Regular Expression Question

[Len Morgan]

I need to find the last matching character offset of a string withing 
another string.  The offset function only gives me the first one.  Is 
there a function I'm missing (like "offset from end of string") or a one 
or two liner I can use?

Example:

approved_by_code - I'm looking for the offset to the second "_" 
character so the result should be 12 in this example.  It is also 
possible that there will only be one "_" character in which case, that 
is the offset I want.

Thanks in advance!

Len Morgan