for example , below example is simple. DATE=$(date -v-7d ) echo $DATE
but how to calculate
2019-02-28 00:00:00 - or + 01:30:00 # date&time - or + time
or
2019-02-28 00:00:00 - or + 2019-02-20 13:30:35 # date&time - or + date&time
thanks