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From: Lars Schneider <larsxschneider@gmail.com>
To: Patrick Lehmann <Patrick.Lehmann@plc2.de>
Cc: Git Mailinglist <git@vger.kernel.org>,
	Stefan Beller <sbeller@google.com>
Subject: Re: Restoring detached HEADs after Git operations
Date: Mon, 19 Jun 2017 11:30:21 +0200	[thread overview]
Message-ID: <88AC6179-75D6-416B-9235-C628D6C59CA5@gmail.com> (raw)
In-Reply-To: <0092CDD27C5F9D418B0F3E9B5D05BE08010287DF@SBS2011.opfingen.plc2.de>


> On 19 Jun 2017, at 10:46, Patrick Lehmann <Patrick.Lehmann@plc2.de> wrote:
> 
> Hello,
> 
> I wrote a Bash script to recover branch names after Git operations have create detached HEADs in a Git repository containing lots of Git submodules. The script works recursively.

I did run into this situation myself and therefore
I understand your motivation. I've CC'ed Stefan as
he is a Submodule expert!


> I would like to see:
> a) that script or algorithm being integrated into Git by default
> b) that as a default behavior for all Git operations creating detached HEADs
> 
> That's the command:
> --------------------------------
> git submodule foreach --recursive  'HEAD=$(git branch --list | head -n 1); if [[ "$HEAD" == *HEAD* ]]; then REF=$(git rev-parse HEAD); FOUND=0; for Branch in $(git branch --list | grep "^  " | sed -e "s/  //" ); do if [[ "$(git rev-parse "$Branch")" == $REF ]]; then echo -e "  \e[36mCheckout $Branch...\e[0m"; git checkout $Branch; FOUND=1; break; fi done; if [[ $FOUND -eq 0 ]]; then echo -e "  \e[31mNo matching branch found.\e[0m"; fi else echo -e "  \e[36mNothing to do.\e[0m"; fi'
> --------------------------------
> 
> How does it work:
> 1. It uses git submodule foreach to dive into each Git submodule and execute a series of Bash commands.
> 2. It's reading the list of branches and checks if the submodule is in detached mode. The first line contains the string HEAD.
> 3. Retrieve the hash of the detached HEAD
> 4. Iterate all local branches and get their hashes
> 5. Compare the branch hashes with the detached HEAD's hash. If it matches do a checkout.

If there are multiple branches with the same hash then
your script would pick the first one. Can you imagine a
situation where this would be a problem?

Plus, you are looking only at local branches. Wouldn't it
make sense to look at remote branches, too?


> 6. Report if no branch name was found or if a HEAD was not in detached mode.
> 
> The Bash code with line breaks and indentation:
> --------------------------------
> HEAD=$(git branch --list | head -n 1)
> if [[ "$HEAD" == *HEAD* ]]; then
>  REF=$(git rev-parse HEAD)
>  FOUND=0
>  for Branch in $(git branch --list | grep "^  " | sed -e "s/  //" ); do

There is a convenient "git for-each-ref" function to iterate over
branches in scripts. See here an example:
https://github.com/larsxschneider/scotty/blob/master/admin/oss-fork.sh#L88


>    if [[ "$(git rev-parse "$Branch")" == $REF ]]; then
>      echo -e "  \e[36mCheckout $Branch...\e[0m"
>      git checkout $Branch
>      FOUND=1
>      break
>    fi
>  done
>  if [[ $FOUND -eq 0 ]]; then
>    echo -e "  \e[31mNo matching branch found.\e[0m"
>  fi
> else
>  echo -e "  \e[36mNothing to do.\e[0m"
> fi
> --------------------------------
> 
> Are their any chances to get it integrated into Git?
> 
> I tried to register that code as a Git alias, but git config complains about quote problem not showing where. It neither specifies if it's a single or double quote problem. Any advice on how to register that piece of code as an alias?

Try to escape ". See here for an example:
https://github.com/Autodesk/enterprise-config-for-git/blob/master/config.include#L76-L94


> If wished, I think I could expand the script to also recover hash values to Git tags if no branch was found.

It would be indeed nice to see the tagged version on my prompt.

--

Submodule processing is already quite slow if you have many of them.
I wonder how much this approach would affect the performance.

- Lars


  reply	other threads:[~2017-06-19  9:30 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-19  8:46 Restoring detached HEADs after Git operations Patrick Lehmann
2017-06-19  9:30 ` Lars Schneider [this message]
2017-06-19  9:52   ` AW: " Patrick Lehmann
2017-06-19 16:37     ` Stefan Beller
2017-06-19 17:34       ` AW: " Patrick Lehmann
2017-06-19 17:47         ` Stefan Beller
2017-06-19 18:09           ` AW: " Patrick Lehmann
2017-06-19 19:21             ` Stefan Beller
2017-06-19 20:13               ` AW: " Patrick Lehmann
2017-06-19 17:55       ` Junio C Hamano
2017-06-19 19:11         ` Stefan Beller
2017-06-19 16:31 ` Stefan Beller
2017-06-19 17:01 ` Jeff King
2017-06-19 17:56 ` Ævar Arnfjörð Bjarmason

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