安装git

apt-get install git
yum install git

创建版本库

mkdir learngit
cd learngit
git init

git add <file>
git commit -m <message>

版本回退

git status   # 查看仓库当前状态
git diff readme.txt    # 查看修改内容

git log        # 查看提交历史，以便确定回退到哪个版本
git log --pretty=oneline
git reflog     # 查看命令历史，以便确定回到未来哪个版本 

git reset --hard HEAD^      # HEAD指当前版本，HEAD^指上一个版本
git reset --hard <commit_id>

工作区和暂存区

1. 工作区 Working Directory
2. 版本库 Repository
3. 暂存区 Stage

撤销修改

git checkout -- readme.txt      # 丢弃工作区的修改
# 1) 一种是文件修改后未被放到暂存区，撤销修改就回到和版本库相同的状态
# 2) 一种是文件被添加到暂存区后又做了修改，撤销修改就回到添加到暂存区后的状态
# 总之就是让文件回到最近一次 git add 或 git commit 时的状态
## git checkout -- file命令中的--很重要，没有--，就变成了“切换到另一个分支”的命令，我们在后面的分支管理中会再次遇到git checkout命令

git reset HEAD <file>     # 把暂存区的修改撤销(unstage)，重新放回工作区

删除文件

# 先添加一个文件testnew到Git并提交
[root@KARL learngit]# touch testnew
[root@KARL learngit]# git add testnew
[root@KARL learngit]# git commit -m "add testnew"
[master 10aa3df] add testnew
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 testnew

# 有如下两种情况：

## 1) 删除文件后发现是误删，可将误删文件恢复到最新版本
[root@KARL learngit]# rm -rf testnew
[root@KARL learngit]# ls
readme.txt
[root@KARL learngit]# git checkout -- testnew
[root@KARL learngit]# ls
readme.txt  testnew

## 2) 确实要从版本库中删除该文件
[root@KARL learngit]# rm -rf testnew
[root@KARL learngit]# ls
readme.txt
[root@KARL learngit]# git status
# On branch master
# Changes not staged for commit:
#   (use "git add/rm <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#       deleted:    testnew
#
no changes added to commit (use "git add" and/or "git commit -a")
[root@KARL learngit]# git rm testnew
rm 'testnew'
[root@KARL learngit]# git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       deleted:    testnew
#
[root@KARL learngit]# git commit -m "remove testnew"
[master 8f5bf72] remove testnew
 1 file changed, 0 insertions(+), 0 deletions(-)
 delete mode 100644 testnew
[root@KARL learngit]# git checkout -- testnew
error: pathspec 'testnew' did not match any file(s) known to git.

远程仓库

• Git是分布式版本控制系统，同一个Git仓库，可以分布到不同的机器上。怎么分布呢？最早，肯定只有一台机器有一个原始版本库，此后，别的机器可以“克隆”这个原始版本库，而且每台机器的版本库其实都是一样的，并没有主次之分。

添加远程库

1. 在本地执行 ssh-keygen -t rsa -b 4096，并将公钥上传至GitHub中的Deploy keys

"-b 4096" 不能省略，因为在GitHub上添加key时，必须大于2048位

2. 将本地库推送至远程库

git remote add origin git@github.com:Karl-luyi/learngit.git     # 关联远程库
git push -u origin master      # 第一次推送master分支的所有内容
git push origin master      # 推送最新修改

[root@KARL learngit]# git remote add origin git@github.com:karl-luyi/learngit.git
[root@KARL learngit]# git push -u origin master
The authenticity of host 'github.com (13.250.177.223)' can't be established.
RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
RSA key fingerprint is MD5:16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,13.250.177.223' (RSA) to the list of known hosts.
Counting objects: 18, done.
Compressing objects: 100% (13/13), done.
Writing objects: 100% (18/18), 1.50 KiB | 0 bytes/s, done.
Total 18 (delta 3), reused 0 (delta 0)
remote: Resolving deltas: 100% (3/3), done.
remote:
remote: Create a pull request for 'master' on GitHub by visiting:
remote:      https://github.com/Karl-luyi/learngit/pull/new/master
remote:
To git@github.com:karl-luyi/learngit.git
 * [new branch]      master -> master
Branch master set up to track remote branch master from origin.

从远程库克隆

1. 在GitHub上新建远程库
2. 从远程库克隆

[root@KARL learngit]# git clone git@github.com:Karl-luyi/gitskills.git
Cloning into 'gitskills'...
Warning: Permanently added the RSA host key for IP address '52.74.223.119' to the list of known hosts.
remote: Enumerating objects: 3, done.
remote: Counting objects: 100% (3/3), done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 0
Receiving objects: 100% (3/3), done.
[root@KARL learngit]# echo $?
0
[root@KARL learngit]# ls
gitskills  readme.txt
[root@KARL learngit]# cd gitskills/
[root@KARL gitskills]# ls
README.md
[root@KARL gitskills]# cat README.md
# gitskills
new remote repository

1. Git支持多种协议，包括https，但通过ssh支持的原生git协议速度最快。
2. 使用https除了速度慢以外，还有个最大的麻烦是每次推送都必须输入口令，但是在某些只开放http端口的公司内部就无法使用ssh协议而只能用https。

分支管理

[root@KARL gitskills]# git checkout -b dev       # 创建并切换，相当于2条命令：1) git branch dev  2) git checkout dev
Switched to a new branch 'dev'

[root@KARL gitskills]# git branch      # 查看当前分支
* dev
  master

[root@KARL gitskills]# git checkout master      # 切换至master分支
Switched to branch 'master'

[root@KARL gitskills]# git merge dev      # 将dev分支上合并到master分支上
Updating 13079c7..9f63516
Fast-forward
 readme.txt | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 readme.txt

[root@KARL gitskills]# git branch -d dev      # 删除dev分支
Deleted branch dev (was 9f63516).
[root@KARL gitskills]# git branch
* master

[root@KARL gitskills]# git remote -v      # 查看远程库信息
origin  git@github.com:Karl-luyi/gitskills.git (fetch)
origin  git@github.com:Karl-luyi/gitskills.git (push)

总结
查看分支：git branch
创建分支：git branch <name>
切换分支：git checkout <name>
创建+切换分支：git checkout -b <name>
合并某分支到当前分支：git merge <name>
删除分支：git branch -d <name>