When Asterisk encounters an expression in a dialplan, it replaces the entire expression

with the resulting value. It is important to note that this takes place after variable sub-

stitution. To demonstrate, let’s look at the following code

*

:

exten => 321,1,Set(COUNT=3)

same => n,Set(NEWCOUNT=$[${COUNT} + 1])

same => n,SayNumber(${NEWCOUNT})

In the first priority, we assign the value of 3 to the variable named COUNT.

In the second priority, only one application—Set()—is involved, but three things ac-

tually happen:

1. Asterisk substitutes ${COUNT} with the number 3 in the expression. The expression

effectively becomes this:

exten => 321,n,Set(NEWCOUNT=$[3 + 1])

2. Asterisk evaluates the expression, adding 1 to 3, and replaces it with its computed

value of 4:

exten => 321,n,Set(NEWCOUNT=4)

3. The Set() application assigns the value 4 to the NEWCOUNT variable

The third priority simply invokes the SayNumber() application, which speaks the current

value of the variable ${NEWCOUNT} (set to the value 4 in priority two).

Try it out in your own dialplan.

Operators

When you create an Asterisk dialplan, you’re really writing code in a specialized script-

ing language. This means that the Asterisk dialplan—like any programming language—

recognizes symbols called operators that allow you to manipulate variables. Let’s look

at the types of operators that are available in Asterisk:

Boolean operators

These operators evaluate the “truth” of a statement. In computing terms, that es-

sentially refers to whether the statement is something or nothing (nonzero or zero,

true or false, on or off, and so on). The Boolean operators are:

expr1 | expr2

This operator (called the “or” operator, or “pipe”) returns the evaluation of

expr1 if it is true (neither an empty string nor zero). Otherwise, it returns the

evaluation of expr2.

* Remember that when you reference

a variable you can call it by its name, but when you refer to a variable’s

value, you have to use the dollar sign and brackets around the variable name.

196 | Chapter 10: Deeper into the Dialplan

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SilverStone SST-ST30NF-V4.1 manuels

Manuels d'utilisation et guides de l'utilisateur pour Unités d'alimentation électrique SilverStone SST-ST30NF-V4.1.
Nous fournissons des manuels en pdf 1 SilverStone SST-ST30NF-V4.1 à télécharger gratuitement par type de document : Manuel de l'utilisateur

Silverstone SST-ST30NF-V4.1 Manuel de l'utilisateur (16 pages)

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