UNIX for Dummies Questions & Answers

Hi Everybody

I have small requirement that needs to be implemented in shell script.
Currently i have shell script which invokes a java process say "Process A" which runs in background.

If some one tries to invoke again the same shell script , then there should be some mechanism inside the shell script to check whether process "Process A"(Background process) is running already or not.If it is already running ,it shud not spawn new process "Process A" again.

On a simple way i can rephrase it as "At any point of time, there should be only one process(background) running which is been invoked by Shell script".If the same shell script is again invoked ,it shud not start the process till it is shutdown.

Another info i need is

Basically i have Process ID of background process which is running currently.
I want to check whether the process that belongs to the process id is alive or not .....

Reply wud be very much appreciated

Am sure there had been so many threads regarding the same
with solutions like, having control file or pid file

or checking with ps -ef and grep in the shell script itself.

You would find your answer with search.

Among the few ways of accomplishing this, this is one way.

Code:

count=$(ps x | grep '[j]ava yourapp' | wc -l)
if [[ $count == 0 ]; then
  java yourapp
fi;

Combine grep and wc -l with " -c " option

Code:

ps x | grep '[j]ava yourapp'||java yourapp

Code:

$ sleep 5 &
[1] 24814
$ ps -p $! || echo "not running"
   PID TTY      TIME CMD
 24814 pts/1    0:00 sleep
$ 
[1]+  Done                    sleep 5
$ ps -p $! || echo "not running"
   PID TTY      TIME CMD
not running

If your ps doesn't support the p option, use "...|grep <pid>"