How do I implement this in shell script?

[sandeep t]

Hi,
I work on many platforms like windows, Linux, Solaris,etc.
I have an executable which can be run from any platform. Now that the process is automated, I have to find out the way to ensure that the exe is run on any one platform at one time.
lets take an example that I have a shell script at some common location, which calls this exe. and this script is run on 3 machines simultaneously.
I came with an idea that just before the start of the exe, the script will create a file "IN_PROCESS" at the common location. and once the exe is exited, the file shoudl be removed. If during running of the exe on one platform, other platform will first check the existence of the file. If file exists then it should wait till the file is non-existent.
But I'm not able to write the logic properly. can somebody help how can i implement this?

Thanks

[Freston]

That's good reasoning. And not at all difficult. You can look at your bootscripts for examples, because they often do the same check before loading services, although they don't look for the existance, but rather the executability (<=new word?) of a file. Their test is '-x' in stead of '-e' in your case. <man test> gives you a full range of options.


In BASH:

# Non-tested example code
if [ -e /$PATH/IN_PROCESS ] ; then    # If file exists, then
    echo 'Process already running'    # Say it's running and
    exit $PROCESS_EXISTS            # Exit with non-zero status (variable needs to be defined or hard coded)
else                                # Else (if file doesn't exist)
    /$PATH/$EXE                    # Start executable
fi

In this example code I assume you predefine the variables. You could also hard code them. for example
exit 1
would be valid. The same goes for $PATH and $EXE


---


Another way to do this is to search through to output of <ps aux> to see if the process is running.

[sandeep t]

I do not want to exit if that process is running. It should wait till that file is non-existent.
I have used this logic:

while test -f $PATH/IN_PROCESS
do
 echo "Process already running"
done
touch $PATH/IN_PROCESS
/$PATH/$EXE 
rm -f $PATH/IN_PROCESS

Also, can you please tell me what is the difference between '-e' and '-f'.

[Freston]

Oh! While rereading your post, I noticed you don't want the script to exit, but rather wait until the file no longer exists. That calls for a different approach.

while 
    [ -e /$PATH/IN_PROCESS ]
do
    sleep 5
done

/$PATH/$EXE

This checks every five seconds, and starts the executable after it no longer finds the file.

[Freston]

Ah! We where at it at the same time.

The difference between -e and -f isn't really important in this context. -e looks for the existence of a file. -f tests whether the file exists and is a regular file.


Both will come up 'true'

while test -f $PATH/IN_PROCESS
do
 echo "Process already running"
done
touch $PATH/IN_PROCESS
/$PATH/$EXE 
rm -f $PATH/IN_PROCESS

You will want to put the sleep command in there, or your machine will use every and all of it's raw power to fanatically test whether the file is present