On Thu, Jun 6, 2013 at 8:11 AM, Eric Blake <eblake@xxxxxxxxxx> wrote:
> ----- Original Message -----
>
>>
>> A more robust, (and more portable), formulation may be:
>>
>> echo $var | grep '^+\{0,1\}[0-9]\{1,\}$' > /dev/null 2>&1
>
> Why fork, when straight shell will do?
yea, forking for grep is probably going to make your script significantly slower
>
> case $var in
> +*) tmp=$var ;;
> *) tmp=+$var ;;
> esac
> case $tmp in
> +*[!0-9]* | +) echo "not numeric" ;;
> *) echo integer ;;
> esac
i've found through benchmarks that certain shells (dash and bash and
ksh) are optimized towards if statements over case ones
i would parse the number like this for best performance, but make a
copy for $var because it's destructive:
trim()
{
n=$1 v=$2
while [ ${#v} -ne $n ]
do
v=${v%?}
done
echo $v
}
if [ -z "$var" ]; then
echo "ENOTNUM $var" >&2
exit 2
fi
if [ $(trim 1 $var) = '+' ]; then
echo "we got a signed number; begin normalizing procedure"
var=${var#?}
fi
while [ ${#var} -ne 0 ]
do
if [ ${var%${var#?}} = '0' ] || [ ${var%${var#?}} = '1' ] || [
${var%${var#?}} = '2' ] || [ ${var%${var#?}} = '3' ]; then
echo "digit is base 4"
else
echo "ENOTNUM $var" >&2
exit 2
fi
var=${var#?}
done
>
> Again, when placing this in autoconf.ac, you need to quote the
> [0-9] since m4 eats one level of [], either by writing [[0-9]]
> in place, or by using [] around the entire case snippet.
>
> --
> Eric Blake eblake@xxxxxxxxxx +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
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