#!/usr/bin/env bash
BASE_DIR=$1

if [ ! -d "${BASE_DIR}" ] ; then
echo "$BASE_DIR is not a directory";
fi

## Find those files that are older than a month
find "$BASE_DIR" -maxdepth 1 -mtime +30 -type f -name '*.jpg' |
while IFS= read -r file; do
## Get the file's modification year
year="$(date -d "$(stat -c %y "$file")" +%Y)"
## Get the file's modification month
month="$(date -d "$(stat -c %y "$file")" +%b)"

## Create the directories if they don't exist. The -p flag
## makes 'mkdir' create the parent directories as needed so
## you don't need to create $year explicitly.
[[ ! -d "$BASE_DIR/$year/$month" ]] && mkdir -p "$BASE_DIR/$year/$month";

## Move the file
mv "$file" "$BASE_DIR/$year/$month"
done