substring extraction

Hi,

I need in the SELECT query extract substring 'cccc' from string 
'aaa.bbbbb.cccc.dd.eee' (extract third field from string if 
delimiter is '.').

It is easy if I know where is begin/end of 'cccc' and I can 
use the substring() function:

select substring('aaa.bbbbb.cccc.dd.eee' from 11 for 4);
substr
------
cccc

But how extract it if I don't know where is position of the second 
and third '.'? 

Yes, I know the function position() or textpos(), but this return first 
a position of the substring...

For this exist nice UN*X command "cut -f3 -d." , but how make it in 
SQL?

I ask about it, because I write for me this as new function in C, but 
I'm not sure if not exist other (better) way for it.
                    Karel


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Karel Zak <zakkr@zf.jcu.cz>                      http://home.zf.jcu.cz/~zakkr/

Docs:         http://docs.linux.cz                          (big docs archive)    
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