System information

This would have assigned the variable TEST to the string “2+1”, instead of the value 3.
In order to remedy that, we would put spaces around the operator, like so:
exten => 234,1,Set(TEST=$[2 + 1])
This is no longer necessary in current versions of Asterisk, as the expression parser has
been made more forgiving in these types of scenarios. However, for readability’s sake,
we still recommend including the spaces around your operators.
To concatenate text onto the beginning or end of a variable, simply place them together,
like this:
exten => 234,1,Set(NEWTEST=blah${TEST})
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.
Syntax
Dialplan functions have the following basic syntax:
FUNCTION_NAME(argument)
You reference a function’s name the same way as a variable’s name, 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 preceding example, we have labeled
the opening parentheses and curly braces with numbers and their corresponding clos-
ing counterparts with the same numbers.
Examples of Dialplan Functions
Functions are often used in conjunction with the Set() application to either get or set
the value of a variable. As a simple example, let’s look at the LEN() function. This
function calculates the string length of its argument. Let’s calculate the string length of
a variable and read back the length to the caller:
198 | Chapter 10: Deeper into the Dialplan