If you want to avoid potential issues w/ regex metacharacters, you can use a set of hash keys to track what's been seen and rebuild the regex once for each character:
#!/usr/bin/perl
use strict;
use warnings;
my %char_hash = ();
$char_hash{ chr($_) } = undef foreach (33 .. 127);
my $chars = join "", keys %char_hash;
my $regex = "([\Q$chars\E])";
while (<DATA>) {
while (/$regex/g) {
delete $char_hash{$1};
$chars = join "", keys %char_hash;
$regex = "([\Q$chars\E])";
}
}
my @good_array = keys %char_hash;
print @good_array;
__DATA__
!"#$%&'()*+,-./01234567
89:;<=>?@ABCDE
FGHIJKLMOPQRSTUVWXYZ[\]^_`abcdefghijklmnop
qrstuvwxyz{|}~
though I feel like there must be a simpler way of implementing this approach.
