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exten => _0X.,1,noop() ; national dialing prefix
; Dutch Caribbean (Saba)
exten => _00X.,1,noop() ; international
exten => _416XXXX,1,noop() ; local (on-island)
exten => _0[37]XXXXXX,1,noop() ; call to country code 599 off-island (not Curacao)
exten => _09XXXXXXX,1,Noop() ; call to country code 599 off-island (Curacao)
You will need to understand the dialing plan of your region in order to produce a
useful pattern match.
Using the ${EXTEN} channel variable
So what happens if you want to use pattern matching but need to know which digits
were actually dialed? Enter the ${EXTEN} channel variable. Whenever you dial an
extension, Asterisk sets the ${EXTEN} channel variable to the digits that were received.
We used the application SayDigits() to demonstrate this.
19 If you grew up in North America, you may believe that the 1 you dial before a long-distance call is “the long-
distance code.” This is not completely correct. The number 1 is also the international country code for NANP.
Keep this in mind if you send your phone number to someone in another country. The recipient may not
know your country code, and thus be unable to call you with just your area code and phone number. Your full
phone number with country code is +1 NPA NXX XXXX (where NPA is your area code)—for example,
+1 416 555 1212. This is also known as E.164 format (Wikipedia can tell you all about E.164).
104
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Chapter 6: Dialplan Basics
exten => _4XX,1,Noop(User Dialed ${EXTEN})
same => n,Answer()
same => n,SayDigits(${EXTEN})
same => n,Hangup()
exten => _555XXXX,1,Answer()
same => n,SayDigits(${EXTEN})
In these examples, the SayDigits() application read back to you the extension you
dialed.
Often, it’s useful to manipulate the ${EXTEN} by stripping a certain number of digits
off the front of the extension. This is accomplished by using the syntax ${EXTEN:x},
where x is where you want the returned string to start, from left to right. For example,
if the value of ${EXTEN} is 95551212, ${EXTEN:1} equals 5551212. Let’s try another
example:
exten => _XXX,1,Answer()
same => n,SayDigits(${EXTEN:1})
In this example, the SayDigits() application would start at the second digit, and thus
read back only the last two digits of the dialed extension.
More Advanced Digit Manipulation
The ${EXTEN} variable properly has the syntax ${EXTEN:x:y}, where x is the starting
position and y is the number of digits to return. Given the following dial string:
94169671111
we can extract the following digit strings using the ${EXTEN:x:y} construct:
• ${EXTEN:1:3} would contain 416
• ${EXTEN:4:7} would contain 9671111
• ${EXTEN:-4:4} would start four digits from the end and return four digits, giv‐
ing us 1111
• ${EXTEN:2:-4} would start two digits in and exclude the last four digits, giving
us 16967
• ${EXTEN:-6:-4} would start six digits from the end and exclude the last four dig‐
its, giving us 67
• ${EXTEN:1} would give us everything after the first digit, or 4169671111 (if the
number of digits to return is left blank, it will return the entire remaining string)
This is a very powerful construct, but most of these variations are not very common
in normal use. For the most part, you will be using ${EXTEN} (or perhaps ${EXTEN:1}
if you need to strip off an external access code, such as a prepended 9).
Building an Interactive Dialplan
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105
Includes
Asterisk has an important feature that allows extensions from one context to be avail‐
able from within another context. This is accomplished through use of the include
directive, which allows us to control access to different sections of the dialplan.
The include statement takes the following form, where context is the name of the
remote context we want to include in the current context:
include => context
Including one context within another context allows extensions within the included