Date: Fri, 1 Oct 2004 12:56:14 +0400 From: "Andrew" <infofarmer@mail.ru> Cc: <freebsd-questions@freebsd.org> Subject: Re: 64-bit arithmetic in scripts? Message-ID: <001501c4a794$81d031c0$4611a8c0@SATPC> References: <000601c4a720$99264270$4611a8c0@SATPC> <20040930194001.GD22530@dan.emsphone.com> <004901c4a729$61fc7810$4611a8c0@SATPC> <20040930204808.GE22530@dan.emsphone.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Dan Nelson has kindly explained everything:
> In the last episode (Oct 01), Andrew said:
> > Thanks! I haven't thought about using expr.
> >
> > How come that my expr(1) manpage has nothing to say about -e option?
> > In fact my expr(1) does not accept it. I have FreeBSD 4.10. I've
just
> > looked into a current manpage from www.freebsd.org, and it says
> > something about 4.x compatibility.
> >
> > What is the best way to go if I need to write scripts now, but I'm
> > planning to switch to 5.x later? Can I upgrade expr(1) now? If not,
> > what should I do?
>
> In 4.x, expr does 64-bit math by default. Apparently POSIX requires
> that expr use whatever the systems' "signed long" size is, so the
> default was changed for 5.x, and -e was added to get the old
behaviour.
>
> If you want your script to work on both, you'll have to do a feature
> test. I started out just testing expr and expr -e, but it sort of
> grew... The following script will check the shell's math, two ways of
> calling expr, and finally fall back on calling bc. As long as you
just
> use the basic math operators, quote your "*"'s, and put spaces between
> everything, all the methods should be compatible, and your script will
> work on any bourne-compatible shell :)
>
> #! /bin/sh
>
> if [ x$(( 65536 * 65536 )) = "x4294967296" ] ; then
> shellarith() { echo $(( $@ )) ; }
> MATH="shellarith"
> else
> if [ x`expr 65536 "*" 65536` = "x4294967296" ] ; then
> MATH="expr"
> else
> if [ x`expr -e 65536 "*" 65536 2>/dev/null` = x"4294967296" ] ;
then
> MATH="expr -e"
> else
> if [ x`echo 65536 "*" 65536 | bc` = "x4294967296" ] ; then
> bcfunc() { echo "$@" | bc ; }
> MATH="bcfunc"
> else
> echo "Can't do 64-bit math noway nohow"
> fi
> fi
> fi
> fi
>
> echo "Using $MATH"
> bigval=`$MATH 65536 "*" 65536`
> echo $bigval
Thank you very much! I think, I'll just assign MATH="expr" and change it
to something else when I need it.
Best regards,
Andrew P.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?001501c4a794$81d031c0$4611a8c0>