my $filename = $ARGV[0];
my $nb_lines = 0;
open (my $file, $filename) or die "Can't open '$filename': $!";
my $hdl_sauv;
while (<$file>) {
    $nb_lines++ ;
    if ($nb_lines == 5) {
	open ($hdl_sauv, "<",$file) || die "cannot open $file\n";
    }
}

my $saved_line = <$hdl_sauv>;
print "$saved_line\n";