McEs, A Hacker Life: bash

Tuesday, February 07, 2006

bash_completion...

Now I've been in love with the bash_completion package for a couple years now. I've always wondered about how much performance hit does it cause, by loading all the completion rules for all commands known to it in every bash shell, which is default shell in any decent Linux system, every single time... But never measured before.

Tonight, I'm writing a shell script (will post soon), and I was wondering why does it take 0.66s for it to print out usage information. Indeed it was bash_completion. First disable it, time down to 0.09s. Neat. But then I simply added a single magic line to /etc/profile.d/bash_completion.sh:

[ -z "$PS1" ] && return

so it doesn't run in non-interactive shells. That's it!

¶ 3:35 AM

Comments:

[[ $- = *i* ]] && return

Does the same thing and works in sh, ksh, bash

# posted by

Anonymous : February 07, 2006 7:56 AM

I don't think that portability to non-bash shells is an issue with bash_completion.sh ;-)

# posted by

Anonymous : February 07, 2006 8:20 AM

Mandriva uses:

if [ "$PS1" ] && [ -n "$BASH" ]; then
# source user config file if available,
# otherwise system wide config file
if [ -f $HOME/.bash_completion ]; then
. $HOME/.bash_completion
else
. /etc/sysconfig/bash-completion
fi

if [ -n "$ENABLE_BASH_COMPLETION" ]; then
. /etc/bash_completion
fi
fi

Is there any difference with your approach?
I think both don't run in non-interactive shells. Which distribution are you using?

# posted by

Anonymous : February 07, 2006 9:02 AM

I just thought I'd take this time to mention zsh if you've got a passion for autocompletion in general.

Amongst loads of other things, it offers pretty intelligent and advanced autocompletion for just about anything with the proper config. (But then again, it does handle a lot with autocompletion simply enabled and without any explicit rules set, too.)

anonymous@huh:~% gcc -*TAB*
-A -ansi -fshort-enums
-B -b -fsigned-bitfields
-C -c -fsigned-char
-D -d -fstrength-reduce
-E -fPIC -fstrict-prototype
-H -fall-virtual -fsyntax-only

..etc.

Similar rules for host completion, amongst other things can be added as I'm sure you may already be aware of with bash.

http://docs.cs.byu.edu/docs/zsh/ might be a good place to start if you're interested.

Cheers.

# posted by

Anonymous : February 07, 2006 11:25 AM

Thanks for all the comments. I'm using Fedora. Reported this bug:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=180419

# posted by

behdad : February 07, 2006 8:22 PM

Thanks for pointing this out. bash completion used to have code to guard against this, but it seems to have accidentally been removed quite a while back.

The next release will have this check reinstated.

# posted by

Anonymous : February 23, 2006 11:19 AM

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