for my $file_no (1 .. 50) {
    my $filetag = "1AC$file_no";
    open my $fh, '>', "$filetag.mol" or die "Open fail for $filetag: $!";
    my @lines = generate_lines($file_no);
    for my $line (@lines) {
        print "$filetag $line\n";
    }
}