UNIX previous month and year with format YYYYMM - date

Question

I need to assign a variable with the value in the format YYYYMM e.g for today run the previous month values should be generated as
Var1 = 201607
Is there any in build method available? Could you share the steps to generate this?

Answer 1

The trick in these cases is to subtract one month from the day 15 of the current month:
$ date --date="$(date +%Y-%m-15) - 1 month"
Fri Jul 15 00:00:00 CEST 2016
Then it is just a matter of using the proper format:
$ date --date="$(date +%Y-%m-15) - 1 month" "+%Y%m"
201607
To store the value in a var, just use the common var=$(command) syntax.
From GNU Coreutils → 28.7 Relative items in date strings:
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!
Also, take care when manipulating dates around clock changes such as
daylight saving leaps. In a few cases these have added or subtracted
as much as 24 hours from the clock, so it is often wise to adopt
universal time by setting the TZ environment variable to ‘UTC0’ before
embarking on calendrical calculations.