[ale] simple math in bash

[Geoffrey Myers]

Chris Hamilton wrote:

> > > I can't remember how to do simple math in bash.  I used to know but I cant find
> >
> >       Don't know whether there is an easier way, but, I have always
> > used "dc" to do math in shell scripts. Ex, adding 1 + 1 would be:
> >
> > echo "1 1 + p q" | dc
>
> I either use bc (interactively) or expr.
>
>         E.g. $ expr 1 + 1

expr is a hog, using the foo=$((1 + 1)) is much faster.  A little benchmarking, first
ksh:

i=0;
time while [ $i -le 1000 ]; do
        i=`expr $i + 1`
done;print $i

1001
  32.47s real    0.89s user    2.29s system

i=0;
time while [ $i -le 1000 ]; do
        ((i=i + 1))
done;print $i
1001
   0.45s real    0.42s user    0.00s system

Some real major diffences.  This is ksh, but the tests under bash ( using the i=$((i
+ 1))  ) although not as impressive as ksh, they are substantial.  Same while loop:

i=`expr $i + 1`

14.36user 13.50system 0:35.38elapsed 78%CPU (0avgtext+0avgdata 0maxresident)k

i=$((i + 1))

8.65user 0.01system 0:09.28elapsed 93%CPU (0avgtext+0avgdata 0maxresident)k


So, if you're going to do math, better use ksh. :)


>
>
> Spang!
>
> ---
> Christopher Hamilton            Internal System Administrator
> chrish at ifsintl.com              IFS International, Inc.



--
Until later: Geoffrey           geof at abraxis.com