Switching to VoIP

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Asterisk Dial-Plan

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installed; otherwise, it can be used to connect the call with a fax machine on an

analog channel.)

String Processing in the Dial-Plan

Since the dial-plan defines call flows, it infers programmatic logic. So, when you set

up a dial-plan, you’re really programming the PBX. For that reason, Asterisk includes

some syntactic capabilities that make your life as a PBX programmer simpler. One of

the most important of these capabilities is string processing.

In most dial-plan commands, arguments are supplied as textual expressions. They

may contain a mixture of literal values and variables. These expressions may be used

in whole or in part—through Asterisk’s extensive chopping capabilities. Consider

the following:

exten => 1,1,SetVar(wholename=DestinysEnd)

exten => 1,2,SetVar(firstword=${wholename:1:8})

In this example, ${wholename} is assigned the value DestinysEnd. Then, in the next

priority,

${firstword} is assigned the value of the first eight characters of

${wholename}. The syntax for string chopping and substringing is as follows:

${substring} = ${string:offset:length}

If the offset is less than 0, then it will be an offset from the end of the string, not the

beginning. If length isn’t supplied, the remainder of the string, from the offset on,

will be included in the