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Alrighty. You’ve got the basics of dialplans down, and you’re hoping there’s more to come. Fear not; there is more—much more. If you don’t have the last chapter sorted out yet, please go back and give it another read. We’re building on what we’ve covered so far, and we need you to be comfortable with the material, as we’re about to get into more advanced topics.
Before we dive further into dialplans, we need to introduce you to a few tricks that will greatly add to the power you can exercise with your dialplan. These constructs add incredible intelligence to your dialplan, by enabling it to make decisions based on all sorts of different criteria. Put on your thinking cap, and let’s get started.
Expressions are combinations of variables, operators, and values
that you put together to get a result. An expression can test values,
alter strings, or perform mathematical calculations. Let’s say we have
a variable called
COUNT. In plain
English, two expressions using that variable might be "
COUNT plus 1” and "
COUNT divided by 2.” Each of these
expressions has a particular result or value, depending on the value
of the given variable.
In Asterisk, expressions always begin with a dollar sign and an opening square bracket and end with a closing square bracket, as shown below:
Thus, we ...