for ('23') {
  /2/ and process($0);
  /3/ and finalize();
}

##</code><code>##

Modification of a read-only value attempted at ./test.pl line 9.

##</code><code>##

for my $switch ($runlvl) {
  $switch =~ /2/ and process($0);
  $switch =~ /3/ and finalize();
}