一、分离头指针
正常情况下，在通过git checkout下令切换分支时，在下令反面跟着的是分支名（例如master、temp等）或分支名对应commit的哈希值。
非正常情况下，git checkout切换分支时反面跟了一个非分支对应commit的哈希值，此时就会产生分离头指针题目。
例如，项目标版本汗青中有如下3次commit，其中两个分别是temp分支和master分支；此时将分支切换到第三个commit（也就是非temp、master分支）上，就会出现detached HEAD提示，即分离头指针题目。
- git log
- commit e5d60c7d913d427b2e2161f717dff97249dd1f9b (HEAD -> temp)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:22:51 2023 +0800
- add temp_test
- commit 01df9fd5e046f104312468746168b027f4285c5c (master)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:22:04 2023 +0800
- add file1
- commit db2d096bf27e4e8f4ca42e8b185e973b05e186df
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:21:31 2023 +0800
- add readme
- git checkout db2d096bf27e4e
- Note: switching to 'db2d096bf27e4e'.
- 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 switching back to a branch.
- If you want to create a new branch to retain commits you create, you may
- do so (now or later) by using -c with the switch command. Example:
- git switch -c <new-branch-name>
- Or undo this operation with:
- git switch -
- Turn off this advice by setting config variable advice.detachedHead to false
- HEAD is now at db2d096 add readme
- git log --all
- commit e5d60c7d913d427b2e2161f717dff97249dd1f9b (temp)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:22:51 2023 +0800
- add temp_test
- commit 01df9fd5e046f104312468746168b027f4285c5c (master)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:22:04 2023 +0800
- add file1
- commit db2d096bf27e4e8f4ca42e8b185e973b05e186df (HEAD)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:21:31 2023 +0800
- add readme
当切换到某个commit时，git会提示已进入到分离头指针状态，并显示在该状态下可进行的操作：
a）可在该HEAD（commit）中进行测试、提交或取消更改，当切回到分支时不会影响到分支，但此前在此commit上做的全部操作都会丢失
b）若想保留在该commit上的变动，可通过git switch -c branch_name进行分支添加
分离头指针指向某个commit后，若再切换回master分支或其他分支时，没有为该commit新建分支，则全部在该commit上做的操作都将丢失。
1）在commit上进行修改操作，并进行commit提交
- vi readme
- git status
- HEAD detached at db2d096
- Changes not staged for commit:
- (use "git add <file>..." to update what will be committed)
- (use "git restore <file>..." to discard changes in working directory)
- modified: readme
- no changes added to commit (use "git add" and/or "git commit -a")
- git add readme
- warning: LF will be replaced by CRLF in readme.
- The file will have its original line endings in your working directory
- git commit -m "detach modify file"
- [detached HEAD 69cde78] detach modify file
- 1 file changed, 1 insertion(+)
- git log
- commit 69cde788edb4184538f2155ea5e062f5649e8781 (HEAD)
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 15:56:42 2023 +0800
- detach modify file
- commit db2d096bf27e4e8f4ca42e8b185e973b05e186df
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:21:31 2023 +0800
- add readme
- git checkout master
- Warning: you are leaving 1 commit behind, not connected to
- any of your branches:
- 69cde78 detach modify file
- If you want to keep it by creating a new branch, this may be a good time
- to do so with:
- git branch <new-branch-name> 69cde78
- Switched to branch 'master'
- git log --all --graph # gitk --all 可调出图形界面
- * commit e5d60c7d913d427b2e2161f717dff97249dd1f9b (temp)
- | Author: xxx <xxx@163.com>
- | Date: Thu Nov 9 10:22:51 2023 +0800
- |
- | add temp_test
- |
- * commit 01df9fd5e046f104312468746168b027f4285c5c (HEAD -> master)
- | Author: xxx <xxx@163.com>
- | Date: Thu Nov 9 10:22:04 2023 +0800
- |
- | add file1
- |
- * commit db2d096bf27e4e8f4ca42e8b185e973b05e186df
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:21:31 2023 +0800
- add readme
- git branch detach_branch 69cde78 # 复制前面git提示的命令语句，添加分支名称即可
- git log --all --graph # 此时版本历史中就能看到detach分支的信息
- * commit 69cde788edb4184538f2155ea5e062f5649e8781 (detach_branch)
- | Author: xxx <xxx@163.com>
- | Date: Thu Nov 9 15:56:42 2023 +0800
- |
- | detach modify file
- |
- | * commit e5d60c7d913d427b2e2161f717dff97249dd1f9b (temp)
- | | Author: xxx <xxx@163.com>
- | | Date: Thu Nov 9 10:22:51 2023 +0800
- | |
- | | add temp_test
- | |
- | * commit 01df9fd5e046f104312468746168b027f4285c5c (HEAD -> master)
- |/ Author: xxx <xxx@163.com>
- | Date: Thu Nov 9 10:22:04 2023 +0800
- |
- | add file1
- |
- * commit db2d096bf27e4e8f4ca42e8b185e973b05e186df
- Author: xxx <xxx@163.com>
- Date: Thu Nov 9 10:21:31 2023 +0800
- add readme
gitk --all
三、比较commit内容
可通过git diff下令来比较两个commit之间的内容差异。
- git log --all --oneline
- 69cde78 (detach_branch) detach modify file
- e5d60c7 (temp) add temp_test
- 01df9fd (HEAD -> master) add file1
- db2d096 add readme
- git diff 69cde78 e5d60c7 # 后跟两个commit哈希值
- diff --git a/file1 b/file1
- new file mode 100644
- index 0000000..e69de29
- diff --git a/readme b/readme
- index 9fa5398..e69de29 100644
- --- a/readme
- +++ b/readme
- @@ -1 +0,0 @@
- -test detach
- diff --git a/temp_test b/temp_test
- new file mode 100644
- index 0000000..e69de29
- git diff HEAD HEAD^ # HEAD^ 表示HEAD指针对应commit的父commit
- diff --git a/file1 b/file1
- deleted file mode 100644
- index e69de29..0000000
- git diff HEAD HEAD^^ # HEAD^^ 父亲的父亲
- fatal: ambiguous argument 'HEAD^^': unknown revision or path not in the working tree.
- Use '--' to separate paths from revisions, like this:
- 'git <command> [<revision>...] -- [<file>...]'
- git diff HEAD HEAD~1 # HEAD~1 <==> HEAD^
- diff --git a/file1 b/file1
- deleted file mode 100644
- index e69de29..0000000
- git diff HEAD HEAD~2 # HEAD~2 <==> HEAD^^
- fatal: ambiguous argument 'HEAD~2': unknown revision or path not in the working tree.
- Use '--' to separate paths from revisions, like this:
- 'git <command> [<revision>...] -- [<file>...]'
一般情况下，我们切换分支只在已有的几个分支名称之间来回切换，但遇到切换到某个commit的情况时，即出现分离头指针题目时，要懂得该题目是如何产生的，并通过什么样的操作步骤可以去解决它，而不影响到现有分支。此外，分离头指针现象也可以便于我们进行相关的测试，在不影响现有生产的条件下。
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