no warnings 'qw'; # shut up Perl... I'm a big boy now!
my $chars = '';

vec($chars, ord $_, 1) = 1 for qw/! " # $ % & P Q R S T U V W X Y/;
# $chars is \x00 \x00 \x00 \x00 \x7e \x00 \x00 \x00 \x00 \x00 \xff \x03

$chars = pack 'u', $chars;
# $chars is ,`````'X``````/\#