Use crontab to monitor the failure of a script

check_errors.sh

#!/bin/bash

LOG_FILE="/Users/username/output.log"
NOTIFIED_FILE="/Users/username/notified.txt"
EMAIL="username@example.com"

# Read the contents of the notified file, if it exists
notified=$(cat "$NOTIFIED_FILE" 2>/dev/null)

# If the notified file doesn't exist, assume no previous notification
if [ -z "$notified" ]; then

    # Detect errors
    new_errors=$(awk '/Execution halted/ {print $1}' "$LOG_FILE")

    # If there are new errors, send a notification
    if [ -n "$new_errors" ]; then
	# Send a notification via email
	mail -s "Cron Job Failure" $EMAIL <<EOF
    There was an error in the cron job. Check the log file: $LOG_FILE

    Log file contains:

    $(cat $LOG_FILE)

    This message will not be sent again until $NOTIFIED_FILE is cleared.
EOF

	# Update the notified file
	echo "1" > "$NOTIFIED_FILE"

    fi

fi

check_errors_ntfy.sh

#!/bin/bash

LOG_FILE="/Users/username/output.log"
NOTIFIED_FILE="/Users/username/notified.txt"
TOPIC="example_topic_changeme"

# Read the contents of the notified file, if it exists
notified=$(cat "$NOTIFIED_FILE" 2>/dev/null)

# If the notified file doesn't exist, assume no previous notification
if [ -z "$notified" ]; then

    # Detect errors
    new_errors=$(awk '/Execution halted/ {print $1}' "$LOG_FILE")

    # If there are new errors, send a notification
    if [ -n "$new_errors" ]; then
	# Send a notification via ntfy
	curl \
    	    -T $LOG_FILE \
	    -H "Title: Cron Job Failure" \
	    -H "Tags: warning" \
	    -H "Filename: $LOG_FILE" \
	    "ntfy.sh/$TOPIC"

	    # Update the notified file
	    echo "1" > "$NOTIFIED_FILE"

    fi

fi

crontab.example.txt

*/2 * * * * /usr/local/bin/Rscript -e "R.version; cat('Execution halted\n')" > /Users/username/output.log 2>&1
*/5 * * * * /Users/username/check_errors.sh