if (1) # extra if resets $1 backreference
{
  $filename =~ /^([^_]+)_([^_]+)/;
  $rs[0] = $1;
  $rs[1] = $2;
} # end of extra if (1)
open (TESTF, "<./$filename") or die "open\n";
# now process lines which may or may not have matches
while (my $line = <TESTF>)
{
  chomp $line;
  if ($line =~ /^\x7CTARGET/)
  {
     my ( $kw, $dtarget, $kw2, $dorient ) =
          split( /\x7C/, $line );
     $dorient =~ /^([^_]+)_/;
     $rs[2] = $1;
     if (!defined($rs[2])) { $rs[2] = 'nocount'; }
  }
  elsif (...)
  {
    ...
  }
}
# test @rs values