use strict;
use warnings;

my $string = 'A000 A123 A567 B789 B888 B999 B000 A998 A999';

my $regex = qr/((A|B)(\d{3}))/;
while  ( $string =~ /$regex/g ) {
  if ( $2 eq 'A' ) {
    if ( $3 == 000 or 
        ($3 >= 123 and $3 <= 456) or $3 == 999 ) {
    print "$1 valid string\n"; }
    else { print "$1 rejected invalid range\n" }
  }
  elsif ( $2 eq 'B' ) {
    if ( $3 == 000 or ($3 >= 789 and $3 <= 888) ) {
      print "$1 valid string\n"; 
    }
    else { print "$1 rejected invalid range\n" }
  }
  else { print "$3 seems valid to me\n" }
}