合并commit的做法一般用在pull request的时候，把开发同一功能时的所有琐碎的commit合并到一个（假装自己的代码是高质量代码（手动滑稽））。主要使用的命令是git rebase 或者git reset，这两个命令的区别可以看这里，一般推荐用git rebase，因为commit的历史能保存下来。

1. git rebase

首先用git log查看commit历史确定需要操作的commit，比如：

commit 0bca654809387dc226cfc4ff872f65601809f485
Author: CasiaFan <fanzongshaoxing@gmail.com>
Date:   Wed Aug 16 13:13:12 2017 +0800fix typocommit b5bf9998e40dc165d7e3055bae47172de11225d4
Author: CasiaFan <fanzongshaoxing@gmail.com>
Date:   Wed Aug 16 10:02:30 2017 +0800add random vertical flip during image preprocessingcommit 70a4958184106b9ce848da34be34bdf0dbf36450
Author: CasiaFan <fanzongshaoxing@gmail.com>
Date:   Wed Aug 16 09:58:55 2017 +0800step by step runningcommit d68608c2dbd41a1b89363f4b743bc5464b6749be
Author: CasiaFan <fanzongshaoxing@gmail.com>
Date:   Mon Aug 14 15:52:47 2017 +0800modify description

如果需要操作最近4个commit:

git rebase -i HEAD~4   # 操作对象为从倒数第4个commit开始到当前的commit
# git rebase -i d68608c2dbd41a1b89363f4b743bc5464b6749be  # 倒数第4个commit 的id

然后会跳出编辑页面像这样：

pick d68608c modify description
pick 70a4958 step by step running
pick b5bf999 add random vertical flip during image preprocessing
pick 0bca654 fix typo# Rebase 529bf46..0bca654 onto 529bf46 (4 command(s))
#
# Commands:
# p, pick = use commit
# r, reword = use commit, but edit the commit message
# e, edit = use commit, but stop for amending
# s, squash = use commit, but meld into previous commit
# f, fixup = like "squash", but discard this commit's log message
# x, exec = run command (the rest of the line) using shell
# d, drop = remove commit
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
# However, if you remove everything, the rebase will be aborted.
#
# Note that empty commits are commented out

把需要保留的commit之前保留pick，需要合并的前面改成squash，编辑保存退出以后输入新的commit message，最后保存退出。

# This is a combination of 6 commits.
add random vertical flip for image preprocessing  # 合并后的commit
# The first commit's message is:
test
# This is the 2nd commit message:object detection api usage step# This is the 3rd commit message:modify description# This is the 4th commit message:step by step running# This is the 5th commit message:add random vertical flip during image preprocessing# This is the 6th commit message:fix typo

这个时候再git log的日志如下：

commit 7f774d88eb6884c97c8b3c05a9268afa581d5b57
Author: Unknown <fanzongshaoxing@gmail.com>
Date:   Mon Aug 14 15:45:29 2017 +0800add random vertical flip for image preprocessingtestobject detection api usage stepmodify descriptionstep by step runningadd random vertical flip during image preprocessingfix typo

如果修改了一半不想合并了就用git rebase --abort删除。

git reset

git reset --soft "HEAD~4"
git commit --amend

或者

git reset --hard HEAD~4  # 将branch状态切到到4个commit之前
git merge --squash HEAD@{1}  # 将当前commit（此时为倒数第四个）之后的commit都合并
git commit # commit squashed changes

参考

https://stackoverflow.com/questions/5189560/squash-my-last-x-commits-together-using-git
https://stackoverflow.com/questions/2563632/how-can-i-merge-two-commits-into-one
http://zerodie.github.io/blog/2012/01/19/git-rebase-i/