How to measure rate of new lines in file (log file)

FILE=/var/log/syslog
DELAY=10
BEFORE=$(wc -l ${FILE}|cut -f1 -d' ')
sleep ${DELAY}
AFTER=$(wc -l ${FILE}|cut -f1 -d' ')
echo $(($AFTER - $BEFORE))

Gives you a count of number of lines added in 10s.

cat /var/log/myfile | while (( ( (index++) % 5 ) == 0 )) { sms/chat-session/whatever }

update: actual general working code:

dmesg | while true; do  <br> 
    if  [  $((  $(( index++ )) % 5 )) -eq 0 ]; then
        nc  -p srcport --send-only hostname port    or arduino ...:P
        sms/write/chat-session/whatever; 
    fi  
done

snmp might be a more useful idea under certain circumstances.