Average file size within a directory. http://vivekjain10.blogspot.com/2008/02/average-file-size-within-directory.html

average_filesize.sh

# To calculate the average file size within a directory:
ls -l | gawk '{sum += $5; n++;} END {print sum/n;}'

# If you'd like to know the average size of some particular kind of file:
ls -l *.jpg | gawk '{sum += $5; n++;} END {print sum/n;}'