#!/usr/bin/awk -f
#Averages a column from a given file.  The filename
# must be the first arg, and the column the second one
# hence it can only be used in a pipeline by using - 
# to indicate stdin as the input 'file'.
#
#Note the use of 'delete ARGV[2]' to stop awk thinking 
#that we are passing in a list of files to process.
#
#Any empty lines at the start or end of the file will be counted
#as 'zero' and will affect the average.

BEGIN { i=ARGV[2] ; delete ARGV[2] ; count=0 }

{ sum += $i ; count ++ }

END { printf "%5.2f\n", (sum/count) }