这个〜1在这个git reset命令中意味着什么？ [英] What does the ~1 mean in this git reset command?

问题描述

git reset HEAD〜1

我以为〜1的意思是：开始在HEAD处，跟随1个链接，并将HEAD标记设置为新的提交节点。我期待

git的复位HEAD〜2

按照2个链接，然后设置HEAD标签。但是，如果我尝试它，则会收到错误消息：

  $ git reflog 
 c83bbda HEAD @ {0}：复位：移动到HEAD〜1个
 44c3540 HEAD @ {1}：承诺：你将垃圾很快
 c83bbda HEAD @ {2}：重置：移动到HEAD〜1个
 aee7955 HEAD @ {3}：承诺：回至4行
 c83bbda HEAD @ {4}：复位：移动到HEAD〜1个
 19ec1d5 HEAD @ {5}：提交：3行
 c83bbda HEAD @ {6}：复位：移动到HEAD〜1个
 a049538 HEAD @ {7}：提交：添加新行
 c83bbda HEAD @ {8}：提交（初始）：第一承诺
 
 
 $ git reset --hard HEAD〜2 
致命：模棱两可的说法'HEAD〜2'：未知版本或路径不在工作树中。 
使用' - '分隔修订版本的路径，如下所示：
'git< command> [< revision> ...]  -  [< file>]'
  

显然我错了，但git reset的doc页面在澄清这个方面并不是很有用。所以，〜1是什么意思，为什么我需要它？

解决方案

HEAD〜1 是 HEAD 的第一个父项，而 HEAD〜2 是第一个父项 HEAD 的第一个父元素，等等（对于某些n，所以 HEAD〜n 就像 HEAD 后跟n ^ 符号，并且没有数字），所有的细节都在 GIT-REV-解析的手册。

在将 git reset 与修订版从 HEAD 。 git reset 通常会改变 HEAD 的值，例如：

  $ git checkout master＃现在位于master分支的顶端
 $ git分支save master＃将分支尖端复制到另一个标签，保管
 $ git reset HEAD ^＃或git reset HEAD〜1 
  

将 HEAD （和 master ）移至其第一个父项。命名该父项的另一种方法是 save ^ ，另一种是 save〜1 。但是，移动完成后， HEAD 现在将该修订名称命名为 HEAD ^ > parent：

  $ git reset HEAD ^ 
  

让你回到另一个步骤，使现在 master 和 HEAD >>命名与 save〜2 名称相同的提交。使用 git rev-parse 可以很容易地看到，它告诉你一些符号名映射到的提交ID：

'pre> $ GIT中REV-解析保存〜2主
0f5a13497dd3da8aff8e452c8f56630f83253e79
0f5a13497dd3da8aff8e452c8f56630f83253e79


此时，您可以使用以下命令将 master 恢复到保存点：

  $ git重置保存
  

移动 HEAD 和 master 回到已保存的版本，然后您可以删除 save

  $ git branch -d save 
  

请注意，您也可以使用 git tag 来保存保存点：分支和标签是当在分支上（标签不移动，分支执行）和签出（标签将您置于分离头部=不是分支状态时，分支上的新签入行为名称将您置于分支状态）。

git reset HEAD~1

I was under the impression that the ~1 meant: start at the HEAD, follow 1 link, and set the HEAD tag to that new commit node. I was expecting

git reset HEAD~2

to follow 2 links and then set the HEAD tag. However, if I try it, I get an error:

$ git reflog
c83bbda HEAD@{0}: reset: moving to HEAD~1
44c3540 HEAD@{1}: commit: you will be garbage soon
c83bbda HEAD@{2}: reset: moving to HEAD~1
aee7955 HEAD@{3}: commit: back to 4 lines
c83bbda HEAD@{4}: reset: moving to HEAD~1
19ec1d5 HEAD@{5}: commit: 3 lines
c83bbda HEAD@{6}: reset: moving to HEAD~1
a049538 HEAD@{7}: commit: added new line
c83bbda HEAD@{8}: commit (initial): first commit


$ git reset --hard HEAD~2
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>...]'

Apparently I was mistaken, but the doc page for git reset is not very useful in clarifying this. So, what does the ~1 mean and why do I need it?

解决方案

HEAD~1 is "the first parent of HEAD", while HEAD~2 is "the first parent of the first parent of HEAD, and so on (so HEAD~n for some n is like HEAD followed by n ^ symbols and no numbers). Again, all the specifics are in the git-rev-parse manual page.

Be careful when mixing git reset with "revisions counting backwards from HEAD". git reset will, in general, change the value of HEAD, e.g.:

$ git checkout master    # now on tip of "master" branch
$ git branch save master # copy branch tip to another label, for safekeeping
$ git reset HEAD^        # or git reset HEAD~1

moves HEAD (and master) to its first parent. Another way to name that parent is save^, and yet another is save~1. After the move finishes, though, HEAD now names that parent revision, so HEAD^ names its parent:

$ git reset HEAD^

moves you back another step, so that master and HEAD now name the same commit that save~2 names. This is easy to see using git rev-parse, which tells you the commit-ID that some symbolic-name maps to:

$ git rev-parse save~2 master
0f5a13497dd3da8aff8e452c8f56630f83253e79
0f5a13497dd3da8aff8e452c8f56630f83253e79

At this point, you can restore master to the save-point with:

$ git reset save

which moves HEAD and master back to the saved revision, and then you can delete save safely if you like:

$ git branch -d save

Note that you could save a save-point with git tag too: the only difference between a branch and a tag is the behavior of new check-ins when "on a branch" (tags don't move, branches do) and check-outs (tags put you in "detached HEAD" = not-on-a-branch state, branch names put you in "on-a-branch" state).

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