ISR Computing -

Unix shell script to calculate date in the future and in the past

For Linux use the following commands:

$ date -d 'now + 12 days' (12 days in the future)
$ date -R --date="-14 days" (14 days in the past)

What if you have Solaris "date", then you need the below.

Let's say we need to calculate yesterday's date. This script is for Solaris only, and it is using (/abusing) TZ beyond its stated purpose. You can advance unlimited time into the future, but only 6 days into the past.

Test:

date.sh 1 past short

Content:

cat date.sh
#!/bin/ksh
if [ $# -ne 3 ]; then
 print "Usage: `basename $0` < NUMBER_OF_DAYS > < past|fut > < short|long|slong >"
 exit 1
fi
DAYS=$1
WHEN=$2
FORM=$3
ZONE=`date +%Z`
if [ "${ZONE}" = "EDT" ]; then
 HR_DIFF=4
elif [ "${ZONE}" = "EST" ]; then
 HR_DIFF=5
else
 print "${ZONE} is invalid"
 exit 1
fi
 
if [ "${WHEN}" = "past" ]; then
 SYM="+"
 HOURS=`expr ${DAYS} \* 24 + ${HR_DIFF}`
elif [ "${WHEN}" = "fut" ]; then
 SYM="-"
 HOURS=`expr ${DAYS} \* 24 - ${HR_DIFF}`
else
 print "${WHEN} is invalid"
 exit 1
fi

if [ "${FORM}" = "short" ]; then
 echo "`TZ=${ZONE}${SYM}${HOURS} date +%Y%m%d`"
elif [ "${FORM}" = "long" ]; then
 echo "`TZ=${ZONE}${SYM}${HOURS} date '+%b %d, %Y'`"
elif [ "${FORM}" = "slong" ]; then
 echo "`TZ=${ZONE}${SYM}${HOURS} date '+%b %d, %Y %H:%M'`"
else
 print "${FORM} is invalid"
exit 1
fi

exit 0