my $line = 'fee fi fo fum';
my $pat = qr/i smell the blood/;
unless( grep /$pat/, $line ){
    print "of an englishman\n";
}
__END__

##</code><code>##

unless( $line =~ /$pat/ ) { ...
if( not $line =~ /$pat/ ) { ...
if( $line !~ /$pat/ ) { ...