6.2. Dialplan Functions

Dialplan functions allow you to add more power to your expressions—you can think of them as intelligent variables. Dialplan functions allow you to calculate string lengths, dates and times, MD5 checksums, and so on, all from within a dialplan expression.

6.2.1. Syntax

Dialplan functions have the following basic syntax:

    FUNCTION_NAME(argument)

Much like variables, you reference a function's name as above, but you reference a function's value with the addition of a dollar sign, an opening curly brace, and a closing curly brace:

    ${FUNCTION_NAME(argument)}

Functions can also encapsulate other functions, like so:

    ${FUNCTION_NAME(${FUNCTION_NAME(argument)})}
     ^             ^ ^             ^        ^^^^
     1             2 3             4        4321

As you've probably already figured out, you must be very careful about making sure you have matching parentheses and braces. In the above example, we have labeled the opening parentheses and curly braces with numbers and their corresponding closing counterparts with the same numbers.