open(READ, $filer) || die "error: couldnt open file: $!";
open(WRITE, "> $filew") || die "error: couldnt open file: $!";

while (defined ($line = <READ>))
{
@words = split(/ /, $line);

#here id like to compare word from each line of "input" with "cetnosti" and write it to "output" but i have no idea how to do it

}
close(READ);
close(WRITE);