git question: how do I get a specific git version into my working directory?

git question: how do I get a specific git version into my working directory?

[Alan Mackenzie]

Hello, Emacs.

A simple question (I hope):  How do I get a specific SW revision into my
working directory.  I want to do something like this:

   git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

.  git checkout doesn't seem to be the thing.  Neither does git revert.
What is <command> here?

-- 
Alan Mackenzie (Nuremberg, Germany).

Re: git question: how do I get a specific git version into my working directory?

[Andreas Schwab]

Alan Mackenzie <acm@muc.de> writes:

> A simple question (I hope):  How do I get a specific SW revision into my
> working directory.  I want to do something like this:
>
>    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
>
> .  git checkout doesn't seem to be the thing. 

Why do you think so?

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: git question: how do I get a specific git version into my working directory?

[Steinar Bang]

>>>>> Alan Mackenzie <acm@muc.de>:

> Hello, Emacs.
> A simple question (I hope):  How do I get a specific SW revision into my
> working directory.  I want to do something like this:

>    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

> git checkout doesn't seem to be the thing.

"git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.

What result do you get and what were you expecting?  Do you have any
uncommitted files it refuses to overwrite?  If so, try
 git stash
 git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
 git stash pop

(don't stash if you have staged files, I think you have uncovered a bug
there...)

> Neither does git revert.  What is <command> here?

The command is "checkout".

WARNING! Dangeous work-losing command ahead!
There is also
 git reset --hard 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
which will overwrite anything uncommitted and set your workstate to the
version described in 7e09ef09a479731d01b1ca46e94ddadd73ac98e3.

If you just want to apply that commit, do:
 git cherry-pick 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

Re: git question: how do I get a specific git version into my working directory?

[Eli Zaretskii]

> From: Steinar Bang <sb@dod.no>
> Date: Sat, 18 Apr 2015 14:18:59 +0200
> 
> >>>>> Alan Mackenzie <acm@muc.de>:
> 
> > Hello, Emacs.
> > A simple question (I hope):  How do I get a specific SW revision into my
> > working directory.  I want to do something like this:
> 
> >    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
> 
> > git checkout doesn't seem to be the thing.
> 
> "git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.

It also creates a "detached HEAD", so Alan should IMO be aware of
that, and return to the upstream head ASAP (or, better, do all of this
in a separate branch to begin with).

Re: git question: how do I get a specific git version into my working directory?

[Alan Mackenzie]

Hello, Eli.

On Sat, Apr 18, 2015 at 03:42:42PM +0300, Eli Zaretskii wrote:
> > From: Steinar Bang <sb@dod.no>
> > Date: Sat, 18 Apr 2015 14:18:59 +0200

> > >>>>> Alan Mackenzie <acm@muc.de>:

> > > Hello, Emacs.
> > > A simple question (I hope):  How do I get a specific SW revision into my
> > > working directory.  I want to do something like this:

> > >    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

> > > git checkout doesn't seem to be the thing.

> > "git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.

> It also creates a "detached HEAD", so Alan should IMO be aware of
> that, and return to the upstream head ASAP (or, better, do all of this
> in a separate branch to begin with).

I'm aware of it, now!  Given that I'm not intending to do any VCS
operation on this, other than "git checkout <revision number>", I should
be all right, surely?  I'm expecting (?hoping) that on switching back to
the HEAD revision, the detached head (?all detached heads) will vanish.

-- 
Alan Mackenzie (Nuremberg, Germany).

Re: git question: how do I get a specific git version into my working directory?

[Dmitry Gutov]

On 04/18/2015 04:16 PM, Alan Mackenzie wrote:

> I'm aware of it, now!  Given that I'm not intending to do any VCS
> operation on this, other than "git checkout <revision number>", I should
> be all right, surely?  I'm expecting (?hoping) that on switching back to
> the HEAD revision, the detached head (?all detached heads) will vanish.

You'll have to switch back to a specific branch. Switching to HEAD is a 
no-op.

Re: git question: how do I get a specific git version into my working directory?

[Eli Zaretskii]

> Date: Sat, 18 Apr 2015 13:16:07 +0000
> From: Alan Mackenzie <acm@muc.de>
> Cc: emacs-devel@gnu.org
> 
> > > "git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.
> 
> > It also creates a "detached HEAD", so Alan should IMO be aware of
> > that, and return to the upstream head ASAP (or, better, do all of this
> > in a separate branch to begin with).
> 
> I'm aware of it, now!  Given that I'm not intending to do any VCS
> operation on this, other than "git checkout <revision number>", I should
> be all right, surely?  I'm expecting (?hoping) that on switching back to
> the HEAD revision, the detached head (?all detached heads) will vanish.

If I were you, I'd do all this in a separate branch, just to be sure
my 'master' branch had no chance whatsoever to be affected.  Then you
could simply delete that branch when no longer needed.

Re: git question: how do I get a specific git version into my working directory?

[Harald Hanche-Olsen]

Eli Zaretskii wrote:
> If I were you, I'd do all this in a separate branch, just to be sure
> my 'master' branch had no chance whatsoever to be affected.  Then you
> could simply delete that branch when no longer needed.

Since the master branch is just a pointer into some specific commit, I 
don't think anything you do while in a headless commit can affect the 
master branch in any way. (Unless, of course, you run commands that 
specifically name the master branch in order to change it.)

To get to the master branch just as it was, run “git checkout master”.

If you made changes while in the headless commit, that will fail. In 
which case, either abandon the changes with “git checkout -f master”, or 
stash them first.

– Harald

Re: git question: how do I get a specific git version into my working directory?

[Eli Zaretskii]

> Date: Sat, 18 Apr 2015 16:07:44 +0200
> From: Harald Hanche-Olsen <hanche@math.ntnu.no>
> Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
> 
> Eli Zaretskii wrote:
> > If I were you, I'd do all this in a separate branch, just to be sure
> > my 'master' branch had no chance whatsoever to be affected.  Then you
> > could simply delete that branch when no longer needed.
> 
> Since the master branch is just a pointer into some specific commit, I 
> don't think anything you do while in a headless commit can affect the 
> master branch in any way. (Unless, of course, you run commands that 
> specifically name the master branch in order to change it.)
> 
> To get to the master branch just as it was, run “git checkout master”.
> 
> If you made changes while in the headless commit, that will fail. In 
> which case, either abandon the changes with “git checkout -f master”, or 
> stash them first.

Yes, I know all that.  But I'd still do all that on a separate branch,
since 'master' is not supposed to be used for such stuff, it's
supposed to track upstream as close as possible.

Better be safe than sorry.

Re: git question: how do I get a specific git version into my working directory?

[Stefan Monnier]

> Yes, I know all that.  But I'd still do all that on a separate branch,
> since 'master' is not supposed to be used for such stuff, it's
> supposed to track upstream as close as possible.

I think Harald's point is that after "git checkout e56ab7" you're simply
not in "master" any more.  At least, not more than you're in any
other branch.  Instead, you're in a kind of transient nameless branch.


        Stefan

Re: git question: how do I get a specific git version into my working directory?

[Eli Zaretskii]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Date: Sat, 18 Apr 2015 13:09:01 -0400
> Cc: acm@muc.de, Harald Hanche-Olsen <hanche@math.ntnu.no>, emacs-devel@gnu.org
> 
> > Yes, I know all that.  But I'd still do all that on a separate branch,
> > since 'master' is not supposed to be used for such stuff, it's
> > supposed to track upstream as close as possible.
> 
> I think Harald's point is that after "git checkout e56ab7" you're simply
> not in "master" any more.  At least, not more than you're in any
> other branch.  Instead, you're in a kind of transient nameless branch.

And my point is: why have a nameless branch, if you can have a named
one?

Re: git question: how do I get a specific git version into my working directory?

[Harald Hanche-Olsen]

Eli Zaretskii wrote:
>> From: Stefan Monnier<monnier@IRO.UMontreal.CA>
>> Date: Sat, 18 Apr 2015 13:09:01 -0400
>> Cc: acm@muc.de, Harald Hanche-Olsen<hanche@math.ntnu.no>, emacs-devel@gnu.org
>>
>>> Yes, I know all that.  But I'd still do all that on a separate branch,
>>> since 'master' is not supposed to be used for such stuff, it's
>>> supposed to track upstream as close as possible.
>> I think Harald's point is that after "git checkout e56ab7" you're simply
>> not in "master" any more.  At least, not more than you're in any
>> other branch.

That's my point, yes.

 >> Instead, you're in a kind of transient nameless branch.

Well, not even that. Branches by definition have names: A branch is a 
name which (a) points to a commit, (b) moves to a newly created commit 
when you check in code, and optionally (c) has remote-tracking behaviour.

> And my point is: why have a nameless branch, if you can have a named
> one?

That's a good point, but the reason for it is not any danger of messing 
up the master branch. Rather, it is the danger of messing up any code 
you write while in the detached state.

– Harald

Re: git question: how do I get a specific git version into my working directory?

[Eric Abrahamsen]

Steinar Bang <sb@dod.no> writes:

>>>>>> Alan Mackenzie <acm@muc.de>:
>
>> Hello, Emacs.
>> A simple question (I hope):  How do I get a specific SW revision into my
>> working directory.  I want to do something like this:
>
>>    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
>
>> git checkout doesn't seem to be the thing.
>
> "git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.
>
> What result do you get and what were you expecting?  Do you have any
> uncommitted files it refuses to overwrite?  If so, try
>  git stash
>  git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
>  git stash pop
>
> (don't stash if you have staged files, I think you have uncovered a bug
> there...)
>
>> Neither does git revert.  What is <command> here?
>
> The command is "checkout".
>
> WARNING! Dangeous work-losing command ahead!
> There is also
>  git reset --hard 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
> which will overwrite anything uncommitted and set your workstate to the
> version described in 7e09ef09a479731d01b1ca46e94ddadd73ac98e3.
>
> If you just want to apply that commit, do:
>  git cherry-pick 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

I think the recommended approach is to create a branch pointing at a
specific commit. So:

git checkout -b test_branch 7e09ef09

Otherwise you're in a "detached head" state, which can have odd results.
The branch method is at least a little more stable.

Eric

Re: git question: how do I get a specific git version into my working directory?

[Alan Mackenzie]

Hello, Steinar.

On Sat, Apr 18, 2015 at 02:18:59PM +0200, Steinar Bang wrote:
> >>>>> Alan Mackenzie <acm@muc.de>:

> > Hello, Emacs.
> > A simple question (I hope):  How do I get a specific SW revision into my
> > working directory.  I want to do something like this:

> >    git <command> 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

> > git checkout doesn't seem to be the thing.

> "git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3" should work.

> What result do you get and what were you expecting?  Do you have any
> uncommitted files it refuses to overwrite?  If so, try
>  git stash
>  git checkout 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
>  git stash pop

> (don't stash if you have staged files, I think you have uncovered a bug
> there...)

No, I hadn't tried the command.  I have now, and it "seems to work".

> > Neither does git revert.  What is <command> here?

> The command is "checkout".

Thanks!

> WARNING! Dangeous work-losing command ahead!
> There is also
>  git reset --hard 7e09ef09a479731d01b1ca46e94ddadd73ac98e3
> which will overwrite anything uncommitted and set your workstate to the
> version described in 7e09ef09a479731d01b1ca46e94ddadd73ac98e3.

> If you just want to apply that commit, do:
>  git cherry-pick 7e09ef09a479731d01b1ca46e94ddadd73ac98e3

I am doing a bisect: a bisect where I only want revisions taken into
account when specific files have been modified.

-- 
Alan Mackenzie (Nuremberg, Germany).

Re: git question: how do I get a specific git version into my working directory?

[Dmitry Gutov]

On 04/18/2015 04:09 PM, Alan Mackenzie wrote:

> I am doing a bisect: a bisect where I only want revisions taken into
> account when specific files have been modified.

Have you tried passing those file paths after "git bisect start --"?

http://stackoverflow.com/questions/3179498/how-can-i-cut-down-a-git-bisect-run-using-file-paths

Re: git question: how do I get a specific git version into my working directory?

[Steinar Bang]

>>>>> Alan Mackenzie <acm@muc.de>:

> I am doing a bisect: a bisect where I only want revisions taken into
> account when specific files have been modified.

Hm... when I do bisect I just to "git bisect" and feed it the two sha1
hashes it should bisect between, and it has so far done its magic to my
satisfaction (ie. if it was caused by a commit, I have successfully
identified a particular commit where the issue starts).

After that I usually branch off from the commit before the offending
commit and stay there until things are resolved (unless I'm able to
resolve it myself).

Or I branch off master and revert the offending commit until things are
resolved, ie. like so
 git checkout master
 git checkout -b sb-master
 git revert sha1-of-offending-commit

(that's what I did with gnus, when cram-md5 auth disappeared from nnimap
with SSL/TLS...)

Re: git question: how do I get a specific git version into my working directory?

[Andreas Schwab]

Alan Mackenzie <acm@muc.de> writes:

> I am doing a bisect: a bisect where I only want revisions taken into
> account when specific files have been modified.

A typical XY problem.

http://www.perlmonks.org/?node=542341

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."