subtract days from a date in bash

Question

I want to subtract \"number of days\" from a date in bash. I am trying something like this ..

echo $dataset_date #output is 2013-08-07

echo $date_diff #outp         


        

Answer 1

To me, it makes more sense if I put the options outside (easier to group), in case I will want more of them.

date -d "$dataset_date - $date_diff days" +%Y-%m-%d

Where:

 1. -d --------------------------------- options, in this case 
                                         followed need to be date 
                                         in string format (look up on $ man date)
 2. "$dataset_date - $date_diff days" -- date arithmetic, more 
                                         have a look at article by [PETER LEUNG][1]
 3. +%Y-%m-%d -------------------------- your desired format, year-month-day