git init

Create an empty Git repository or reinitialize an existing one 也即是向 working directory 里添加 .git 文件夹

.git/
├── branches # git 分支
├── config   # git 配置
├── description
├── HEAD     # HEAD 指针, 指向当前分支最新的 commit
├── hooks
│   ├── applypatch-msg.sample
│   ├── commit-msg.sample
│   ├── fsmonitor-watchman.sample
│   ├── post-update.sample
│   ├── pre-applypatch.sample
│   ├── pre-commit.sample
│   ├── prepare-commit-msg.sample
│   ├── pre-push.sample
│   ├── pre-rebase.sample
│   ├── pre-receive.sample
│   └── update.sample
├── info
│   └── exclude
├── objects   # 存放不同种类的 git 对象，实现版本管理的关键 
│   ├── info
│   └── pack
└── refs
    ├── heads 
    └── tags  # git 标签

第一次 git add | git commit

git add

Add file contents to the index 添加文件内容到 index 区

  1. 添加两个文件 file1 和 file2, 文件内容分别是 111 和 222

  2. git add file_name

git add file1
  1. tree .git/objects 查看添加的 git object
.git/objects/
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── info
└── pack

对 file1 文件内容也就是 111 和一些其他的信息做 SHA-1 运算得出 58c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c 这个 40 位 16 进制的值.

  1. git cat-file 查看 objects 相关信息 查看 object 类型
git cat-file -t 58c9bd
blob

查看 object 大小

git cat-file -s 58c9bd
4

查看 object 内容

git cat-file -p 58c9bd
111
  1. 对文件内容为 222 的 file2 进行步骤 2 ~ 4.

查看 .git/objects 如下:

.git/objects/
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c # file1:blob
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c # file2:blob
├── info
└── pack

git commit

Stores the current contents of the index in a new commit along with a log message from the user describing the changes. A commit in a git repository records a snapshot of all the files in your directory.

执行 git commit -m “add file1 and file2”

查看 .git/objects 的变化

tree .git/objects
.git/objects/
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c # file1:blob
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5 # 1:commit
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c # file2:blob
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0 # 1:tree
├── info
└── pack

查看 HEAD

root@aliyun:~/blog# cat .git/HEAD
ref: refs/heads/master # 目前在 master 分支上
root@aliyun:~/blog# cat .git/refs/heads/master
73622e96d5b5389d63dd74e3c40db9d4c4296ff5 # 1:commit

第二次 git add | git commit

修改 file1 的文件内容为 333

git add file1

root@aliyun:~/blog# git add file1
root@aliyun:~/blog# tree .git/objects/
.git/objects/
├── 55
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550 # file1_modify: blob
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

git commit -m “modify file1”

root@aliyun:~/blog# git commit -m "modify file1"
[master 558e28c] modify file1
 1 file changed, 1 insertion(+), 1 deletion(-)
root@aliyun:~/blog# tree .git/objects/
.git/objects/
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e # 2:commit
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550 # file1_modify: blob
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560 # 2:tree
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

查看 HEAD

root@aliyun:~/blog# cat .git/HEAD
ref: refs/heads/master
root@aliyun:~/blog# cat .git/refs/heads/master
558e28c67089eea9bdfbfd748d32baa8f2ce944e # 指向了第二次 commit 的 hash 值

git add | git commit 实质

git add: 向 .git/objects 添加类型是 blob 的文件 git commit: 向 .git/objects 添加类型是 tree 和 commit 的文件

git branch

List, create, or delete branches Branches in Git are incredibly lightweight as well. They are simply pointers to a specific commit – nothing more. 仅仅是添加了一个指向特定 commit 的指针。 a branch essentially says “I want to include the work of this commit and all parent commits.” 一个分支就是我想要这个 commit 以及这个 commit 的所有 parent commits

创建一个 new-branch 的分支

root@aliyun:~/blog# git branch new-branch
root@aliyun:~/blog# tree .git/
.git/
├── branches
├── COMMIT_EDITMSG
├── config
├── description
├── HEAD
├── hooks
│   ├── applypatch-msg.sample
│   ├── commit-msg.sample
│   ├── fsmonitor-watchman.sample
│   ├── post-update.sample
│   ├── pre-applypatch.sample
│   ├── pre-commit.sample
│   ├── prepare-commit-msg.sample
│   ├── pre-push.sample
│   ├── pre-rebase.sample
│   ├── pre-receive.sample
│   └── update.sample
├── index
├── info
│   └── exclude
├── logs
│   ├── HEAD
│   └── refs
│       └── heads
│           ├── master
│           └── new-branch # git branch new-branch 添加的分支日志
├── objects
│   ├── 55
│   │   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   │   └── bd0ac4c42e46cd751eb7405e12a35e61425550
│   ├── 58
│   │   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
│   ├── 61
│   │   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
│   ├── 73
│   │   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
│   ├── c2
│   │   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
│   ├── d9
│   │   └── 64f468f776fac72a049a884ae24e7dbb838fd0
│   ├── info
│   └── pack
└── refs
    ├── heads
    │   ├── master
    │   └── new-branch # git branch new-branch 添加的 refs
    └── tags

18 directories, 29 files

git branch - -list 查看分支

root@aliyun:~/blog# git branch --list
* master # * 表示当前所在分支
  new-branch # 新创建的 new-branch 分支

git checkout new-branch 切换分支

root@aliyun:~/blog# git checkout new-branch
Switched to branch 'new-branch'
root@aliyun:~/blog# git branch --list
  master
* new-branch

创建分支 new-branch, 并切换到 new-branch 分支.

  1. git branch new-branch
  2. git checkout new-branch 可以简化为:
git checkout -b new-branch

查看 HEAD

root@aliyun:~/blog# cat .git/HEAD
ref: refs/heads/new-branch
root@aliyun:~/blog# cat .git/refs/heads/new-branch
558e28c67089eea9bdfbfd748d32baa8f2ce944e # 指向了第二次 commit 的 hash值

由此可知 git branch new-branch 创建一个分支,实际上做了两件事情:

  1. 添加 .git/logs/refs/heads/new-branch 记录该分支的 log
  2. 添加 .git/refs/heads/new-branch 指向最新的 commit 这也就是 git 创建新的分支如此快的原因.

第三次 git add | git commit

切换到 new-branch 分支, 新建一个 file3 的文件, 内容是 new-branch-file3

git add file3

root@aliyun:~/blog# git add file3
root@aliyun:~/blog# tree .git/objects/
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a # file3
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

9 directories, 8 files
root@aliyun:~/blog# git cat-file -t 2e79
blob
root@aliyun:~/blog# git cat-file -p 2e79
new-branch-file3
root@aliyun:~/blog# git cat-file -s 2e79
17

git commit -m “file3 on new-branch”

root@aliyun:~/blog# git commit -m "add file3 on new-branch"
[new-branch ce907fa] add file3 on new-branch
 1 file changed, 1 insertion(+)
 create mode 100644 file3
root@aliyun:~/blog# tree .git/objects/
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3 # new-branch:tree
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44 # new-branch:commit
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

11 directories, 10 files
root@aliyun:~/blog# git cat-file -t b721
tree
root@aliyun:~/blog# git cat-file -p b721 # 全量的快照(snapshot)
100644 blob 55bd0ac4c42e46cd751eb7405e12a35e61425550    file1
100644 blob c200906efd24ec5e783bee7f23b5d7c941b0c12c    file2
100644 blob 2e799a48d8c045b814c3862af40dea98bdde790a    file3
root@aliyun:~/blog# git cat-file -s b721
99
root@aliyun:~/blog# git cat-file -t ce90
commit
root@aliyun:~/blog# git cat-file -p ce90
tree b72118da210e8e3f4127cfc16cc819eff58e42e3
parent 558e28c67089eea9bdfbfd748d32baa8f2ce944e # 上一次 commit 
author root <root@aliyun> 1578039532 +0800
committer root <root@aliyun> 1578039532 +0800

add file3 on new-branch # commit message
root@aliyun:~/blog# git cat-file -s ce90
208

查看 HEAD

root@aliyun:~/blog# cat .git/HEAD
ref: refs/heads/new-branch # 当前在 new-branch 分支上
root@aliyun:~/blog# cat .git/refs/heads/new-branch
ce907fabd08138058b05428d7cac017507b33c44 # new-branch 分支最新的提交

切换到 master 分支查看 HEAD

root@aliyun:~/blog# git checkout master
Switched to branch 'master'
root@aliyun:~/blog# cat .git/HEAD
ref: refs/heads/master # 当前在 master 分支
root@aliyun:~/blog# cat .git/refs/heads/master
558e28c67089eea9bdfbfd748d32baa8f2ce944e # master 分支最新的提交

查看 master 和 new-branch 两个分支可知, 每一分支对应的 HEAD 和 .git/refs/heads/branch_name 记录的 commit 不同. 这就是 git 分支的实现.

git add | git commit | git branch 图解

git

Fast-forward Merge

两次 git add 和 git commit 之后，创建 new-branch ，在 new-branch 进行了修改。 但是 master 分支没有做任何更改。也就是 master 此时分支落后了 new-branch 分支。 new-branch 分支的修改 master 分支怎样看到呢？可以进行所谓的 Fast-forward merge。

切换到 master 分支

root@aliyun:~/blog# git checkout master  # 切换到 master 分支
Switched to branch 'master'
root@aliyun:~/blog# cat .git/refs/heads/master # master 分支仍然指向第二次的 commit。
558e28c67089eea9bdfbfd748d32baa8f2ce944e
root@aliyun:~/blog# tree .git/objects/ # 查看 objects 对象。
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

11 directories, 10 files

合并 new-branch 分支到 master 分支

root@aliyun:~/blog# git merge new-branch # 合并 new-branch 分支
Updating 558e28c..ce907fa ### 更新 558e 这个object
Fast-forward # fast-forward
 file3 | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 file3
root@aliyun:~/blog# ls
file1  file2  file3
root@aliyun:~/blog# tree .git/objects/ # 查看 objects 对象。并没增加任何 object
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

11 directories, 10 files
root@aliyun:~/blog# cat .git/refs/heads/master 
ce907fabd08138058b05428d7cac017507b33c44 # 更新了 master 指向，指向了 new-branch 的 commit。

Fast-Forward 图解

git fast forward

删除 master 分支上的 file1 文件，然后提交

root@aliyun:~# cp -r blog blog-delete # 复制一份，在 master 分支上删除 file1
root@aliyun:~# cd blog-delete/
root@aliyun:~/blog-delete# ls
file1  file2  file3
root@aliyun:~/blog-delete# tree .git/objects/ # 删除前的 git objects
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

11 directories, 10 files
root@aliyun:~/blog-delete# rm file1 # 删除file1
root@aliyun:~/blog-delete# 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:    file1

no changes added to commit (use "git add" and/or "git commit -a")
root@aliyun:~/blog-delete# git add file1 # 修改添加到 working tree
root@aliyun:~/blog-delete# tree .git/objects/ # 注意，此时的并没有删除或者增加 git objects
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── info
└── pack

11 directories, 10 files
root@aliyun:~/blog-delete# git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

 deleted:    file1

root@aliyun:~/blog-delete# git commit -m "delete file1 on master" # 提交这个修改到 repository
[master f24e8b6] delete file1 on master
 1 file changed, 1 deletion(-)
 delete mode 100644 file1
root@aliyun:~/blog-delete# tree .git/objects/ # 查看此时的 git objects
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c # blob:file1 仍然在 git objects 中
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba  # 新添加一个 tree
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088 # 新添加一个 commit
├── info
└── pack

13 directories, 12 files
root@aliyun:~/blog-delete# git cat-file -s ba61 # ba61 的大小,zlib compressed data
66
root@aliyun:~/blog-delete# git cat-file -t ba61 # ba61 的类型
tree
root@aliyun:~/blog-delete# git cat-file -p ba61
100644 blob c200906efd24ec5e783bee7f23b5d7c941b0c12c file2 # master 分支剩下的 file2
100644 blob 2e799a48d8c045b814c3862af40dea98bdde790a file3 # master 分支剩下的 file3
root@aliyun:~/blog-delete# git cat-file -s f24e
207
root@aliyun:~/blog-delete# git cat-file -t f24e # 新加的 commit object
commit
root@aliyun:~/blog-delete# git cat-file -p f24e
tree ba61ba35d824408f8135ec77b7efdcdfc0281fba # 新加的 tree object
parent ce907fabd08138058b05428d7cac017507b33c44 # delete file1 之前的 commit object
author root <root@aliyun> 1586307459 +0800
committer root <root@aliyun> 1586307459 +0800

delete file1 on master
root@aliyun:~/blog-delete# cat .git/refs/heads/master # master 分支指向了新的 commit
f24e8b6fb771347156b615c795f7fd886dc49088
root@aliyun:~/blog-delete# cat .git/logs/refs/heads/
master      new-branch  
root@aliyun:~/blog-delete# cat .git/logs/refs/heads/master # 查看 master 分支的提交日志
0000000000000000000000000000000000000000 73622e96d5b5389d63dd74e3c40db9d4c4296ff5 root <root@aliyun> 1578027036 +0800 commit (initial): add file1 and file2
73622e96d5b5389d63dd74e3c40db9d4c4296ff5 558e28c67089eea9bdfbfd748d32baa8f2ce944e root <root@aliyun> 1578036269 +0800 commit: modify file1
558e28c67089eea9bdfbfd748d32baa8f2ce944e ce907fabd08138058b05428d7cac017507b33c44 root <root@aliyun> 1586241477 +0800 merge new-branch: Fast-forward
ce907fabd08138058b05428d7cac017507b33c44 f24e8b6fb771347156b615c795f7fd886dc49088 root <root@aliyun> 1586307459 +0800 commit: delete file1 on master

master 分支删除 file1 图解

delete file1 on maste

master 分支删除 file1 图解分析

master 分支 git 中删除一个文件的实质是：

  1. 生成一个 tree object ba61ba，指向剩下的每一个文件的最新的 blob object。blob c20090 file2 和 blob 2e799a file3
  2. 生成一个 commit f24e8b 节点，指向本次提交的上一个 commit object(ce907f) 和这次提交生成的 tree object(ba61ba)。
  3. 移动 master 和 HEAD 的指向，指向本次提交的 commit object f24e8b。
  4. 在 master 的 .git/logs/refs/heads/master 分支添加本次提交的 git log。
  5. 删除 file1，但是 git object 下 file1 的 blob(58c9bd) 并没有删除。这也意味着可以恢复 file1。
  6. 其他分支同理。

合并分支(combine work)

使用 git merge

Merging in Git creates a special commit that has two unique parents. A commit with two parents essentially means “I want to include all the work from this parent over here and this one over here, and the set of all their parents.”

new-branch 分支添加 file4

new-branch 分支添加 file4 步骤
root@aliyun:~# cd blog-delete
root@aliyun:~/blog-delete# ls
file2  file3
root@aliyun:~/blog-delete# git branch --list  # 查看分支
* master
  new-branch
root@aliyun:~/blog-delete# git checkout new-branch  # 切换到 new-branch
Switched to branch 'new-branch'
root@aliyun:~/blog-delete# ls
file1  file2  file3
root@aliyun:~/blog-delete# echo 444 > file4 # 创建 file4
root@aliyun:~/blog-delete# git status
On branch new-branch
Untracked files:
  (use "git add <file>..." to include in what will be committed)

 file4

nothing added to commit but untracked files present (use "git add" to track)
root@aliyun:~/blog-delete# tree .git/objects/
.git/objects/
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

13 directories, 12 files
root@aliyun:~/blog-delete# git add file4 # 添加 file4
root@aliyun:~/blog-delete# tree .git/objects/
.git/objects/
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a # blob:file4
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

14 directories, 13 files
root@aliyun:~/blog-delete# git commit -m "add file4 on new-branch"
[new-branch c9918ce] add file4 on new-branch
 1 file changed, 1 insertion(+)
 create mode 100644 file4
root@aliyun:~/blog-delete# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491 # 4:tree
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a # blob:file4
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44 # 4:commit
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

16 directories, 15 files
root@aliyun:~/blog-delete# git cat-file -s 0977 # 新加的 tree object
132
root@aliyun:~/blog-delete# git cat-file -t 0977
tree
root@aliyun:~/blog-delete# git cat-file -p 0977 # new-branch 分支上所有文件的 snapshot
100644 blob 55bd0ac4c42e46cd751eb7405e12a35e61425550 file1
100644 blob c200906efd24ec5e783bee7f23b5d7c941b0c12c file2
100644 blob 2e799a48d8c045b814c3862af40dea98bdde790a file3
100644 blob 1e6fd033863540bfb9eadf22019a6b4b3de7d07a file4
root@aliyun:~/blog-delete# git cat-file -s 1e6f # new-branch 分支新加的 file4
4
root@aliyun:~/blog-delete# git cat-file -t 1e6f 
blob
root@aliyun:~/blog-delete# git cat-file -p 1e6f
444
root@aliyun:~/blog-delete# git cat-file -s c991 # 新的 commit object
208
root@aliyun:~/blog-delete# git cat-file -t c991
commit
root@aliyun:~/blog-delete# git cat-file -p c991
tree 0977e7b9e8643eaa75b679d7e82b048723e9f491 # 本次生成的 tree object
parent ce907fabd08138058b05428d7cac017507b33c44 # 上一次 commit
author root <root@aliyun> 1586330993 +0800
committer root <root@aliyun> 1586330993 +0800

add file4 on new-branch # git commit-m 的信息
root@aliyun:~/blog-delete-new-branch-file4# git checkout master # 切换到 master
Switched to branch 'master'
root@aliyun:~/blog-delete-new-branch-file4# ls # 查看 master 分支的文件
file2  file3
root@aliyun:~/blog-delete-new-branch-file4# tree .git/objects/ # 在 master 分支查看 objects
.git/objects/ # 和在 new-branch 分支上看到的一样
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

16 directories, 15 files
new-branch 分支添加 file4 图解

new-branch-add-file4

master 分支添加 file5

master 分支添加 file5 步骤
root@aliyun:~# cp -r blog-delete blog-delete-master-file5 # 复制一份
root@aliyun:~# cd blog-delete-master-file5/
root@aliyun:~/blog-delete-master-file5# ls
file1  file2  file3  file4
root@aliyun:~/blog-delete-master-file5# git branch --list 
  master
* new-branch
root@aliyun:~/blog-delete-master-file5# git checkout master # 切换到 master
Switched to branch 'master'
root@aliyun:~/blog-delete-master-file5# echo 555 > file5 创建 file5
root@aliyun:~/blog-delete-master-file5# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

16 directories, 15 files
root@aliyun:~/blog-delete-master-file5# git add file5 
root@aliyun:~/blog-delete-master-file5# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 37
│   └── 49383ded246790596d2f39db4dd8b71f525bbc
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── info
└── pack

17 directories, 16 files
root@aliyun:~/blog-delete-master-file5# git commit -m "add file5 on master"
[master 3de903f] add file5 on master
 1 file changed, 1 insertion(+)
 create mode 100644 file5
root@aliyun:~/blog-delete-master-file5# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 37
│   └── 49383ded246790596d2f39db4dd8b71f525bbc # blob:file5
├── 3d
│   └── e903f0c523d57b4880be68bacb1eaa1195ebac #5:commit
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── f5
│   └── 4ecef60b4376ae5531032cbeaade01184da4fa # 5:tree
├── info
└── pack

19 directories, 18 files
root@aliyun:~/blog-delete-master-file5# git cat-file -t 3de90 # 本次的 commit object
commit
root@aliyun:~/blog-delete-master-file5# git cat-file -s 3de90
204
root@aliyun:~/blog-delete-master-file5# git cat-file -p 3de90
tree f54ecef60b4376ae5531032cbeaade01184da4fa
parent f24e8b6fb771347156b615c795f7fd886dc49088
author root <root@aliyun> 1586340888 +0800
committer root <root@aliyun> 1586340888 +0800

add file5 on master
root@aliyun:~/blog-delete-master-file5# git cat-file -t f54ece # 本次的 tree objet
tree
root@aliyun:~/blog-delete-master-file5# git cat-file -s f54ece
99
root@aliyun:~/blog-delete-master-file5# git cat-file -p f54ece
100644 blob c200906efd24ec5e783bee7f23b5d7c941b0c12c file2 # master 分支上的 file2
100644 blob 2e799a48d8c045b814c3862af40dea98bdde790a file3 # master 分支上的 file3
100644 blob 3749383ded246790596d2f39db4dd8b71f525bbc file5 # master 分支上的 file5
root@aliyun:~/blog-delete-master-file5# git cat-file -t 374938 # file5
blob
root@aliyun:~/blog-delete-master-file5# git cat-file -s 374938
4
root@aliyun:~/blog-delete-master-file5# git cat-file -p 374938
555
master 分支添加 file5 图解

master-add-file5

master 分支合并到 new-branch 分支

master 分支合并到 new-branch 分支步骤
root@aliyun:~# cp -r blog-delete-master-file5/ blog-delete-file4-file5-merge
root@aliyun:~# cd blog-delete-file4-file5-merge/
root@aliyun:~/blog-delete-file4-file5-merge# git branch --list
* master
  new-branch
root@aliyun:~/blog-delete-file4-file5-merge# tree .git/objects/
09/   1e/   2e/   37/   3d/   55/   58/   61/   73/   b7/   ba/   c2/   c9/   ce/   d9/   f2/   f5/   info/ pack/ 
root@aliyun:~/blog-delete-file4-file5-merge# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 37
│   └── 49383ded246790596d2f39db4dd8b71f525bbc
├── 3d
│   └── e903f0c523d57b4880be68bacb1eaa1195ebac
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── f5
│   └── 4ecef60b4376ae5531032cbeaade01184da4fa
├── info
└── pack

19 directories, 18 files
root@aliyun:~/blog-delete-file4-file5-merge# git checkout new-branch # 切换到 new-branch
Switched to branch 'new-branch'
root@aliyun:~/blog-delete-file4-file5-merge# git merge master # 把 master 分支合并到当前分支，也就是 new-branch 分支
Removing file1 # master 分支上删除了 file1，new-branch 分支合并时也会删掉。
Merge made by the 'recursive' strategy.
 file1 | 1 -
 file5 | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)
 delete mode 100644 file1
 create mode 100644 file5
root@aliyun:~/blog-delete-file4-file5-merge# tree .git/objects/
.git/objects/
├── 09
│   └── 77e7b9e8643eaa75b679d7e82b048723e9f491
├── 1e
│   └── 6fd033863540bfb9eadf22019a6b4b3de7d07a
├── 2e
│   └── 799a48d8c045b814c3862af40dea98bdde790a
├── 37
│   └── 49383ded246790596d2f39db4dd8b71f525bbc
├── 3d
│   └── e903f0c523d57b4880be68bacb1eaa1195ebac
├── 4f
│   └── ed41461bcfd7157b71d757b2fe70e3d7317f94 # 6:tree 合并生成的 tree object
├── 55
│   ├── 8e28c67089eea9bdfbfd748d32baa8f2ce944e
│   └── bd0ac4c42e46cd751eb7405e12a35e61425550
├── 58
│   └── c9bdf9d017fcd178dc8c073cbfcbb7ff240d6c
├── 61
│   └── 74c3edb1e8dc4f1692b69fd43c8c6af85ce560
├── 73
│   └── 622e96d5b5389d63dd74e3c40db9d4c4296ff5
├── b7
│   └── 2118da210e8e3f4127cfc16cc819eff58e42e3
├── ba
│   └── 61ba35d824408f8135ec77b7efdcdfc0281fba
├── c2
│   └── 00906efd24ec5e783bee7f23b5d7c941b0c12c
├── c9
│   └── 918cea80e46648c4e98da5b1c4b072f0794795
├── ce
│   └── 907fabd08138058b05428d7cac017507b33c44
├── d9
│   └── 64f468f776fac72a049a884ae24e7dbb838fd0
├── f2
│   └── 4e8b6fb771347156b615c795f7fd886dc49088
├── f5
│   └── 4ecef60b4376ae5531032cbeaade01184da4fa
├── fc
│   └── 094b5b4e7a0f4028c5735d95f844b1aea1a9b6 # 6:commit 合并生成的 commit object
├── info
└── pack

21 directories, 20 files
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -s 4fed41
132
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -t 4fed41
tree
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -p 4fed41
100644 blob c200906efd24ec5e783bee7f23b5d7c941b0c12c file2 
100644 blob 2e799a48d8c045b814c3862af40dea98bdde790a file3
100644 blob 1e6fd033863540bfb9eadf22019a6b4b3de7d07a file4
100644 blob 3749383ded246790596d2f39db4dd8b71f525bbc file5
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -s fc094b # 本次合并生成的 commit object
270
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -t fc094b
commit
root@aliyun:~/blog-delete-file4-file5-merge# git cat-file -p fc094b
tree 4fed41461bcfd7157b71d757b2fe70e3d7317f94 # 本次合并时两个分支的 snapshot
parent c9918cea80e46648c4e98da5b1c4b072f0794795 # new branch 分支合并时最新的 commit
parent 3de903f0c523d57b4880be68bacb1eaa1195ebac # master 分支合并时最新的 commit
author root <root@aliyun> 1586344983 +0800
committer root <root@aliyun> 1586344983 +0800

Merge branch 'master' into new-branch

root@aliyun:~/blog-delete-file4-file5-merge# cat .git/refs/heads/new-branch # new branch 已经指向了新生成的 commit 节点
fc094b5b4e7a0f4028c5735d95f844b1aea1a9b6
root@aliyun:~/blog-delete-file4-file5-merge# cat .git/refs/heads/master # master 分支没有发生改变
3de903f0c523d57b4880be68bacb1eaa1195ebac
root@aliyun:~/blog-delete-file4-file5-merge# cat .git/logs/refs/heads/new-branch  # new branch 分支 log
0000000000000000000000000000000000000000 558e28c67089eea9bdfbfd748d32baa8f2ce944e root <root@aliyun> 1578037705 +0800 branch: Created from master
558e28c67089eea9bdfbfd748d32baa8f2ce944e ce907fabd08138058b05428d7cac017507b33c44 root <root@aliyun> 1578039532 +0800 commit: add file3 on new-branch
ce907fabd08138058b05428d7cac017507b33c44 c9918cea80e46648c4e98da5b1c4b072f0794795 root <root@aliyun> 1586330993 +0800 commit: add file4 on new-branch
c9918cea80e46648c4e98da5b1c4b072f0794795 fc094b5b4e7a0f4028c5735d95f844b1aea1a9b6 root <root@aliyun> 1586344983 +0800 merge master: Merge made by the 'recursive' strategy. # 本次 merge 的 log
master 分支合并到 new-branch 图解

git-merge-master master 分支合并到 new-branch 分支实质：

  1. 生成一个新的 tree object 4f1d41 指向 master 分支和 new-branch 分支共有的文件 blob。
  2. 生成一个新的 commit object fc094b 指向新生成的 tree object 4f1d41以及合并前的 master 分支的 commit 和 new-branch 分支的 commit。
  3. .git/refs/heads/new-branch指向新生成的 commit object fc094b。
  4. .git/logs/refs/heads/new-branch 添加本次 merge 的 log。
  5. .git/refs/heads/master master 分支的指向并没有发生改变。

Reference

  1. git-under-the-hood
  2. Bilibili-git-under-the-hood
  3. SHA-1
  4. git-branch
  5. visual-git-reference
  6. visualized-useful-git-commands