Monitor a file and send mail

Shell Programming and Scripting
1

I want to monitor the maillog file in real time and send a mail when a certain grep condition is met. Every time the grep condition is met a mail will be sent. I wish to ignore all grep conditions 30 mins after each mail and thereafter continue monitoring.

For example:

  1. Condition is met, mail is sent
  2. 30 mins no mail even if condition is met.
  3. After 30 mins again condition is met and a mail is triggered.
  4. Again for next 30 mins no mail even if condition is met.

and so on.

I am doing the following:

tail -F -n0 /var/log/maillog | \
 grep -v --line-buffered 'status=sent' | \
 grep --line-buffered -v 'relay=local' | \
 grep --line-buffered 'relay=' | \
 while read line
 do
    echo "$line" | \
    mail -s Test mail@group.com
 done

Now i am not sure how to prevent mail sending 30 mins after the event is triggered.

2

How about we remember where we are upto in the maillog and only print new stuff.
That way we can sleep for 30mins and the resume checking:

UPTO=0
MAILFILE=/var/log/maillog
while [ -f "$MAILFILE" ]
do
    FSZ=$(wc -l < "$MAILFILE")

    if [ $FSZ -lt $UPTO ]
    then
        # File has shrunk!
        # most likely been truncated - start from beginning again.
        UPTO=0
    fi

    found=$( awk -v START=$UPTO -v FINISH=$FSZ '
       NR <= START || NR > FINISH { next }
       /status=sent/ || /relay=local/ { next }
       /relay=/ { print }' "$MAILFILE" )

    if [ -z "$found" ]
    then
       # Wait for a minute for maillog to grow a bit
       sleep 60
    else
       echo "$found" | mail -s Test mail@group.com

       # No more emails for 30mins
       sleep 1800

       # If you don't want to be notified about any other
       # occurances within this 30min period uncomment below
       # FSZ=$(wc -l /var/log/"$MAILFILE")
    fi
    UPTO=$FSZ
done