logmonitor.sh

#!/bin/bash

# Send an email when a pattern is matched in a log file.
# Example usage:
#    /usr/local/bin/logmonitor.sh /var/log/nginx/error.log '[crit|error]' skyler@coefficientinc.com

PROGNAME=$0

function usage {
    echo "usage: $PROGNAME logfile pattern recipients lines"
    echo "-logfile       the log file to monitor"
    echo "-pattern       the grep pattern to match"
    echo "-recipients    comma-separated email addreses"
    echo "-lines         the number of surrounding lines to include. The default is 100."
}

# Show usage if we're missing the first three arguments
# or if the 4th is < 4 chars, which indicates that it probably isn't a valid list of recipients.
if [ $# -lt 3 ] || [ ${#3} -lt 4 ]; then
    usage
    exit 0
fi

LOGFILE=$1
PATTERN=$2
RECIPIENTS=$3
C_LINES=100

if [ ! -z "$4" ]; then
    C_LINES="$4"
fi

SUBJECT="Log Error! $LOGFILE"

tail -Fn0 "$LOGFILE" | while read line; do
    echo $line | grep --quiet "$PATTERN"
    if [ $? -eq 0 ]; then
        # Search the file backwards.
        # If there's a duplicate log entry we'll get the most recent one.
        report=$(tail -n 1000 $LOGFILE | tac | grep -F -m 1 -C "$C_LINES" "$line" | tac)
        echo "$report" | mail -s "$SUBJECT" "$RECIPIENTS"
    fi
done