This bash script calculates the sharpratio on yahoo finance data

sharpratio.sh

#!/bin/bash
# this script will read in a ohlc file from yahoo finance line by line
# putting every line in a list / array as an element
# and then do some basic calculations on the numbers
# we will calculate the absolute return, the avarage daily differences,
# the standard deviation of the daily differences and finally the sharp ratio

fname=$1

readin(){
	while read line
	do
	filearray+=("$line")
	done < $fname
}

readout(){
	# initialize some variables we need later for calculations in the loop
	absret=0
	dailydifsq=0
	sumofdailydifsq=0
	stdev=0
	# now let's loop through the array
	# skip index zero because we use it as base: we cannot compare it to index -1 there is no.
	for ((i=1; i < ${#filearray[*]}; i++)) 
	do
		#echo  $i
		daybefore=`(echo ${filearray[$i-1]}) | awk -F , '{print $7}'`
		today=`(echo ${filearray[$i]}) | awk -F , '{print $7}'`
		dailydif=$(echo "scale=4;(($today-$daybefore)/$daybefore)*100"|bc)
		echo "daily difference is $dailydif %"
		absret=$(echo "scale=4;$absret+$dailydif"|bc) #sum of daily dif = abs return
		echo "abs return sofar is $absret"
		dailydifsq=$(echo "scale=4;$dailydif*$dailydif"|bc) # needed for calculating the stdev
		sumofdailydifsq=$(echo "scale=4;$sumofdailydifsq+$dailydifsq"|bc) # we wanna have the sum of all squared daily difs

	done
	avdd=$(echo "scale=4;$absret/$i"|bc) #average dailydiff
	stdev=$(echo "scale=4;sqrt($sumofdailydifsq/$i)"|bc) # here we use the sum of all daily difs, devide it by the count, and then take the square root.
	sharpratio=$(echo "scale=4;($avdd/$stdev)*sqrt(252)"|bc)
	#sharpratio is the avarage daily dif devided by the stdev and then multiplied by the sqrt of 252 for dauly pricing

	echo "abs return has been $absret%"
	echo "av daily diff has been $avdd%"
	echo "stdev of daily diff has been $stdev"
	echo "the sharpratio has been $sharpratio"
}

readin
readout