shell: date command identify last 3 previous months

shell: date command identify last 3 previous months

#!/bin/bash
set -x

echo "[$(date "+%Y-%m-%d %H:%M:%S")] started ..."

# set date
month=$(date +"%-m")
month_prev=$((month - 3))
month_end=$month
month_start=$(date -d "$(date +%Y-%m-1) -3 month" +%-m)

year=$(date +"%Y")
year_prev=$(date -d "$(date +%Y-%m-1) -1 year" +%-Y)
year_end=$year
# year_start
if [ $month -eq 1 ] || [ $month -eq 2 ] || [ $month -eq 3 ]; then
        year_start=$year_prev
else
        year_start=$year
fi