Doing a modulo in /bin/sh??

[Gary Kline]

On Wed, Aug 31, 2005 at 01:42:05PM -0500, Dan Nelson wrote:
> In the last episode (Aug 31), Gary Kline said:
> > 	I can grab the results of "w=$date+%U)"; in C an use the modulo
> > 	operator; is there a way to do this is /bin/sh?  ot zsh?
> > 
> > #/bin/sh
> > w=$(date +%U)
> > echo "w is $w";
> > (even=$(w % 2 ));       ## flubs.
> > echo "even is $even";       ## flubs.
> > 
> > if [ $even -eq 0 ]       ## flubs, obv'ly.
> > then
> >         echo "week is even";
> > else
> >         echo "week is odd";
> > fi
> 
> For the simple even/odd case, you can AND with 1:
> 
> even=$(( w & 1 ))
> 
> For the general case:
> 
> xmodn=$(( x - ((x / n) * n) ))


	I didn't think of the first cast, but yep; the general is 
	seriously sharp in my book; got to salt this away:-)  Thanks.
> 
> which works since sh's arithmetic evaluator is integer-only.
> 
> zsh has the % modulo operator, so xmod=$(( x % n )) .
> 

	I knew ksh/zsh/bash(?) have it; forgot about `expr`, tho.

	gary



-- 
   Gary Kline     kline at thought.org   www.thought.org     Public service Unix