$toto = "tutu";
$tata = "titi";

$file = "/home/logarno/toto";
open(CANONICAL, "< $file");
while (<CANONICAL>) {
    if (/\@$toto\s*\@$tata/){
	goto NOUPDATE; 
    }
}
close(CANONICAL);
open(CANONICAL, ">> $file");
print CANONICAL "\n\@$toto \@$tata";
 NOUPDATE:
    close(CANONICAL);