Date: Sun, 27 Jun 2010 11:20:15 +0400 From: Anonymous <swell.k@gmail.com> To: Giorgos Keramidas <keramida@ceid.upatras.gr> Cc: RW <rwmaillists@googlemail.com>, freebsd-questions@freebsd.org, Thomas Keusch <fwd@bsd-solutions-duesseldorf.de> Subject: Re: .sh check for numeric content Message-ID: <86mxuhuekw.fsf@gmail.com> In-Reply-To: <87fx0dvwfd.fsf@kobe.laptop> (Giorgos Keramidas's message of "Thu, 24 Jun 2010 08:20:22 %2B0300") References: <4C22B3D7.6070102@comclark.com> <20100624013755.GA5009@gothschlampen.com> <20100624034434.7a6c2895@gumby.homeunix.com> <20100624031953.GA21766@gothschlampen.com> <87fx0dvwfd.fsf@kobe.laptop>
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Giorgos Keramidas <keramida@ceid.upatras.gr> writes:
> On Thu, 24 Jun 2010 05:19:53 +0200, Thomas Keusch <fwd@bsd-solutions-duesseldorf.de> wrote:
>> tk@eternity:~$ b=5
>> tk@eternity:~$ case "$b" in
>>> [0-9] )
>>> echo numeric
>>> ;;
>>> * )
>>> echo alpha
>>> ;;
>>> esac
>> numeric
>> tk@eternity:~$
>>
>> 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.
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