Well, some examples of what you have tried and why it doesn't work would help us better understand what you need...

Here is some code to get you started:

# remember to use strict, warnings, etc

open LOG, ">$logfile" or die $!;

# You will need to update this:
# go through each .txt file in DIR
for my $file (<DIR/*.txt>) {
   # open the file
   open F, $filename or die $!;
   my ($total, $count) = @_;
   while (<F>) {
      $count ++; # the total number of samples
      $total += $_; # the running accumulator
   }
   close F;
   # remove the int if you want a decimal number.
   my $avg = int $total/$count;
   print LOG "$avg\n";
}
close LOG;
[download]