git fetch & git pull

解析.git文件夹

进入正题之前，我们先来看看.git文件夹

1.config配置文件

[core]

repositoryformatversion = 0
filemode = true
bare = false
logallrefupdates = true
sharedRepository = group

[remote "origin"]

url = https://xxx/xxx/xxx.git
fetch = +refs/heads/*:refs/remotes/origin/*

[branch "master"]

remote = origin
merge = refs/heads/master

配置文件可以看出
(1).指定本地master分支对应名为"origin"的远程库
(2).名为"origin"的远程库的URL（位置）为：https://xxx/xxx/xxx.git

2.HEAD文件

ref: refs/heads/issue178

这表明当前分支是issue178，查看当前分支最新<commit>需查看文件 .git/refs/heads/issue178
终端用命令git branch可查看当前所在分支。查看当前分支最新<commit>（即HEAD指向）用命令git log

3.refs文件夹

.git/refs/heads文件夹：保存着本地各个分支的信息
.git/refs/remotes 文件夹：其中每一个文件夹代表一个远程库名称（如：origin）

4.logs文件夹

保存的是.git/refs文件夹下相应文件的变更记录，也就是各个分支变更记录

git fetch & git pull

1.git fetch：从远程获取最新版本到本地，不会自动merge

git checkout issue178
git fetch origin issue178
git log -p issue178..origin/issue178
git merge origin/issue178

解析:
(1).切换到issue178分支
(2).从远程的origin的issue178主分支下载最新的版本到origin/issue178分支上
(3).比较本地的issue178分支和origin/issue178分支的差别
(4).将origin/issue178分支合并到issue178

上述的另一种清晰的实现：

git checkout issue178
git fetch origin issue178:test
git diff test
git merge test

解析:
(1).切换到issue178分支
(2).从远程的origin的issue178主分支下载最新的版本到本地的test分支
(3).比较本地的issue178分支和test分支的差别
(4).将test分支合并到issue178

2.git pull：相当于是从远程获取最新版本并merge到本地

git checkout issue178
git pull origin issue178

解析:
等同于上述命令。即git pull相当于git fetch 和 git merge

3.Example

(1) git fetch

git fetch origin issue178:issue178

issue178最新<commit>id：c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1
origin issue178最新<commit>id：fea9f020b60e9db120395c7ed9c57bd12cd7c085

执行前：
.git/refs/heads/issue178文件内容

c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1

注：也可查看.git/logs/refs/heads/issue178

.git/refs/remotes/origin/issue178文件内容

c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1

注：也可查看.git/logs/refs/remotes/origin/issue178

执行后：
.git/refs/heads/issue178文件不变
.git/logs/refs/heads/issue178文件不变

.git/refs/remotes/origin/issue178文件内容变化

fea9f020b60e9db120395c7ed9c57bd12cd7c085

.git/logs/refs/remotes/origin/issue178文件内容变化

(2) git pull

git pull origin issue178:issue178

issue178最新<commit>id：c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1
origin issue178最新<commit>id：fea9f020b60e9db120395c7ed9c57bd12cd7c085

执行前：
.git/refs/heads/issue178文件内容

c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1

注：也可查看.git/logs/refs/heads/issue178

.git/refs/remotes/origin/issue178文件内容

c75abf94ced40ce49e4807fc0b0fb4b2a3dad7f1

注：也可查看.git/logs/refs/remotes/origin/issue178

执行后：
.git/refs/heads/issue178文件内容变化

fea9f020b60e9db120395c7ed9c57bd12cd7c085

.git/logs/refs/heads/issue178文件内容变化

.git/refs/remotes/origin/issue178文件内容不变
.git/logs/refs/remotes/origin/issue178文件内容不变

4.图示