my $last_line;
for my $fname ( 'tax.pl', 'accno.pl', 'ptax.pl' ) {
  open INFILE, $fname;
  while (<INFILE>) {
    chomp;
    $last_line = $_;
  }
  close INFILE;
  print "$fname:$last_line\n";
  $last_line = '';   # in case 2nd or 3rd file is empty
}