my $input = 'http://www.knowmad.com/';
my $constraint_good = '/[\\!@#%&_:\$\^\*\(\)\+\.\/]+/';
my $constraint_bad = '/[!@#%&_:\$\^\*\(\)\+\.\/]+\\/';


if ( $constraint_good =~ m@^\s*(/.+/|m(.).+\2)[cgimosx]*\s*$@ ) {
	my $sub = eval 'sub { $_[0] =~ '. $constraint_good .  '}';
		die "Error compiling regular expression $constraint_good: $@" if
			$@;
		print "matched\n";
} else {
	print "no good.\n"
}

if ( $constraint_bad =~ m@^\s*(/.+/|m(.).+\2)[cgimosx]*\s*$@ ) {
	my $sub = eval 'sub { $_[0] =~ '. $constraint_bad .  '}';
		die "Error compiling regular expression $constraint_bad:
			$@" if $@;
		print "matched\n";
} else {
	print "no good.\n"
}