Curl/Wget based website availability checker

website_checker.sh

#!/usr/bin/bash

#set -e
#set -x
#set -o pipefail

log_message() {
  LOGPREFIX="[$(date '+%Y-%m-%d %H:%M:%S')][$(basename ${0%})]"
  MESSAGE=$1
  echo "$LOGPREFIX $MESSAGE"
}

URL=$1

if [ "${URL}" = "" ]; then
  log_message "ERROR: URL must not be empty"
  exit 1
fi

URL_HASH=$(echo -n "${URL}" | md5sum | awk '{print $1}')

CACHE_NAMESPACE="/tmp/cwh_${URL_HASH}"
PREV_RESULT_FILE="${CACHE_NAMESPACE}_prev"
CURR_OUTPUT_FILE="${CACHE_NAMESPACE}_curr"
CURR_OUTPUT_FILE_TMP="${CACHE_NAMESPACE}_curr.tmp"
DIFF_OUTPUT_FILE="${CACHE_NAMESPACE}_diff.txt"

touch $PREV_RESULT_FILE
log_message "URL = ${URL} , URL_HASH = ${URL_HASH}, CACHE_NAMESPACE = ${CACHE_NAMESPACE}, PREV_RESULT_FILE = ${PREV_RESULT_FILE}, CURR_OUTPUT_FILE = ${CURR_OUTPUT_FILE}"

DOMAIN=$(echo "$URL" | sed -e 's|^[^/]*//||' -e 's|/.*$||')

MAX_RETRIES=10
RETRY_DELAY=5

echo "" > $CURR_OUTPUT_FILE

#for ((i=1; i<=MAX_RETRIES; i++)); do
#    host "${DOMAIN}" > $CURR_OUTPUT_FILE_TMP 2>&1
#    EXIT_CODE=$?
#    log_message "Resolving hostname, attempt ${i} , exit code = ${EXIT_CODE} , output = $(cat ${CURR_OUTPUT_FILE_TMP})"
#    if [ $EXIT_CODE -eq 0 ]; then
#        break
#    fi
#    sleep $RETRY_DELAY
#done
#cat $CURR_OUTPUT_FILE_TMP >> $CURR_OUTPUT_FILE

for ((i=1; i<=MAX_RETRIES; i++)); do
    #wget -q -O - "$URL" > $CURR_OUTPUT_FILE_TMP 2>&1
    curl --no-progress-meter "$URL" > "$CURR_OUTPUT_FILE_TMP" 2>&1
    EXIT_CODE=$?
    log_message "Fetching URL, attempt ${i} , exit code = ${EXIT_CODE} , output = $(cat ${CURR_OUTPUT_FILE_TMP})"
    if [ $EXIT_CODE -eq 0 ]; then
        break
    fi
    sleep $RETRY_DELAY
done
cat $CURR_OUTPUT_FILE_TMP >> $CURR_OUTPUT_FILE

diff "$PREV_RESULT_FILE" "$CURR_OUTPUT_FILE" > $DIFF_OUTPUT_FILE
DIFF_EXIT_CODE=$?

if [ $DIFF_EXIT_CODE -eq 0 ]; then
    log_message "Result did not change"
else
    log_message "Result CHANGED"
    SUBJECT="Curl alert for ${URL} , result changed at $(date '+%Y-%m-%d %H:%M:%S')"
    MESSAGE="Curl result changed for ${URL} , see report for details"
    log_message "Sending alerts , SUBJECT = ${SUBJECT} , MESSAGE = ${MESSAGE}"
    echo $MESSAGE | mail -s "${SUBJECT}" -A "${DIFF_OUTPUT_FILE}" __________MY_EMAIL___________
	
    mv "$CURR_OUTPUT_FILE" "$PREV_RESULT_FILE"
fi