Issue
I am using below to get previous, current and the next month under Ubuntu
11.04:
LAST_MONTH=`date +'%m' -d 'last month'`
NEXT_MONTH=`date +'%m' -d 'next month'`
THIS_MONTH=`date +'%m' -d 'now'`
It works well until today, the last day of October, 2012 (2012-10-31)
I get below result as of now:
$ date
Wed Oct 31 15:35:26 PDT 2012
$ date +'%m' -d 'last month'
10
$ date +'%m' -d 'now'
10
$ $ date +'%m' -d 'next month'
12
I suppose the outputs should be 9
,10
,11
respectively.
Don't understand why date
outputs behave like this. What should be a good way to get consistant previous
, current
and next
month instead?
Solution
The problem is that date
takes your request quite literally and tries to use a date of 31st September (being 31st October minus one month) and then because that doesn't exist it moves to the next day which does. The date
documentation (from info date
) has the following advice:
The fuzz in units can cause problems with relative items. For example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because 2003-06-31 is an invalid date. To determine the previous month more reliably, you can ask for the month before the 15th of the current month. For example:
$ date -R Thu, 31 Jul 2003 13:02:39 -0700 $ date --date='-1 month' +'Last month was %B?' Last month was July? $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' Last month was June!
Answered By - TomH Answer Checked By - Mildred Charles (WPSolving Admin)