Page 177 - Asterisk™: The Future of Telephony

exten => 123,1,Set(TEST=example)
exten => 123,n,SayNumber(${LEN(${TEST})})
The above example would evaluate the string example as having seven characters, assign
the number of characters to the variable length, and then speak the number to the user
with the SayNumber() application.
Let’s look at another simple example. If we wanted to set one of the various channel
timeouts, we could use the TIMEOUT() function. The TIMEOUT() function accepts one of
three arguments: absolute, digit, and response. To set the digit timeout with the
TIMEOUT() function, we could use the Set() application, like so:
exten => s,1,Set(TIMEOUT(digit)=30)
Notice the lack of ${ } surrounding the function. Just as if we were assigning a value
to a variable, we assign a value to a function without the use of the ${ } encapsulation.

A complete list of available functions can be found by typing core show functions at
the Asterisk command-line interface. You can also look them up in Appendix F.

Conditional Branching

Now that you’ve learned a bit about expressions and functions, it’s time to put them
to use. By using expressions and functions, you can add even more advanced logic to
your dialplan. To allow your dialplan to make decisions, you’ll use
conditional branching. Let’s take a closer look.

The GotoIf() Application
The key to conditional branching is the GotoIf() application. GotoIf() evaluates an
expression and sends the caller to a specific destination based on whether the expres-
sion evaluates to true or false.

GotoIf() uses a special syntax, often called the conditional syntax:
GotoIf(expression?destination1:destination2)
If the expression evaluates to true, the caller is sent to destination1. If the expression
evaluates to false, the caller is sent to the second destination. So, what is true and what
is false? An empty string and the number 0 evaluate as false. Anything else evaluates as
true.
The destinations can each be one of the following:

• A priority label within the same extension, such as weasels
• An extension and a priority label within the same context, such as 123,weasels
• A context, extension, and priority label, such as incoming,123,weasels

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