I agree with the other monks that the module is the best solution if you want to know if perl considers your string a number. But I will try to answer your original question. It is actually better to only test for the valid cases, and assume that it is invalid otherwise. The following code is a simplified version of yours.

use strict;
use warnings;
use Test::Simple tests => 10;

sub IsNumber
{
    (local $_) = @_;
    return (m/^[+-]?\d+$/ or m/^[+-]?[0-9]+[.]?[0-9]+$/) ;
}

ok( !IsNumber("0777 891 777"));
ok(  IsNumber("1.5671") );
ok( !IsNumber("121A3D") );
ok(  IsNumber("777") );
ok(  IsNumber("0") );
ok(  IsNumber("-4.567") );
ok( !IsNumber("+9.8.97") );
ok(  IsNumber("+9.897") );
ok( !IsNumber("+9.8¬97") );
ok( !IsNumber("9.8[97") );
[download]

OUTPUT:

1..10
ok 1
ok 2
ok 3
ok 4
ok 5
ok 6
ok 7
ok 8
ok 9
ok 10
[download]