my $invalue = param( 'INVALUE' );
if ( defined $invalue ) {
    if ( $invalue =~ /\D/ ) {
        $result = "$invalue is *not* a Number@"
    } else {
        $result = "$invalue is a number.";
    }
} else {
    $result = "Enter a value to test."
}

##</code><code>##

$less->{'characters'}->{'typed'} == `"time in the pub" | more`; # :-D

##</code><code>##

/^(?:-)?\d+(?:\.\d+)?$/

##</code><code>##

/^(?:-)?(?:\d+(?:\.\d+)?|\.\d+)$/