`checkout -B` vs.`symbolic-ref` [英] `checkout -B` vs. `symbolic-ref`

问题描述

以下命令等效吗?如果没有，有什么区别?

Are the following commands equivalent? If not, what are the differences?

git checkout -B a_branch

和

git branch -f a_branch HEAD
git symbolic-ref HEAD refs/heads/a_branch

git branch -f a_branch HEAD
git symbolic-ref HEAD refs/heads/a_branch

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另请参见此相关帖子.

推荐答案

是的，它们非常接近，以至于它们可能完全相同.

Yes, they are extremely close, so much so that they might as well be identical.

如果您稍微更改其中一个，它们的紧密度将大大降低.考虑您可以将其用作:

They become much less close if you change one of them slightly. Consider that you can use this as:

git checkout -B name commit-specifier

git checkout -B name commit-specifier

以及:

git checkout -B name

git checkout -B name

这实际上意味着:

git checkout -B name HEAD

git checkout -B name HEAD

如文档所述， -b和-B标志是某些替代命令序列的事务等效项".如果这些命令在执行过程中某处失败(或确实会失败)，则或-B操作将被抑制.实际上，当您有未提交的更改会被结帐覆盖时，git checkout commit-specifier实际上可能会失败.

As the documentation says, the -b and -B flags are the "transactional equivalent" of some alternative sequence of commands. If those commands would (or do) fail somewhere along the way, the -b or -B action is suppressed. And git checkout commit-specifier can in fact fail, when you have uncommitted changes that would be overwritten by checkout.

但是，git checkout HEAD 应该永远都不会失败.鉴于它实际上不会失败，因此-B操作的事务性变得不重要.现在，我们来看一下文档中所说的事务等效项:

However, git checkout HEAD should never fail. Given that it won't actually fail, the transactional nature of the -B operation becomes unimportant. So now we look at what the documentation says this is the transactional-equivalent-of:

$ git branch -f <branch> [<start point>]
$ git checkout <branch>

我们知道起点是HEAD，所以:

We know that the start-point is HEAD, so:

git branch -f a_branch HEAD

是正确的:这与第一个命令匹配.而且，我们知道git checkout <the commit we are already on>本质上是无操作的(不会更改索引和工作树)，而git checkout a_branch最终会做:

is correct: this matches the first command. And, we know that git checkout <the commit we are already on> is essentially a no-op (does not change the index and work-tree) and git checkout a_branch ends up doing:

git symbolic-ref HEAD refs/heads/a_branch

作为其最终操作，因此:

as its final operation, so:

git checkout -B a_branch

手段":

1. 不对索引和工作树做任何事情(成功)；
2. 如果成功(执行此操作)，则将a_branch重置为当前提交；和
3. 如果成功(确实如此)，请使HEAD引用a_branch.

1. don't do anything to the index and work-tree (which succeeds);
2. if that succeeds (which it does), reset a_branch to the current commit; and
3. if that succeeds (which it does), make HEAD refer to a_branch.

但是，如果我们添加起点，则第1步可能会失败，而第2步(如果运行)可能会有所不同.

If we add the starting point, though, step 1 may fail, and step 2, if run, does something different.

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