Shell Programming and Scripting

###############################################################################
# This Script add 30 days to current date and output next date including
# 28 or days days of February

# Author        Vaibhav Gautam
##############################################################################
#!/bin/ksh
#Start validation date is today date and validation end date is +30 days

lastday=$(cal `date '+%m'` `date '+%Y'` | grep . | fmt -1 | tail -1 )
currentdate=$(date '+%d')
currentmonth=$(date '+%m')
year=$(date '+%Y')

temp=$(($lastday - $currentdate ))

echo "Date Calculation Started"

#Next date after 30 days
#Change Value 31 for 30 days
expirydate=$((30 - $temp ))

if [ $expirydate -gt 0 ]
then
nextmonth=$(($currentmonth + 1 ))

        if [ $nextmonth -eq 2 ]
        then
                #If next month is feb then calculate last day of feb
                lastday_nextmnth=$(cal 2 `date '+%Y'` | grep . | fmt -1 | tail -1 )

                if [ $expirydate -gt $lastday_nextmnth ]
                then
                        carrydate=$(($expirydate - $lastday_nextmnth))
                        nextmonth=$(($nextmonth + 1))
                        echo "Current Date $currentdate/$currentmonth/$year\" Next Date \"$carrydate/$nextmonth/$year\""
                else
                        carrydate=$(($expirydate))
                        echo "Current Date $currentdate/$currentmonth/$year\" Next Date \"$carrydate/$currentmonth/$year\""
                fi
        else
        if [ $nextmonth -gt 12 ]
                then
                nextmonth=1
                nextyear=$(($year + 1 ))
                echo "Current Date $currentdate/$currentmonth/$year\" Next Date \"$expirydate/$nextmonth/$nextyear\""
                else
                echo "Current Date $currentdate/$currentmonth/$year\" Next Date \"$expirydate/$nextmonth/$year\""
                fi
        fi
else
expirydate=$lastday
echo "Current Date $currentdate/$currentmonth/$year\" Next Date \"$expirydate/$currentmonth/$year\""
fi

$ date
Thu Jul  9 09:48:10 EDT 2009
$ printf "%T\n" "now + 30 days"
Sat Aug  8 09:48:47 EDT 2009
$