Moose has type validation but I have never tried to use it stand alone. I did find the Data::Types module useful.

#!/usr/bin/perl
use warnings;
use strict;
use Data::Types qw(is_int);

foreach ( qw( 1.1 -2 0 3 hi 0.0 2e5 0b11 ), 0b11 ){
    print $_, (is_int($_) and $_>0) ? ' is':' is not', " a positive in
+teger.\n";
}

__DATA__
1.1 is not a positive integer.
-2 is not a positive integer.
0 is not a positive integer.
3 is a positive integer.
hi is not a positive integer.
0.0 is not a positive integer.
2e5 is not a positive integer.
0b11 is not a positive integer.
3 is a positive integer.
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