Asterisk Channel Variables and the Asterisk::AGI Perl Module

When calling an <acronym title="Asterisk Gateway Interface">AGI</acronym> from inside your dialplan, you can pass variables to your AGI via the AGI() application call. The AGI() application takes parameters in the following format (note the ';' is only necessary in <acronym title="Asterisk Extension Language">AEL</acronym>):

AGI(command|ARG1|ARG2|ARGn);

Asterisk LogoThe additional arguments are useful when passing in non-channel variables such as those you set in your dialplan or via Read(). But, when Asterisk executes your AGI, it automatically passes in channel variables associated with the channel executing the AGI. Table 1 below lists variables common to all channels.

The Perl Asterisk::AGI module provides the ReadParse method to read the channel variables passed along by Asterisk into a hash. The following code shows the creation of the new AGI object and the method call to fill a new hash with the available channel variables.

#!/usr/bin/env perl

use Asterisk::AGI;
use strict;
use warnings;

my $agi       = new Asterisk::AGI;
my %chan_vars = $agi->ReadParse();

It's important to note that Asterisk::AGI strips the leading 'agi_' characters from all the variables that passed in. Thus, to get the Caller*ID number you need to reference $chan_vars{'callerid'}.

Variable Description


agi_channel calling channel
agi_callerid CALLERID(num)
agi_calleridname CALLERID(name)
agi_context dialplan context from which script was called
agi_extension dialplan extension from which script was called
agi_priority dialplan priority from which script was called
agi_language CHANNEL(language)

Table 1: Common Asterisk Channel Variables

For more information on AGI programming, see Nir Simionovich's book, Asterisk Gateway Interface 1.4 and 1.6 Programming.

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