And does the sub receive the file correctly? When I run the script it gives the same answer(total words) for each text file, which is incorrect.

Professor Cowdawg just drew a red "X" across your assignment.

sub countWords {
  my $fname=join("/",@_);
   
   open FIN,"< $fname" or die "$fname:$!";
   my @lines=<FIN>;
   chomp @lines;
   close FIN;
   my $count=0;
   foreach my $line(@lines){
       map { $count++ } split (/[\s\t\n]+/,$line);
   } 
   printf "There are %d words in %s\n",$count,$fname;
}
[download]

You are not counting anything in your sub at all. You actually have to read the file in order to count the words in it.