How does this simple awk script work?

ziggy25 · 12-11-2009, 05:59 AM

This script is supposed to find out if tomcat is running or not.

Code:

#!/bin/sh
if netstat -a | grep `grep ${1}:  /tomcat/bases | awk -F: '{print $3}'` > /dev/null
then
        echo Tomcat for $1 running
else
        echo Tomcat for $1 NOT running
fi

the /tomcat/bases is a file that contains a list of all the tomcat instances running and which port number it is running

Code:

user1:yes:8080
user2:no:8081
user3:yes:8082

I know it uses netstat to check if any of the port numbers in the "bases" file is listening but i dont quite understand how this is achieved by that command shown above.

Thanks

druuna · 12-11-2009, 07:14 AM

Hi,

netstat -a | grep `grep ${1}: /tomcat/bases | awk -F: '{print $3}'` > /dev/null

First the blue part is executed (all between both backticks), which gives back a specific port (field number 3 in /tomcat/bases) associated with the user (which is given at the command line, represented by $1). The awk command sets a different field separator (default is a space, -F: makes it a : ).

You end up with a command like this (when user1 is used at the command line):

netstat -a | grep 8080 > /dev/null

Depending on the output the process is either alive or not.

Hope this clears things up a bit.