Re: git-PS1 bash prompt setting

From: Shawn Pearce <spearce@spearce.org>
Date: Nov 27, 2006, 17:02 UTC
Message-ID: <20061127170249.GC6616@spearce.org>
In-Reply-To: <20061127075650.81a5a850.seanlkml@sympatico.ca>

Sean <seanlkml@sympatico.ca> wrote:

Show 18 quoted lines

> On Mon, 27 Nov 2006 01:54:00 -0500
> Shawn Pearce <spearce@spearce.org> wrote:
> 
> > I'm using something like this, and will be adding it to
> > git-completion.bash tonight:
> > 
> > 	__git_ps1 ()
> > 	{
> > 		local b="$(git symbolic-ref HEAD 2>/dev/null)"
> > 		if [ -n "$b" ]; then echo "(${b##refs/heads/})"; fi
> > 	}
> > 	PS1='[\u@\h \W$(__git_ps1)]\$ '
> > 
> > it works very well...
> 
> Yeah, when I first coded it I even looked at making it a bash loadable
> to make it perform better but found the prototype to run acceptably,
> so never bothered.

When I originally coded the first version of __git_ps1 I was using it on a Cygwin system, where the fork+exec of the external script can take a little while. The time to fork+exec two programs (script and then git) is huge compared to just fork+exec of git by itself, so I coded it as a function. On the other hand my Mac OS X system doesn't even blink at either implementation.

> If Git does get a --show-ps1 option, people will
> still be able to roll their own version to tweak the output format
> as you did above.  Hopefully the standard format will work for most
> though.

I'm not sure that's worth implementing in the core code. Most shells that will let you invoke a command as part of their prompt generation will also let you use builtin functions and do some basic string manipulation (e.g. like I do above with bash). At which point it is say 5 lines of shell (nicely formatted) to craft a prompt string vs. 15-20 lines of C to parse the option, read HEAD, and craft a prompt string.

If someone else contributes a --show-ps1 option that is useable as a replacement for my __git_ps1 I'll gladly jump on board and change to using it, but I just don't see a reason to write it myself.