Page 178 - Asterisk™: The Future of Telephony

Either of the destinations may be omitted, but not both. If the omitted destination is
to be followed, Asterisk simply goes on to the next priority in the current extension.
Let’s use GotoIf() in an example:

exten => 345,1,Set(TEST=1)
exten => 345,n,GotoIf($[${TEST} = 1]?weasels:iguanas)
exten => 345,n(weasels),Playback(weasels-eaten-phonesys)
exten => 345,n,Hangup()
exten => 345,n(iguanas),Playback(office-iguanas)
exten => 345,n,Hangup()

You will notice that we have used the Hangup() application following
each Playback() application. This is done so that when we jump to the
weasels label, the call stops before execution gets to the office-
iguanas sound file. It is becoming increasingly common to see exten-
sions broken up in to multiple components (protected from each other
by the Hangup() command), each one acting as steps executed following
a GotoIf().

Providing Only a False Conditional Path

If we wanted to, we could have crafted the preceding example like this:
exten => 345,1,Set(TEST=1)
exten => 345,n,GotoIf($[${TEST} = 1]?:iguanas) ; we don't have the weasels label anymore,
; but this will still work
exten => 345,n,Playback(weasels-eaten-phonesys)
exten => 345,n,Hangup()
exten => 345,n(iguanas),Playback(office-iguanas)
exten => 345,n,Hangup()
There is nothing between the ? and the :, so if the statement evaluates to true, execution
of the dialplan will continue at the next step. Since that is what we want, a label is not
needed.
We don’t really recommend doing this, because this is hard to read, but you will see
dialplans like this, so it’s good to be aware that this syntax is totally correct.

Typically when you have this type of layout where you end up wanting to limit Asterisk
from falling through to the next priority after you’ve performed that jump, it’s probably
better to jump to separate extensions instead of priority labels. If anything, it makes it
a bit more clear when reading the dialplan. We could rewrite the previous bit of dialplan
like this:

exten => 345,1,Set(TEST=1)
exten => 345,n,GotoIf($[${TEST} = 1]?weasels,1:iguanas,1); now we're going to
; extension,priority
exten => weasels,1,Playback(weasels-eaten-phonesys); this is NOT a label.
; It is a different extension
exten => weasels,n,Hangup()

150 | Chapter 6: More Dialplan Concepts