datemath

Purpose

Perform arithmetic on a date or two dates:

• Calculate the difference between two dates
• Add or subtract a timedelta from a date

Syntax

Syntax:
        datemath date1 - date2
        datemath date1 +/- timedelta

Where:
  date1 and date2 can be expressed as:
     %Y/%m/%d		ex: 2018/04/03
     %Y/%m/%dT%H:%M	ex: 2018/04/03T12:00
     %Y/%m/%dT%H:%M:%S	ex: 2018/04/03T12:00:00
     %H:%M:%S		ex: 12:00:00
     %H:%M		ex: 12:00
  date1 can also be expressed as (but date2 cannot):
     "now"		ex: now
  timedelta can be expressed as:
     [INTd][INTh][INTm][INTs] ex: 1d12h

Example

$ date
Tue Apr  3 16:51:50 EDT 2018
$ datemath now - $(date +%Y/%m/%d)
16:51:55.474269
$ datemath now + 1d
2018-04-04 16:52:07.780467
$ datemath now - 1d
2018-04-02 16:52:10.239369
$

Notes

• When doing math between two dates, you need not worry about which date is earlier than the other. The script tells you the amount of time between the dates.
• When you specify just a date without a time, midnight is assumed.