open (my $fh, "<", $ARGV[0]) or die "Can't open input file!";
my @words;
  ### The above die function should also return OS_ERROR if open function failed
  ###  ... die "can't open file: $!";
while (<>) {
  ### <> will read from the STDIN not the filehandler $fh
  ### so that should be while(<$fh>){...}
    push(@words, $_);
}