open FH, '<', 'file.txt' or die ("Can't read file: $!");

my ($lines, $total_length);

while (<FH>) {
   s/\s+$//s; # trims all traling whitespace, including \n
   ++$lines;
   $total_length += length($_);
}

#loop ends automatically when you reach EOF
printf "File had %d lines, with an average length of %d chars\n",
   $lines, ($total_length / $lines);