ofcourse there are several ways of checking or testing primality of integers, I used Trial division method. There are other better method I believe. Check below:

use warnings;
use strict;

is_prime( $ARGV[0] );

sub is_prime {
    my ($val) = @_;
    my $num_sqrt = int( sqrt($val) );
    my @factor;
    for ( 2 .. $num_sqrt ) {
        if ( ( $val % $_ ) == 0 ) {
            push @factor, $_;
        }
    }
    my $count = () = @factor;
    print $val, " is a Prime Number" if $count == 0;
}
[download]

And 2 was used here because 1 is not a prime number by defination, which state that a prime number must have two factors: 1 and itself, but 1 has only itself! too bad for 1 though.
Also look into good advice given by tobyink under other suggestion on this post

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.