[R] Multiple match function?

[Jonck van der Kogel]

Hi all,
I have (yet another) question about a function in R. What I would like 
to do is test for the presence of a certain value in a vector, and have 
the positions that this value is at returned to me.
For example, let's say I have a vector:
x <- c(1,1,2,2,3,3,4,4)

Now I would like a function that would return positions 3 and 4 should 
I test for the value "2". Or 5 and 6 should I test for "3".

Could someone please tell me how I should do this? The "match" function 
only returns the first position that a value is found at. Of course I 
could write my own function that loops through the vector and tests for 
the presence of each value manually but it seems likely that a function 
that does this is already present in R. No need to re-invent the wheel 
:-)

Thanks very much, Jonck