Let's see if I got the requirements down:

• Command line encrypter [sic]
• Encrypt it with no problem

Given that the OP's requirements did not specify that the resultant output of the command line encrypter must be able to be interpreted, I present...

#!/usr/bin/perl
use strict;
use warnings;

my ($final, $rot);

$_ = shift;

open (INFILE, $_) || die "Can't open $_: $!";

while (<INFILE>) {
    foreach (split //) {
        if (/[a-m]/i) {
            $rot = 13;
        } elsif (/[n-z]/i) {
            $rot = -13;
        } else {
            $rot = 0;
        }
        $final .= chr(ord() + $rot);
    }
}
close(INFILE);

print $final;
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Cē