mjhjmtu

I want to use a variable inside date command . GNU date is not supportable in my system.
I use Sunos and when I use date with -d option it is shwoing -d as bad substitution.

#!/usr/bin/ksh
RELEASE_DATE="28 OCT 2018" 
RELEASE_DATE_MINUS_2=`date -"$RELEASE_DATE: -2 $RELEASE_DATE:4:3 $RELEASE_DATE:0:4 - 2 days" '+%Y-%m-%d'`
echo "Release is $RELEASE_DATE" 
echo "release_date-2 is $RELEASE_DATE_MINUS_2

I have tried the above code snippet.
I should pass the actual release_date which i get it form another .cnf file
like 28OCT2018 with this input I should get two days before that date like 2018-10-26.

With the zsh shell:

zmodload zsh/datetime
rel_date=2018OCT28
strftime -rs d %Y%b%d.%H $rel_date.12 &&
 strftime -s two_days_before %Y-%m-%d $((d - 86400*2)) || exit

echo $two_days_before

You tagged this with shell so I will assume the variable is supposed to be in shell but FYI you cannot have spaces around the = for a shell variable.

GNU date will not accept your input date in that format but will accept it like 28 OCT 2018 so using shell parameter expansion we can rearrange the date (as long as it will always be in the same format):

date -d "$rel_date: -2 $rel_date:4:3 $rel_date:0:4"

Now in order to subtract 2 days we simply need to add:

date -d "$rel_date: -2 $rel_date:4:3 $rel_date:0:4 - 2 days" 

And to have it output in your requested format

date -d "$rel_date: -2 $rel_date:4:3 $rel_date:0:4 - 2 days" '+%Y-%m-%d'

Perl can be useful for this:

perl -MTime::Piece -slE 'say +(Time::Piece->strptime($date, "%Y%b%d") - 2 * 86_400)->ymd' -- -date="$rel_date"

You specify the format of the incoming date variable to parse it into a time object, do the date arithmetic, then output into the desired YYYYY-mm-dd format.

Documented here: https://perldoc.perl.org/Time/Piece.html

It could be useful to know which ksh88,93 are you using.

According to ksh93(1) you can find something about date:

 printf format [ arg ... ]
 %(date-format)T

--practical example

: printf "%(%d.%m,%Y)Tn" 
11.01,2019
: printf "%(%d.%m.%Y)Tn" "2 days ago"
09.01.2019

Let's hope it helps you.