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 #output is 2   

p_dataset_date=`$dataset_date --date="-$date_diff days" +%Y-%m-%d` # Getting Error

Answer 1

You are specifying the date incorrectly. Instead, say:

date --date="${dataset_date} -${date_diff} day" +%Y-%m-%d

If you need to store it in a variable, use $(...):

p_dataset_date=$(date --date="${dataset_date} -${date_diff} day" +%Y-%m-%d)

Answer 2

one liner for mac os x:

yesterday=$(date -d "$date -1 days" +"%Y%m%d")

Answer 3

If you're not on linux, maybe mac or somewhere else, this wont work. you could check with this:

yesterday=$(date  -v-1d    +"%Y-%m-%d")

to get more details, you could also see

man date