add script to watch changes of summary web page

update

@@ -5,7 +5,7 @@ CSV_URL="https://www8.cao.go.jp/chosei/shukujitsu/syukujitsu.csv"
 MAIL_TO="$USER"
 MAIL_FROM="info@holiday.kareha.org"
 MAIL_SUBJECT="Holiday CSV Updated"
-MAIL_BODY="Holiday CSV file has been Updated."
+MAIL_BODY="Holiday CSV file has been updated."
 
 # Constants
 EXIT_SUCCESS=0
@@ -25,10 +25,10 @@ verify_command "awk"
 verify_command "mailx"
 
 # Logging
-CURRENT_MONTH=$(date "+%Yw%U%z")
+CURRENT_MONTH=$(date "+%Y-%m%z")
 SCRIPT_NAME=$(basename $0)
 LOG_DIR="log"
-LOG_FILE="$LOG_DIR/$SCRIPT_NAME_$CURRENT_MONTH"
+LOG_FILE="$LOG_DIR/$SCRIPT_NAME-$CURRENT_MONTH"
 
 get_current_time() {
   date "+%Y-%m-%d %H:%M:%S%z"
@@ -48,7 +48,7 @@ send_mail() {
 }
 
 # Acquire the lock or exit
-LOCK_DIR="lock"
+LOCK_DIR="$SCRIPT_NAME-lock"
 if ! mkdir "$LOCK_DIR" 2>/dev/null; then
   echo "Another process is holding the lock. Exiting."
   exit $EXIT_FAILURE
@@ -65,6 +65,10 @@ CSV_FILE="holidays-jp.csv"
 # Run
 curl -sS -L -o $TMP_CSV_FILE $CSV_URL
 if ! diff -q $RAW_CSV_FILE $TMP_CSV_FILE >/dev/null 2>&1; then
+  CACHE_DIR="cache"
+  mkdir -p "$CACHE_DIR"
+  CURRENT_DATETIME=$(date "+%Y-%m-%d_%H:%M:%S%z")
+  cp $TMP_CSV_FILE "$CACHE_DIR/holidays-jp-$CURRENT_DATETIME.csv"
   mv $TMP_CSV_FILE $RAW_CSV_FILE
   nkf -w $RAW_CSV_FILE >$ALL_CSV_FILE
   current_year=$(date +'%Y')