http://blog.csdn.net/csfreebird/article/details/7583363

1.HEAD基礎

git checkout 實際上是修改HEAD文件的內容，讓其指向不同的branch。

HEAD文件指向的branch就是當前branch.

一般來講，HEAD的內容是指向staging（暫存區）的master文件的。

[plain]?view plaincopyprint?

ref:?refs/heads/master??

當然也可指向其他索引文件，不管怎么樣，這個索引文件的內容又由git reset控制。

通過git branch命令看到的結果和HEAD文件內容一致。

[plain]?view plaincopyprint?

$?git?branch?-v??

*?master?1aea8d9?[ahead?1]?add?test?file?x??

2.最簡單用法

git checkout最簡單的用法，顯示工作區，暫存區和HEAD的差異：

[plain]?view plaincopyprint?

$?git?checkout??

M???x??

Your?branch?is?ahead?of?'origin/master'?by?1?commit.??

意思是我本地倉庫比遠程倉庫領先一個提交操作。git checkout HEAD 功能相同。

如果用-a 參數，可以看到很多branch，包括遠程的branch，比如：

[plain]?view plaincopyprint?

git?branch?-a??

*?master??

??remotes/origin/HEAD?->?origin/master??

??remotes/origin/develop??

??remotes/origin/issue_193??

??remotes/origin/issue_210??

??remotes/origin/master??

3.detached HEAD

如果讓HEAD文件指向一個commit id，那就變成了detached HEAD。git checkout 可以達到這個效果，用下面的命令：

[plain]?view plaincopyprint?

git?checkout?1aea8d9^??

laea8d9是最近的一次commit id，^指的是之前一次，因此上面的操作結果是讓HEAD文件包含了倒數第二次提交的id.

下面演示如何進入datached HEAD狀態，并恢復回來。

[plain]?view plaincopyprint?

$?git?branch?-v??

*?master?89f8dae?[ahead?2]?update?x??

$?git?checkout?89f8dae^??

Note:?checking?out?'89f8dae^'.??

??

You?are?in?'detached?HEAD'?state.?You?can?look?around,?make?experimental??

changes?and?commit?them,?and?you?can?discard?any?commits?you?make?in?this??

state?without?impacting?any?branches?by?performing?another?checkout.??

??

If?you?want?to?create?a?new?branch?to?retain?commits?you?create,?you?may??

do?so?(now?or?later)?by?using?-b?with?the?checkout?command?again.?Example:??

??

??git?checkout?-b?new_branch_name??

??

HEAD?is?now?at?1aea8d9...?add?test?file?x??

好，現在恢復回來。

[plain]?view plaincopyprint?

$?git?checkout?master??

Previous?HEAD?position?was?1aea8d9...?add?test?file?x??

Switched?to?branch?'master'??

Your?branch?is?ahead?of?'origin/master'?by?2?commits.??

我并不清楚detached HEAD有何實際用處，反正就是一個讓HEAD隨便指向某個commit id，而不在乎是哪個branch的功能。

http://stackoverflow.com/questions/10228760/fix-a-git-detached-head

Detached head means you are no longer on a branch, you have checked out a single commit in the history (in this case the commit previous to HEAD, i.e. HEAD^).

You only need to checkout the branch you were on, e.g.

git checkout master

Next time you have changed a file and want to restore it to the state it is in the index, don't delete the file first, just do

git checkout -- path/to/foo

This will restore the file foo to the state it is in the index.

總結

以上是生活随笔為你收集整理的git checkout之一 HEAD基本和detached 状态的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。