[R] perl expression question

[markleeds at verizon.net]

I have a string such as

fileName<-"Agg.20.20.20-all-01".

All I want to do is pull the "20.20.20" and the "all" as strings.

Obviously, they aren't always those values.

The "20.20.20" can be "30.30.30" but it's always after the . which is 
next to the second g in Agg and it's always the same length. The all 
might not always be "all" but in general  it is the text between the two 
dashes.

I made an attempt using below but perl expressions and myself are an 
extremely bad match ( pun was intended ) and all I got back was the same 
string as
fileName in both cases.

  weights=sub("^Agg.(\\.*)-\\.*$", "\1",fileName)
  dashesstring=sub("^Agg.\\.*-(\\.*)-\\.*$", "\1",fileName)

I could possibly using strsplit but I'm trying to learn perl expressions 
as best I can so a solution using that approach is really appreciated. 
Thanks.