Perl Wordlist Generator

#! /usr/bin/perl

use warnings;

print "How many characters to use: ";
chomp($how_many = <STDIN>);

print "Which characters to use: ";
chomp($characters = <STDIN>);

print "Enter filename to save to:";
chomp($filename = <STDIN>);

open $fh, '>', $filename;

sub doIt {
    my $i;
    if($_[1] eq 0) {
        print $fh $_[0]."\n";
    }
    else {
        for($i=0; $i le length($characters)-1; $i++) {
            doIt($_[0].substr($characters, $i, 1), $_[1]-1);
        }
    }
}

doIt("", $how_many);

close($fh);