SHELL

datetime calculation in shell

date --date "07/01/2021 +1 hours" +'%d/%m/%Y %H:%M:%S'

datetime calculation in shell

$ date --date 'March 1, 2015 +7 days'
Sun Mar  8 00:00:00 MST 2015
$ date --date 'March 1, 2015 -1 year'
Sat Mar  1 00:00:00 MST 2014
$ date --date 'March 1, 2015 +12 days +12 hours +15 minutes'
Fri Mar 13 12:15:00 MST 2015

datetime calculation in shell

$ date --date 'last Monday'
Mon Sep 10 00:00:00 MST 2018
$ date --date 'next Monday'
Mon Sep 17 00:00:00 MST 2018