.sh check for numeric content

[Anonymous]

Giorgos Keramidas <keramida at ceid.upatras.gr> writes:

> On Thu, 24 Jun 2010 05:19:53 +0200, Thomas Keusch <fwd at bsd-solutions-duesseldorf.de> wrote:
>> tk at eternity:~$ b=5
>> tk at eternity:~$ case "$b" in
>>> [0-9] )
>>>         echo numeric
>>>         ;;
>>> * )
>>>         echo alpha
>>>         ;;
>>> esac
>> numeric
>> tk at eternity:~$
>>
>> Works for me.
>
> Depending on what "numeric" means, this may be ok.  For other numeric
> values (e.g. floating point numbers) There are simple, fast and correct
> ways to check but you have to escape from the shell, e.g.:
>
>     $ var=3.1415926535897931
>     $ python -c "$var + 0.0" >/dev/null 2>&1 ; echo $?
>     0

      $ printf %g $var 2>&- >&- ; echo $?
      0

>
>     $ var=3a.1415926535897931
>     $ python -c "$var + 0.0" >/dev/null 2>&1 ; echo $?
>     1

      $ printf %g $var 2>&- >&- ; echo $?
      1

It also understands %e and %a -notation, e.g. 3.14e+2 and 0x1.3ap+8.

      $ python -c 0x1.3ap+8 2>&- >&- ; echo $?
      1
      $ printf %g 0x1.3ap+8 2>&- >&- ; echo $?
      0

>
> The overhead of spawning a full-blown language interpreter like Perl or
> Python may be acceptable if you have to check "a few" values.  Then it
> may be overkill if you want to check a million values.  It's really up
> to you, as a programmer, to pick the right method.

Besides, printf(1) is also builtin in some shells which can reduce
overhead of spawning process. IIRC, there is some support for builtin
printf in our /bin/sh but it's disabled.