enumerate_months_in_range.sh

#!/usr/bin/env bash

DATE_RANGE=$1; # 2023-05-01,2023-11-01

if [[ -z "$1" ]]; then
    echo "must specify date range (format YYYY-MM-DD,YYYY-MM-DD) as 2nd argument"
    exit 1
fi;

IFS=",;:" read -r START_DATE END_DATE <<< "${DATE_RANGE}";

# truncate to the nearest month any dates that will be added to array
NEXT_MONTH=$(date -jf "%Y-%m-%d" "${START_DATE}" +%Y%m01);
# leave final date as-is to include start of that month if it falls before this final date
FINAL_DATE=$(date -jf "%Y-%m-%d" "${END_DATE}" +%Y%m%d);
echo "date range = [${NEXT_MONTH}, ${FINAL_DATE}]";

MONTHS=();

while [[ ${NEXT_MONTH} -lt ${FINAL_DATE} ]]; do
    MONTHS+=("${NEXT_MONTH}");
    NEXT_MONTH=$(date -v +1m -jf "%Y%m%d" "${NEXT_MONTH}" +"%Y%m01");

    echo "most recent incremented month: ${MONTHS[${#MONTHS[@]}-1]}";
done;

printf -v MONTHS_CONCAT '%s,' "${MONTHS[@]}"
echo "${MONTHS_CONCAT%,}"