#!/bin/sh

col="none"

if [ $# -ge 1 ]; then
  if [ a"$1" = a-c ]; then
    if [ $# -eq 1 ]; then
      echo 'usage: calcavg [ -c n ] [ files ]' >&2
      exit 1
    fi
    if [ "$2" -le 0 ]; then
      echo 'usage: calcavg [ -c n ] [ files ]' >&2
      exit 1
    fi
    col=$2
    shift ; shift
  fi
fi

if [ $# -eq 0 ]; then
  fn='-'
else
  fn=$*
fi

if [ $col = none ]; then
  s='for (i = 1; i <= NF ; i++) {'
else
  s="i = $col ; if (NF >= $col) {"
fi

cat $fn | awk 'BEGIN { n = 0; t = 0 }
                     { '"$s"'
                       n++ ; t += $i }}
               END   { if (n == 0) print "inf" ; else print t/n }'