Subject: Re: What does git reset do?

From: Jakub Narebski <[email-masked]>
Date: Tue, 02 Feb 2010 07:30:11 -0800 (PST)

Ron Garret <[email-masked]> writes:

> The docs say that git-reset:
> 
> "Sets the current head to the specified commit..."
> 
> So I tried this:
> 
> 
> [ron@mickey:~/devel/gittest]$ git branch
> * br1
>   master
> [ron@mickey:~/devel/gittest]$ git reset --soft master
> 
> 
> ...expecting HEAD to now point to master.  But it doesn't:

First, 'current head' is what HEAD points to, which means 'br1'
branch.

Second, "git reset --soft master" sets 'br1' branch to _commit_
'master' (commit referenced by 'master' branch).

> 
> 
> [ron@mickey:~/devel/gittest]$ git branch
> * br1
>   master
> [ron@mickey:~/devel/gittest]$ more .git/HEAD 
> ref: refs/heads/br1
> 
> 
> So... what does git reset do?

Let's assume that we have the following situation:

                /-*        <-- branch_A
               /
  *---*---*---*---*---*    <-- branch_B  <--- HEAD

1. $ git checkout branch_A

sets HEAD to branch_A, and sets index and working directory:

                /-*        <-- branch_A  <--- HEAD
               /
  *---*---*---*---*---*    <-- branch_B

2. $ git reset --hard HEAD

sets current branch to commit pointer by branch_A (--soft, --mixed,
--hard), and sets index (--hard and --mixed) and working directory
(--hard):

                   /---------- branch_B  <--- HEAD
                  v

                /-*        <-- branch_A
               /
  *---*---*---*---*---*    

..................................................

Let's assume that we have the following situation:

  *---*---*---a---b---c    <-- branch_A  <--- HEAD
              ^
              |
            v1.0 (tag)

3. $ git checkout v1.0

detaches HEAD:

                /-b---c    <-- branch_A
               /
  *---*---*---a            <--- HEAD
              ^
              |
            v1.0 (tag)

4. $ git reset --hard v1.0

rewinds current branch:

                /-b---c    
               /
  *---*---*---a            <-- branch_A <--- HEAD
              ^
              |
            v1.0 (tag)

Note that commit 'c' might be referenced only by ORIG_HEAD, HEAD@{1}
(reflog for HEAD), and branch_A@{1} (reflog for branch_A); if it is
the case commits 'b' and 'c' would get garbage-collected and removed
eventually.

HTH
-- 
Jakub Narebski
Poland
ShadeHawk on #git