http://www.perlmonks.org?node_id=422406

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#!/usr/bin/perl -w
# prime.pl, v2.0 - test for primality
#  thanks to: mr_mischief for help and efficient isPrime() rewrite.
#  also: i prefer the code TedPride uses in node 430254 to find the
#  highest divisor, so i have modified my own here..

use strict;
use warnings;

@ARGV or die &usage;

print "\n[RESULTS]\n\n";

foreach my $num (@ARGV) { isPrime($num); }

sub isPrime {
    my $num = $_[0];
    my $val = 'prime';
    if ($num =~ /^\d+$/ && $num >= 2) {
        my $mod = 2;
        my $div = int sqrt $num;
        while ($mod <= $div) {
            ($num % $mod) == 0 ? ($val = 'composite', last) : $mod++;
        }
    } else { $val = 'neither'; }
    print ' ' . $num . ":\t\t$val\n";
}

sub usage {
    print "\nUsage: " . $0 . " <number(s)>\n";
    print "\n\tOnly real, whole numbers greater than one can be prime.
+\n";
    exit 1;
}

# rz/021005
[download]

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