grep'ping the ps output....

[Eric Schuele]

Alex Zbyslaw wrote:
> Eric Schuele wrote:
> 
>> Hello,
>>
>> 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
> 

Thanks guys.  Yes... both solutions do fix the problem.

Hmm... guess I should've looked before I lept.  I assumed the processes 
were run in order by the shell... however it appears all are started 
simultaneously as a group.

> 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.
> 
> --Alex
> 
> 
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-- 
Regards,
Eric