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7.6 0425 Git branch 分支

Examle 1 直線進行的分支

1. git branch 列出所有分支

/Users/tingtinghsu/git-examples/git-branch1
tingdeAir:git-branch1 tingtinghsu$ git branch
* master

2. git branch cat 建立新分支

tingdeAir:git-branch1 tingtinghsu$ git branch
  cat /* 貼貼紙 */
* master

3. git checkout cat 切換到cat分支

HEAD: 上帝視角

  1. HEAD移動到cat貼紙，並且跟著cat
  2. 專案會變成cat貼紙指到的Commit狀態
  3. 目前cat跟master所在位置一樣
tingdeAir:git-branch1 tingtinghsu$ git checkout cat
Switched to branch 'cat'
tingdeAir:git-branch1 tingtinghsu$ git branch
* cat
  master

3-1 在cat branch送commit

使用checkout之後送commit

  1. cat貼紙與HEAD往前移動(如下圖，cat分支變為粗體字)
  2. 其他分支留在原地

圖:cat貼紙與HEAD往前移動

tingdeAir:git-branch1 tingtinghsu$ git branch
* cat
  master

tingdeAir:git-branch1 tingtinghsu$ touch .keep
tingdeAir:git-branch1 tingtinghsu$ git status
On branch cat
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	.keep
    
tingdeAir:git-branch1 tingtinghsu$ git add .
tingdeAir:git-branch1 tingtinghsu$ git commit -m "add cat branch"
[cat 8fded81] add cat branch
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 .keep
tingdeAir:git-branch1 tingtinghsu$ git log --oneline
8fded81 add cat branch
865f98a add hello-world file
e12d8ef add database.yml in config folder
85e7e30 add hello
657fce7 add container
abb4f43 update index page
cef6e40 create index page
cc797cd init commit

3-2 git merge 合併分支 (先切回master)

跟master很像的分支，合併時會使用fast-forward快轉
（git圖示上master往前走，沒有小耳朵）

  1. 切換回master分支 git checkout master
    • HEAD移動到master貼紙
    • 專案會變成master貼紙指到的commit狀態 (如下圖，master分支變回粗體字)

圖:專案會變成master貼紙指到的commit狀態

  1. 合併cat分支 git merge cat
    • master與HEAD移動到cat貼紙的所在地
    • 快轉(Fast-forward)合併

=> 合併分支可以看成在移動貼紙(如下圖，master貼紙移動到與cat貼紙相同的commit)

tingdeAir:git-branch1 tingtinghsu$ git branch
* cat
  master
  
tingdeAir:git-branch1 tingtinghsu$ git checkout master
Switched to branch 'master'

tingdeAir:git-branch1 tingtinghsu$ git merge cat
Updating 865f98a..8fded81
Fast-forward
 .keep | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 .keep

tingdeAir:git-branch1 tingtinghsu$ git log --oneline
8fded81 add cat branch
865f98a add hello-world file
e12d8ef add database.yml in config folder
85e7e30 add hello
657fce7 add container
abb4f43 update index page
cef6e40 create index page
cc797cd init commit

4. git branch -d刪掉已合併的分支

  1. 把cat貼紙撕起來
  2. Commit 或是檔案不會因此受到影響

=> Git 的本體是commit, 分支只是浮雲

tingdeAir:git-branch1 tingtinghsu$ git branch -d cat
Deleted branch cat (was 8fded81).

Examle 2 複雜一點的分支

y型merge

1. git branch dog 建立新分支

在目前HEAD所在地貼dog貼紙

tingdeAir:git-branch1 tingtinghsu$ git branch dog
tingdeAir:git-branch1 tingtinghsu$ git branch
  dog
* master
  rabbit
tingdeAir:git-branch1 tingtinghsu$

2. git checkout dog 切換到dog分支

  1. HEAD移動到dog分支
  2. 專案會變成dog貼紙指到的Commit狀態
  3. 目前dog跟master所在位置一樣
tingdeAir:git-branch1 tingtinghsu$ git checkout dog
Switched to branch 'dog'
tingdeAir:git-branch1 tingtinghsu$ git branch
* dog
  master
  rabbit

2-1 在dog branch送commit

再進行一次存檔

  1. dog貼紙與HEAD往前移動
  2. 其他分支貼紙留在原地

dog貼紙與HEAD往前移動

HEAD像是令牌，只有領到令牌的分支才可以往前移動

tingdeAir:git-branch1 tingtinghsu$ git commit -m "add dog 1"
[dog e560a0e] add dog 1
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 .keepdog

2-2 在dog branch再送一次commit

tingdeAir:git-branch1 tingtinghsu$ git add .
tingdeAir:git-branch1 tingtinghsu$ git commit -m "add dog 2"
[dog 3f699df] add dog 2
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 .keeptwodogs

第二個分支長太大，這時候的合併就沒辦法fast forward了

分支長太大的合併就沒辦法fast forward

2-3. git merge rabbit : 在dog分支合併rabbit分支

rabbit分支也commit過一次，若此時dog分支想要合併rabbit分支:

1.長出一個合併的commit (dog和rabbit分支的公證人)
2.dog貼紙和HEAD往新的commit移動

合併分支時產生小耳朵

tingdeAir:git-branch1 tingtinghsu$ git checkout rabbit
Switched to branch 'rabbit'
tingdeAir:git-branch1 tingtinghsu$ ls
config		hello.html	index.html	welcome.html
tingdeAir:git-branch1 tingtinghsu$ touch rabbit
tingdeAir:git-branch1 tingtinghsu$ git add .
tingdeAir:git-branch1 tingtinghsu$ git commit -m "add rabbit"
[rabbit 6001538] add rabbit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 rabbit

tingdeAir:git-branch1 tingtinghsu$ git checkout dog
Switched to branch 'dog'
tingdeAir:git-branch1 tingtinghsu$ git merge rabbit
Merge made by the 'recursive' strategy.
 rabbit | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 rabbit

＊在Sourcetree打勾Checkout New Branch，代表建立分支之後立即切換過去該branch。

Example 3 讓合併的節點消失掉git rebase

git rebase: 變換根基/嫁接

注意: 在git的世界裡，commit沒有辦法刪除，但透過git rebase可以將歷史commit記錄變成直線。

現在有dog與bird分支
dog分支與bird分支

在HEAD是dog, git rebase bird : dog踩在bird分支的頭上

  1. 複製一份dog的commit接到bird的commit後面，形成新的commit
  2. HEAD移動到新的commit
  3. dog貼紙移動到新的commit, HEAD指向bird貼紙
  4. bird貼紙從舊的分支commit脫離（如下圖：bird分支已消失，歷史紀錄變成直線）

bird分支的舊commit脫離

tingdeAir:git-branch1 tingtinghsu$ git rebase bird
First, rewinding head to replay your work on top of it...
Applying: add dog3

merge和rebase的使用時機

rebase
優點:
拿來整理過多節點的時候，把節點拉成同條

缺點:
看不太出來歷史軌跡

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