Page 165 - Asterisk™: The Future of Telephony

[globals]
JOHN=Zap/1
JANE=SIP/Jane

[incoming]
exten => 123,1,Answer()
exten => 123,n,Background(enter-ext-of-person)
exten => 123,n,WaitExten()

exten => 1,1,Dial(${JOHN},10)
exten => 1,n,Playback(vm-nobodyavail)
exten => 1,n,Hangup()
exten => 2,1,Dial(${JANE},10)
exten => 2,n,Playback(vm-nobodyavail)
exten => 2,n,Hangup()
exten => i,1,Playback(pbx-invalid)
exten => i,n,Goto(incoming,123,1)

exten => t,1,Playback(vm-goodbye)
exten => t,n,Hangup()
[employees]

exten => 101,1,Dial(${JOHN})
exten => john,1,Dial(${JOHN})
exten => 102,1,Dial(${JANE})
exten => jane,1,Dial(${JANE})
Pattern Matching

If we want to be able to allow people to dial through Asterisk and have Asterisk connect
the caller to an outside resource, we need a way to match on any possible phone number
that the caller might dial. Can you imagine how tedious it would be to manually write
a dialplan with an extension for every possible number you could dial? Luckily, Asterisk
has just the thing for situations like this: pattern matching. Pattern matching allows you
to create one extension in your dialplan that matches many different numbers.

Pattern-matching syntax
When using pattern matching, certain letters and symbols represent what we are trying
to match. Patterns always start with an underscore (_). This tells Asterisk that we’re
matching on a pattern, and not on an explicit extension name. (This means, of course,
that you should never start your extension names with an underscore.)

If you forget the underscore on the front of your pattern, Asterisk will
think it’s just a named extension and won’t do any pattern matching.
This is one of the most common mistakes people make when starting
to learn Asterisk.

Building an Interactive Dialplan | 137