How to avoid executing a command if a process doesn't exist

Question

In a korn shell script, I am running expdp. I have made the script to where it can be reusable so if a later process fails, I can run it again without running the already completed steps. I am running two processes in the background and waiting for both to complete before moving ahead in the script. For example, I am using the below logic to wait. After the expdp process completes, I am using a log function to write a completed message.

while   ps | grep "expdp" | grep -v grep
do
    echo expdp is still in the ps output. Must still be running.
    sleep 5
done

WriteLog "Completed exporting client schemas"

If the process does not exists (i.e. reusing the script after fixing any errors which occurred after expdp), how do I set it up to where the writelog occurs only when the expdp process exists. If no process is found from ps then it should not write log again.

Answer 1

I think you're seaching in a wrong way. I'd write such a script like this:

if [ "z$STEP5" != "zOK" ] ; then
    expdp -your_options > $logfile &
    while ps ax | grep [e]xpdp ; do
        echo "expdp still in progress..."
        sleep 5
    done
    wait # in order to be sure there is no more background processes...
    tail -n1 $logfile | grep "successfully without warnings" >/dev/null 2>&1
    if [ $? -ne 0 ] ; then 
        echo "Some errors occured while export"
    else
        echo "Export done sucessfully"
    fi
fi