[Asterisk-Users] Extracting info from the $EXTEN variable

[Álvaro Palma]

Is there a way to access only certain positions in the $EXTEN variable?
I'd like to filter my international calls based on the destination country:

My dialplan looks like this (1XX0. is the international calling 
convention for Chile)

exten => _1XX0.,1,Dial(SIP/${EXTEN:4}@external_provider)

But, I'd like to, depending on the destination country (digits 5 and 
eventually 6 of EXTEN), route my calls for another provider, something like:

exten => _1XX0.,1,GotoIf(${EXTEN[5-6]} == certain_pattern)?2,3)
exten => _1XX0.,2,Dial(SIP/${EXTEN:4}@external_provider1)
exten => _1XX0.,3,Dial(SIP/${EXTEN:4}@external_provider2)

How can I do that? I was looking the documentation, but it only speaks 
of stripping digits from the extension, not to selecting a range.

Thanks a lot for your help.

-- 
Atly.
Álvaro Palma