substr $string, 0, 30; 
  # will extract UP TO the first 30 characters of the string.

$string =~ m/(.{30})/; 
  # will extract the first 30 characters, if the string is AT LEAST 30 characters long

$string =~ m/.{30}/; 
  # tests if the string is AT LEAST 30 characters long

length($string) == 30;
  # tests if the string is 30 characters long.