print "Match1\n" if "aa1" =~ /^(a)\1(#)1$/;  # comment not works
print "Match2\n" if "aa1" =~ /^(a)\1.{0}1$/; # works, but it's very ugly
print "Match3\n" if "aa1" =~ /^(a)\1 1$/x;   # works, but I don't want to use x modifier...
print "Match4\n" if "aa1" =~ /^(a)\g{1}1$/;  # works, but since Perl 5.10...