a.pl

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

my $str = $ARGV[0] or die "usage: $0 <string>\n";

my $LOWER_BEGIN = ord('a');
my $LOWER_END = ord('z');
my $UPPER_BEGIN = ord('A');
my $UPPER_END = ord('Z');

my @char = split(//, $str);
for my $c (@char) {
    my $n = ord($c);
    if ($n >= $LOWER_BEGIN && $n <= $LOWER_END) {
        print lower_char();
    } else {
        print upper_char();
    }
}

sub lower_char {
    return chr(rand($LOWER_END - $LOWER_BEGIN) + $LOWER_BEGIN);
}

sub upper_char {
    return chr(rand($UPPER_END - $UPPER_BEGIN) + $UPPER_BEGIN);
}