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.
##</code><code>##

my @strings = (
  join ('', 'a' .. 'z' ),
  join ('', 'a' .. 'z', 0 .. 3 ),
  join ('', 'a' .. 'z', 0 .. 9 ),
);
foreach my $string (@strings) {
  print "\nstring : $string\n";
  print 'length : ', length($string), "\n";
  print 'substr : ', substr( $string, 0, 30 ), "\n";
  print 'regex  : ', ( $string =~ m/.{30}/ ), "\n";
  print 'regex  : ', ( $string =~ m/(.{30})/ ), "\n";
}
##</code><code>##

string : abcdefghijklmnopqrstuvwxyz
length : 26
substr : abcdefghijklmnopqrstuvwxyz
regex  : 
regex  : 

string : abcdefghijklmnopqrstuvwxyz0123
length : 30
substr : abcdefghijklmnopqrstuvwxyz0123
regex  : 1
regex  : abcdefghijklmnopqrstuvwxyz0123

string : abcdefghijklmnopqrstuvwxyz0123456789
length : 36
substr : abcdefghijklmnopqrstuvwxyz0123
regex  : 1
regex  : abcdefghijklmnopqrstuvwxyz0123