Shell Programming and Scripting

$ cat nextFriday.sh
getNextFridayDate()
{
	currentDayName=`date +"%A"`
	currentDate=`date +"%Y%m%d"`
	countDays=1
	while [ "${currentDayName}" != "Friday" ]
	do
		currentDayName=`date -d "${countDays} day" +"%A"`
		currentDate=`date -d "${countDays} day" +"%Y%m%d"`
		countDays=`expr ${countDays} + 1`
	done
	echo "${currentDate}"
}

nextFriDate=`getNextFridayDate`
echo "Next Friday is: [${nextFriDate}]"

$ ./nextFriday.sh
Next Friday is: [20111209]

tempFile="./fridayDate.tmp"
##########################################################
checkRetCode ()
{
	lastRetCode=$?
	if [ ${lastRetCode} -ne 0 ]
	then
		echo "Last command's return code is invalid: [${lastRetCode}]. Exitting 1."
		exit 1
	fi
}
##########################################################
setFridayInfo ()
{
	currentDayName=`date +"%A"`
	if [ "${currentDayName}" == "Friday" ]
	then
		lastFridayDate=`date +"%Y%m%d"`
		echo "Today is Friday! Writing to temp file: [${tempFile}][${tempFile}]"
		echo "${lastFridayDate}" > "${tempFile}"
		checkRetCode
	fi

	if [ -f "${tempFile}" ]
	then
		lastFridayDate=`egrep '[0-9]+' "${tempFile}"`
		lastFridayDate="${lastFridayDate:-NULL}"
		if [ ${#lastFridayDate} -ne 8 ]
		then
			echo "Temp file has an invalid date: [${#lastFridayDate}][${lastFridayDate}]. Exitting 1."
			exit 1
		fi
	else
		echo "Temp file does not exist: [${tempFile}] and weekday name is different from Friday. Exitting 1."
		exit 1
	fi
	return 0
}

##########################################################
setFridayInfo

echo "${lastFridayDate}"