2018-05-11 请告诉我这个脚本干了啥？

!/bin/sh

days=$1
defaultdays=4
days=${days:-$defaultdays}

days=${days:-defaultdays}

today=$(date -I|awk -F "-" '{print $1""$2""$3}')
today_pre=$(date -I|awk -F "-" '{print $1""$2}')
today_day=$(date -I|awk -F "-" '{print $3}')

until [ $days == 0 ]
do
day=$today_pre$today_day
redisconver $day
today_day=expr "$today_day" "-" "1"
days=expr "$days" "-" "1"
done

几百年没打开我的sublime text 了？