grep'ping the ps output....
xfb52 at dial.pipex.com
Mon Dec 12 08:16:58 PST 2005
Eric Schuele wrote:
> I am sure this is quite trivial, but...
> I have need to determine if an app (firefox, or anything really) is
> already running before I perform some action. So I grep the ps
> output. However sometimes (many times) that which I'm searching for
> is present in the output because I am presently grep'ing for it. But
> it is not always there. It seems to be a bit inconsistent. (See below).
> I was wondering if someone could explain why it is sometimes there and
> not other times. And how I should correctly go about detecting if the
> process is running before I perform my action.
ps | egrep firefox | egrep -v egrep
I can't explain exactly why. It's clearly a timing thing. I guess if
the ps runs quickly enough then perhaps the grep hasn't actually been
started by the shell. Or if ps iterates over something, then maybe the
grep appears in a part of the list that has already been looked at by ps.
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