What does git reset do?

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:

[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?

Thanks, rg

On Mon, 01 Feb 2010 23:47:56 -0800, Ron Garret <ron1@flownet.com> wrote:

... without modifying your working copy if --soft, and modifying your working copy if --hard.

... and without switching branches (you want git checkout for that).

It actually does. HEAD (and br1) now point to [the commit pointed to by] master. Your working copy was left intact (because of --soft). Compare with "git checkout".

gitk --all is your friend to better understand this.

Your branch is still br1. It means, if you commit, br1 will advance, (not master). But, given your git reset, instead of committing over [the commit pointed to by previous] br1, you will commit over [the commit pointed to by] master.

Be careful though, you might lose commits with git reset.

Sets the current head (and branch, if not detached) to the specified commit...

In article <op.u7hpv8nd4oyyg1@localhost.localdomain>,
 "Octavio Alvarez" <alvarezp@alvarezp.ods.org> wrote:

Ah.  It's the "and branch" part that I was missing.  Thanks!

Hm... maybe "detached head" is not as inappropriate a term as I first thought. When you checkout a branch, HEAD really is "attached" to the branch insofar as the branch head gets "dragged along" on commits and resets. (Have I got that right?)

rg

On Tue, 02 Feb 2010 00:24:26 -0800, Ron Garret <ron1@flownet.com> wrote:

99% right. I'm just not sure if there is such thing as "branch head".

You may compare the branch with a "moving tag", in which case the branch is just a pointer, so "branch head" would be redundant, and besides "HEAD" is an already used term. So you may say simply "branch" instead.

But it's easy intuitive to compare it with a bunch of related commits, each parent of another. And gitk also has a line that says "branch: _____, ______, ______" for each commit.

In any case, it's just a matter of getting the terms to match the developers'.

Ron Garret <ron1@flownet.com> writes:

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).

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