch.
--numstat show numeric diffstat instead of patch.
--patch-with-stat output a patch and prepend its diffstat.
--name-only show only names of changed files.
--name-status show names and status of changed files.
--full-index show full object name on index lines.
--abbrev=<n> abbreviate object names in diff-tree header and diff-raw.
-R swap input file pairs.
-B detect complete rewrites.
-M detect renames.
-C detect copies.
--find-copies-harder try unchanged files as candidate for copy detection.
-l<n> limit rename attempts up to <n> paths.
-O<file> reorder diffs according to the <file>.
-S<string> find filepair whose only one side contains the string.
可见支持单个commit或多个commit生成patch，也支持对某个文件单独生成patch。这么多命令参数，该怎么去记住呢？实际上，diff本质上是对两个版本之间文件做数据比较得出差异，重点在于两个版本。下面我们逐一分析下不同命令参数下，这两个版本是指什么：
-
git diff
没有指定任何版本，那默认就是对lastCommit和working copy之间作比较。
这里就会出现两种情况：如果当前的
working copy已经commit过了，那么lastCommit就是目前working copy自身，所以diff不会输出任何内容；如果当前的working copy未commit，那么diff就会输出本次修改的内容。
-
git diff commitId
指定了一个commitId，那就是对commitId和working copy之间作比较。同样的，如果你的working copy已经commit过了，那么这个命令会等价于git diff commitId lastCommitId。 -
git diff commitId1 commitId2
指定了两个commitId（注意把时间早的commitId放在前面），这种情况就是对commitId1和commitId2之间作比较。
捋清楚这其中的关系，我们下面对日常开发中常见的场景进行介绍。
本地修改未commit
希望把修改的内容生成patch，可以如下操作：
git diff >
对于已经add但是未commit的修改：
git diff --cached >
本地修改已commit
希望把最近一次的修改生成patch：
# 注意：commitId为倒数第二个提交ID
git diff commitId >
1.2 apply应用patch
生成patch文件后，我们切换到希望应用patch的分支，然后按下面的步骤操作：
# 检查patch是否可以应用
git apply --check
# 打单个补丁
git apply
# 打多个补丁
git apply ../patch/*.patch
打完补丁后再add/commit进行提交。
看下apply命令的帮助文档：
usage: git apply [<options>] [<patch>...]
--exclude <path> 应用补丁时排除指定的目录/文件
--include <path> apply changes matching the given path
-p <num> remove <num> leading slashes from traditional diff paths
--no-add ignore additions made by the patch
--stat 仅展示补丁差异内容
--numstat show number of added and deleted lines in decimal notation
--summary 仅对补丁生成总结报告
--check 仅检查补丁是否可用
--index make sure the patch is applicable to the current index
-N, --intent-to-add mark new files with `git add --intent-to-add`
--cached apply a patch without touching the working tree
--unsafe-paths accept a patch that touches outside the working area
--apply also apply the patch (use with --stat/--summary/--check)
-3, --3way attempt three-way merge if a patch does not apply
--build-fake-ancestor <file> build a temporary index based on embedded index information
-z paths are separated with NUL character
-C <n> ensure at least <n> lines of context match
--whitespace <action> detect new or modified lines that have whitespace errors
--ignore-space-change ignore changes in whitespace when finding context
--ignore-whitespace ignore changes in whitespace when finding context
-R, --reverse apply the patch in reverse
--unidiff-zero don't expect at least one line of context
--reject leave the rejected hunks in corresponding *.rej files
--allow-overlap allow overlapping hunks
-v, --verbose be verbose
--inaccurate-eof tolerate incorrectly detected missing new-line at the end of file
--recount do not trust the line counts in the hunk headers
--directory <root> prepend <root> to all filenames
2. format-patch/am方案
这个方案是使用format-patch命令生成一系列patch文件，然后使用am命令批量应用patch。可以类比上一个方案进行理解，尤其是两个版本的概念是相同的。其大致流程如下：
# 生成patch
git format-patch -1
# 检查patch
git apply --check
# 应用patch
git am
为什么有了diff还要有format-patch呢？主要还是使用场景的不同：
- diff仅保留了文件重A状态变成B状态的差别，而不会保留commit记录消息等信息，而format-patch则是完整保留了每次提交的完成信息，这也解释了diff可以多个commit生成单个patch，而format-patch则是每个commit都生成一个patch文件。
- 两者是成对使用的，即
git apply使用的补丁必须是git diff生成的；git am的补丁必须是git format-patch生成的。当然补丁检查都是用git apply --check/--stat。
2.1 format-patch生成patch
format-patch命令是对指定版本范围内每次commit的修改生成对应的patch文件。
举个列子，现有如下提交历史的Git仓库：
D:\git_ws\test1>git log --pretty=oneline
4f499fc07597dcb5c7bb337116998a3e3e1f9116 (HEAD -> master) add third line
76a90ee80c67f310f6b6dc4b797cceedfa310368 add second line
ff53dd9d346dd3ab0013c0983160351d49a25024 Add
我们对它执行如下命令：
D:\git_ws\test1>git format-patch ff53dd
可见生成了以下两个patch：
- 76a90e ->
- 4f499f ->
文件名格式：序号-消息第一行.patch。另外值得说明的是，这个仓库其实本地已经修改了文件，但是没有commit，进一步验证了，format-patch仅对commit后的修改生成patch。这其实也比较好理解，没有提交的话，连commit msg都没有，patch文件名都没法定了。
看下format-patch命令的帮助文档：
usage: git format-patch [<options>] [<since> | <revision-range>]
-n, --numbered use [PATCH n/m] even with a single patch
-N, --no-numbered use [PATCH] even with multiple patches
-s, --signoff add Signed-off-by:
--stdout 指定输出位置，如所有patch输出到一个文件
--cover-letter generate a cover letter
--numbered-files 文件名只有编号，不包含提交信息
--suffix <sfx> 指定patch文件名后缀，默认'.patch'，比较常用的还有`.diff`
--start-number <n> start numbering patches at <n> instead of 1
-v, --reroll-count <n> mark the series as Nth re-roll
--rfc Use [RFC PATCH] instead of [PATCH]
--cover-from-description <cover-from-description-mode> generate parts of a cover letter based on a branch's description
--subject-prefix <prefix> Use [<prefix>] instead of [PATCH]
-o, --output-directory <dir> 指定patch的存放目录
-k, --keep-subject don't strip/add [PATCH]
--no-binary don't output binary diffs
--zero-commit output all-zero hash in From header
--ignore-if-in-upstream don't include a patch matching a commit upstream
-p, --no-stat show patch format instead of default (patch + stat)
当前分支所有超前master的提交
git format-patch -M master
某次提交以后的所有patch
git format-patch commitId
从根到指定提交的所有patch
git format-patch --root commitId
某两次提交之间的所有patch
git format-patch commitId1..commitId2
某次提交（含）之前的几次提交
# -n指patch数
git format-patch -n commitId
# 比如单次提交，生成commitId这次提交的patch
git format-patch -1 commitId
# 生成commitId前一次到commitId这两次修改的patch
git format-patch -2 commitId
2.2 am应用patch
git am可以一次合并一个文件，或者批量合并一个目录下所有的patch。在使用git am之前， 你要首先git am --abort一次，来放弃掉以前的am信息，这样才可以进行一次全新的am。不然会遇到这样的错误：
.git/rebase-apply still exists but mbox given.
具体操作如下：
- 打单个补丁
# 先检查patch文件：
git apply --stat
# 检查能否应用成功：
git apply --check
# 打补丁：使用-s或--signoff选项，可以commit信息中加入Signed-off-by信息
git am --signoff <
- 批量应用补丁
git am --abort
git am patch/*.patch
am命令的使用说明如下：
usage: git am [<options>] [(<mbox> | <Maildir>)...]
or: git am [<options>] (--continue | --skip | --abort)
-(<mbox> | <Maildir>)... 补丁路径
-i, --interactive run interactively
-3, --3way allow fall back on 3way merging if needed
-q, --quiet be quiet
-s, --signoff add a Signed-off-by line to the commit message
-u, --utf8 recode into utf8 (default)
-k, --keep pass -k flag to git-mailinfo
--keep-non-patch pass -b flag to git-mailinfo
-m, --message-id pass -m flag to git-mailinfo
--keep-cr pass --keep-cr flag to git-mailsplit for mbox format
--no-keep-cr do not pass --keep-cr flag to git-mailsplit independent of
-c, --scissors strip everything before a scissors line
--whitespace <action> pass it through git-apply
--ignore-space-change pass it through git-apply
--ignore-whitespace pass it through git-apply
--directory <root> pass it through git-apply
--exclude <path> pass it through git-apply
--include <path> pass it through git-apply
-C <n> pass it through git-apply
-p <num> pass it through git-apply
--patch-format <format> format the patch(es) are in
--reject pass it through git-apply
--resolvemsg ... override error message when patch failure occurs
--continue continue applying patches after resolving a conflict
-r, --resolved synonyms for --continue
--skip skip the current patch
--abort restore the original branch and abort the patching operation.
--quit abort the patching operation but keep HEAD where it is.
--show-current-patch[=(diff|raw)] show the patch being applied
--committer-date-is-author-date lie about committer date
--ignore-date use current timestamp for author date
--rerere-autoupdate update the index with reused conflict resolution if possible
-S, --gpg-sign[=<key-id>] GPG-sign commits
3. cherry-pick方案
比如需要将feature分支的修改同步到master分支上：
# 切换到master分支
git checkout master
# 选择和应用具体需要同步的提交
git cherry-pick <commitId>...
参考资料
- 如何使用git 生成patch 和打入patch