Switching to VoIP

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Chapter 17: Asterisk Reference

automatically remove extensions when customers’ bills are overdue in an external

billing system.

Consider the following line of Perl:

system("asterisk –r –x add extension $newExt,$newPri,$appl,$args into $context");

This Perl command launches Asterisk in client mode and runs the add extension CLI

command with an entirely dynamic extension definition—one that another part of

the Perl script establishes according to the programmer’s design.

In order to use the CLI wrapper from a CGI script, the web server run-

ning the script must have permission to execute Asterisk. Usually, this

means putting Asterisk and your web server in the same user group.

This could pose a potential security risk, so use this trick with care.

The Asterisk Gateway Interface

One of the most compelling ingredients in the Asterisk recipe, AGI gives developers

the ability to create custom interfaces between the dial-plan and outside systems.

The AGI is to Asterisk what CGI is to a web server. In a nutshell, it allows you to use

your favorite programming language—Perl, Python, Pascal, RealBASIC, whatever—

to affect or control interaction with a telephone user who’s attached to the PBX.

Here a few examples of things you can do with the AGI:

• Show the caller ID of an incoming phone call ...