How do i get last sunday date from a given date in unix

Question

get last sunday date as output from a given date (not current date) as input

Example input: 08-30-2017 (%m-%d-%Y)

output should be last sunday: 08-27-2017

Answer 1

Very simple way-

First calculate dayofweek from given date. It will be 1-7. For Monday it's 1 etc ...Saturday 6 and Sunday 7.

Then subtract dayofweek from given date. That's your last Sunday.

$ givenDate="08-30-2017"
$ dayofweek=$(date -j -f '%m-%d-%Y' $givenDate +'%u')
$ date -j -f '%m-%d-%Y' -v-${dayofweek}d $givenDate +%m-%d-%Y
08-27-2017