jan@syrr:~$ perl -h
  -e program        one line of program (several -e's allowed, omit programfile)
  -i[extension]     edit <> files in place (makes backup if extension supplied)
  -p                assume loop like -n but print line also, like sed
  -n                assume "while (<>) { ... }" loop around program

my ($in, $out);
open($in, "<", "/etc/inittab") or die($!);
open($out, ">", "/etc/inittab.new") or die($!);
while(my $line = <$in>) {
    chomp $line;
    $line =~ s/remount,ro,noatime/remount,rw,noatime/g;
    print $out $line . "\n";
}
close($out);
close($in);

rename("/etc/inittab.new", "/etc/inittab");