Asterisk: The Definitive Guide, 4th Edition

Chapter 21. Asterisk Gateway Interface (AGI)

Caffeine. The gateway drug.

—Eddie Vedder

The Asterisk dialplan has evolved into a simple yet powerful programming interface for call handling. However, many people, especially those with a prior programming background, still prefer implementing their custom call handling in a different programming language. Using another programming language may also allow you to utilize existing code for integration with other systems. The Asterisk Gateway Interface (AGI) allows the development of first-party call control in the programming language of your choice. If you are not interested in implementing call control outside the native Asterisk dialplan, you may safely skip this chapter.

Quick Start

This section gives a quick example of using the AGI. First, add the following line to /etc/asterisk/extensions.conf:

exten => 500,1,AGI(hello-world.sh)

Next, create a hello-world.sh script in /var/lib/asterisk/agi-bin, as shown in Example 21-1.

Example 21-1. A sample AGI script, hello-world.sh

#!/bin/bash

# Consume all variables sent by Asterisk
while read VAR && [ -n ${VAR} ] ; do : ; done

# Answer the call.
echo "ANSWER"
read RESPONSE

# Say the letters of "Hello World"
echo 'SAY ALPHA "Hello World" ""'
read RESPONSE

exit 0

Now, call extension 500 with AGI debugging turned on, and listen to Allison spell out “Hello World”:

*CLI> agi set debug on
AGI Debugging Enabled

    -- Executing [500@phones:1] AGI("SIP/0004F2060EB4-00000009", 
 "hello-world.sh") in new stack ...