use strict;
use warnings;

my @alphabet = ( '0' .. '9', 'a' .. 'z', 'A' .. 'Z' );
my $length = shift @ARGV || 8;

my $out = '';
while ( length $out  < $length ) {
    $out .= $alphabet[ rand @alphabet ];
}

print "$out\n";

##</code><code>##

perl -E '@a=("0".."9","A".."Z","a".."z");$o.=$a[rand@a]while 8>length$o;say$o'