Question

In a shell script lets say i have run a command like this

for i in `ps -ax|grep "myproj"`
do
  echo $i
done

Here, the grep command would be executed as a separate process. Then how do i get its PID in the shell script ?

Answer 1

I’m going out on a limb here, and understand this looks more like a comment.

Why do you need the PID of the grep command?

In your comment you say you want to compare it in the loop against something. I would suppose that it is your issue that that the loop will (sometimes) not only include myproj but also an item about your grep command? If so, try the following:

   for i in `ps -ax | grep -v grep | grep "myproj"`
   do
      echo $i
   done

The -v switch basically inverts the pattern, so grep -v grep (or grep -v "grep", which maybe looks a bit less awkward) will include only lines that do not include the string “grep” (see man grep).
Note that this maybe overly vague for some cases, for example if the pattern you actually look for also contains the string “grep”. For example, the following might not work as you’d expect: ps -ax | grep -v grep | grep mygrepling

However, in your particular case, where you only look for “myproj” it will do.

Or you could simply use

   for i in `ps -ax | grep "my[p]roj"`
   do
      echo $i
   done

That way there is no need to know the PID of the grep command, because it simply never shows up as a loop iteration.