start="22 April 2017"
end=$(date +%s -d "19 December 2017")
i=0
while (($(date +%s -d "$start + $i days") < end))
do
date +%F -d "$start + $i days"
((i+=11))
done
O GNU date
permite expressões como <date> + <n> days
. +%s
é o timestamp do Unix e +F
da data em YYYY-MM-DD
.
Saída:
2017-04-22
2017-05-03
2017-05-14
2017-05-25
2017-06-05
2017-06-16
2017-06-27
2017-07-08
2017-07-19
2017-07-30
2017-08-10
2017-08-21
2017-09-01
2017-09-12
2017-09-23
2017-10-04
2017-10-15
2017-10-26
2017-11-06
2017-11-17
2017-11-28
2017-12-09