#use whateveryouwant;
my $filename = "insertfilenamehere";
open INPUT, $filename or die;
my $modify_state = "false";
my $line = "";
while ($line = <INPUT>)
{
  chomp($line);
  #look for the value
  if ($line =~ /are these the droids you're looking for?/)
  {
     $modify_state = "true";
     last;
  }
}
close INPUT;
if ($modify_state eq "false")
{
  open INPUT, $filename;
  open OUTPUT, ">output" or die;
  while ($line = <INPUT>)
  {
     #modify the line here

     #and print to the output file 
  }
  close OUTPUT;
  close INPUT;
  #rename the output file back to the original filename.
}