open (IN,"<$myfile") or die "open failed for read: $!";
my @lines = <IN>;
close (IN);

open (OUT, ">$myfile") or die "open failed for write: $!";
foreach (@lines) {
  chomp;
  my ($user,$pass) = split(/=/);
  # Check username
  if ($user eq $i_user) {
    # Check password
    if ($pass eq $i_pass) {
      # Check the confirmation of the new password
      if ($i_newpass eq $i_cnewpass) {
        print OUT "$user=$i_newpass\n";
      }
    }
  }
  else {
    print OUT "$user=$pass\n";
  }
}
close (IN);