my $exceptions = qr/_ALPHA|#ALPHA|XL5 ALPHA/;
my $keepers = qr/ALPHA|BETA/;
while (my $srch = <DATA>) {
  print "Matched ($srch)!\n" unless $srch=~/^(?:$exceptions|(?!$keepers).)*$/;
}
__DATA__
one with #ALPHA and good ALPHA
one with just XL5 ALPHA
one with just BETA
one with _ALPHA and BETA