Page 237 - Asterisk™: The Future of Telephony

agi_extension: 123
agi_priority: 2
After sending these variables, Asterisk sends a blank line. This is the signal that Asterisk
is done sending the variables, and it is time for the AGI script to control the dialplan.
At this point, the AGI script sends commands to Asterisk by writing to STDOUT. After
the script sends each command, Asterisk sends a response that the AGI script should
read. These actions (sending commands to Asterisk and reading the responses) can
continue for the duration of the AGI script.
You may be asking yourself what commands you can use from within your AGI script.
Good question—we’ll cover the basic commands shortly. *

Calling an AGI Script from the Dialplan

In order to work properly, your AGI script must be executable. To use an AGI script
inside your dialplan, simply call the AGI() application, with the name of the AGI script
as the argument, like this:
exten => 123,1,Answer()
exten => 123,2,AGI(agi-test.agi)
AGI scripts often reside in the AGI directory (usually located
in /var/lib/asterisk/agi-bin), but you can specify the complete path to the AGI script.

AGI(), EAGI(), DeadAGI(), and FastAGI()

In addition to the AGI() application, there are several other AGI applications suited to
different circumstances. While they won’t be covered in this chapter, they should be
quite simple to figure out once you understand the basics of AGI scripting.
The EAGI() (enhanced AGI) application acts just like AGI() but allows your AGI script
to read the inbound audio stream on file descriptor number three.
The DeadAGI() application is also just like AGI(), but it works correctly on a channel
that is dead (i.e., a channel that has been hung up). As this implies, the regular AGI()
application doesn’t work on dead channels.
The FastAGI() application allows the AGI script to be called across the network, so that
multiple Asterisk servers can call AGI scripts from a central location.

In this chapter, we’ll first cover the sample agi-test.agi script that comes with Asterisk
(which was written in Perl), then write a weather report AGI program in PHP, and finish
up by writing an AGI program in Python to play a math game.

* To get a list of available AGI commands, type show agi at the Asterisk command-line interface. You can also
refer to Appendix C for an AGI command reference.

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