Lowercase that \S, this will result in a negated character class containing an 'A' and whitespace (as defined by \s) e.g

my $cc = qr/^[^A\s]+$/;

print "foo" =~ $cc ? "yep" : "nope";
print "foA" =~ $cc ? "yep" : "nope";
print "fo " =~ $cc ? "yep" : "nope";

__output__

yep
nope
nope
[download]

See. perlre for more info.
HTH

_________
broquaint