#!/usr/bin/env bash
start_date="20180726"
end_date="20180830"
while [ "$start_date" -le "$end_date" ];
do
  stat_date=`date -d "$start_date" +%Y-%m-%d`
  echo $stat_date
  start_date=$(date -d "$start_date+1days" +%Y%m%d)
done1

#! /bin/bash
first=$1
second=$2
while [ "$first" != "$second" ]
do
echo $first
let first=`date -d "-1 days ago ${first}" +%Y%m%d`
done