[clue] arithmetic in bash

[David L. Willson]

Aaron,

Thanks for the well-thought-out answer. I'll return to using '$(( EXPRESSION ))', even though I can depend on bash for all my work.

I guess that '$[ EXPRESSION ]' has some capabilities over the old style, but I never do anything terribly complex.

In my specific application, getting some random numbers, '$(( EXPRESSION ))' is working perfectly.

Case in point:

# Generate a bunch of random looking numbers, in the range 1 to 10, inclusive.
while true ; do echo -n "$(( RANDOM % 10 + 1 )) " ; done

--
David L. Willson
Trainer, Engineer, Enthusiast
RHCE Network+ A+ Linux+ LPIC-1 Ubuntu
Mobile 720-333-LANS(5267)

This is a good time for a r3volution.

----- Original Message -----
> David L. Willson writes:
> > Why are the square brackets preferred (see below)? Why are there
> > two
> > forms?
> 
> I probably don't have this completely correct, but...  I'd say the
> recommendation is incorrect.
> 
> It is my understanding that the $(( ... )) syntax is a POSIX shell
> feature, while the $[ ... ] is something that bash added in the
> early-mid 1990s.  Given that, I try to use the $(( ... )) syntax
> exclusively.  The $[ .. ] syntax generally doesn't work on non-bash
> Bourne shells.  This may or may not be a concern for you.
> 
> Please stand by while I fire up the HP-UX box...
> 
> Here's what happens with $[ .. ] on a non-bash Bourne style shell:
> 
>     $ SHELL=/usr/bin/sh; exec $SHELL -o vi
>     $ uname -a
>     HP-UX billandd B.11.23 U 9000/800 1822910606 unlimited-user
>     license
>     $ echo $((2 * 5))
>     10
>     $ echo $[2 * 5]
>     $[2 fileset-cleanup 5]
>     $ exit
> 
> Compare with the results on a machine using bash:
> 
>     adj at sacredchao:~$ echo $SHELL
>     /bin/bash
>     adj at sacredchao:~$ uname -a
>     Linux sacredchao 3.2.0-0.bpo.1-amd64 #1 SMP Sat Feb 11 08:41:32
>     UTC 2012 x86_64 GNU/Linux
>     adj at sacredchao:~$ echo $((2 * 5))
>     10
>     adj at sacredchao:~$ echo $[2 * 5]
>     10
>     adj at sacredchao:~$
> 
> Googling for "bashism" will turn up many similar instances where Chet
> and crew added non-standard stuff to bash, and the efforts needed to
> weed them out when they're used in non-bash environments.
> 
> To sum up: I disagree with the recommendation in the Bash Guide for
> Beginners.  Use the POSIX syntax for arithmetic.  But if you can
> guarantee your scripts will run on nothing but bash, do whatever
> tickles your fancy.
> 
> - Aaron
> _______________________________________________
> clue mailing list: clue at cluedenver.org
> For information, account preferences, or to unsubscribe see:
> http://cluedenver.org/mailman/listinfo/clue
>