How about something like:

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

my %char_hash = ();
$char_hash{ chr($_) } = 0 foreach (33 .. 127);

while (<DATA>) {
    map $char_hash{$_}++, split //;
}
my @good_array = grep{ $char_hash{$_} == 0 } keys %char_hash;
print @good_array;

__DATA__
!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMOPQRSTUVWXYZ[\]^_`abcdefg
+hijklmnopqrstuvwxyz{|}~
[download]

where you may want to change the bounds on the first foreach loop.