Question

I am trying to get a shell script to recognize when an app instance has come up. That way it can continue issuing commands.

I’ve been thinking it would be something like this:

#/bin/bash

startApp.sh

while [ `tail -f server.log` -ne 'regex line indicating success' ]
do

sleep 5

done

echo "App up"

But, even if this worked, it wouldn’t address some concerns:

• What if the app doesn’t come up, how long will it wait
• What if there is an error when bringing the app up
• How can I capture the log line and echo it

Am I close, or is there a better way? I imagine this is something that other admins have had to overcome.

EDIT:

I found this on super user

https://superuser.com/questions/270529/monitoring-a-file-until-a-string-is-found

tail -f logfile.log | while read LOGLINE
do
   [[ "${LOGLINE}" == *"Server Started"* ]] && pkill -P $$ tail
done

My only problem with this is that it might never exit. Is there a way to add in a maximum time?

Answer 1

Ok the first answer was close, but didn’t account for everything I thought could happen.

I adapted the code from this link:

Ending tail -f started in a shell script

Here’s what I came up with:

#!/bin/bash

instanceDir="/usr/username/server.name"
serverLogFile="$instanceDir/server/app/log/server.log"

function stopServer() {

    touch ${serverLogFile}

    # 3 minute timeout.
    sleep 180 &
    local timerPid=$!

    tail -n0 -F --pid=${timerPid} ${serverLogFile} | while read line 
    do
        if echo ${line} | grep -q  "Shutdown complete"; then
          echo 'Server Stopped'
          # stop the timer..
          kill ${timerPid} > /dev/null 2>&1
        fi
    done &

    echo "Stoping Server."
    $instanceDir/bin/stopserver.sh > /dev/null 2>&1

    # wait for the timer to expire (or be killed)
    wait %sleep


}

function startServer() {

    touch ${serverLogFile}

    # 3 minute timeout.
    sleep 180 &
    local timerPid=$!

    tail -n0 -F --pid=${timerPid} ${serverLogFile} | while read line 
    do
        if echo ${line} | grep -q  "server start complete"; then
          echo 'Server Started'
          # stop the timer..
          kill ${timerPid} > /dev/null 2>&1
        fi
    done &

    echo "Starting Server."
    $instanceDir/bin/startserver.sh > /dev/null 2>&1 &

    # wait for the timer to expire (or be killed)
    wait %sleep

}

stopServer
startServer