Perl's empty parentheses () idiom, is a list assignment in scalar context which returns the number of elements on the right-hand side of the list assignment.
() is very useful to count the number of matches in a regular expression
For example:
{code}
my $str = 'aa bb cccc';
my $val = () = $str =~ /\w+/g;
print $val;
{/code}
The above snippet will print number of matches in the regexp.