use Parse::RecDescent;
use strict;
use warnings;

my $str = "ABC[GHI]XY[Z]1A";
my $grammar = <<'GRAMMAR';
  token : '[' /[A-Z]*/ ']' {$return = $item[2]}
           | /[A-Z]/
  anything : /./
GRAMMAR

my $parser = Parse::RecDescent->new($grammar);

# When a reference to a scalar is passed to Parse::RecDescent it will
# consume the tokens as they are matched. To avoid modifying the original
# string a copy will be used
my $copy = $str;
while ($copy ne '') {
    if (my $token = $parser->token(\$copy)) {
        print "Token: $token\n";
    }
    else {
        my $token = $parser->anything(\$copy);
        print "Invalid symbol: $token\n";
    }
}