System information

There are many predefined channel variables available for use within the dialplan,
which are explained in the Asterisk wiki at https://wiki.asterisk.org/wiki/display/AST/
Channel+Variables. Channel variables are set via the Set() application:
exten => 202,1,Set(MagicNumber=42)
same => n,SayNumber(${MagicNumber})
You’re going to be seeing a lot more channel variables. Read on.
Environment variables
Environment variables are a way of accessing Unix environment variables from within
Asterisk. These are referenced using the ENV() dialplan function.
*
The syntax looks like
${ENV(var)}, where var is the Unix environment variable you wish to reference. Envi-
ronment variables aren’t commonly used in Asterisk dialplans, but they are available
should you need them.
Adding variables to our dialplan
Now that we’ve learned about variables, let’s put them to work in our dialplan. We’re
going to add three global variables that will associate a variable name to a channel name:
[globals]
LEIF=SIP/0000FFFF0001
JIM=SIP/0000FFFF0002
RUSSELL=SIP/0000FFFF0003
[LocalSets]
exten => 100,1,Dial(${LEIF})
exten => leif,1,Dial(${LEIF})
exten => 101,1,Dial(${JIM})
exten => jim,1,Dial(${JIM})
exten => 102,1,Dial(${RUSSELL})
exten => russell,1,Dial(${RUSSELL})
[TestMenu]
exten => 201,1,Answer()
same => n,Background(enter-ext-of-person)
same => n,WaitExten()
exten => 1,1,Dial(DAHDI/1,10)
same => n,Playback(vm-nobodyavail)
same => n,Hangup()
exten => 2,1,Dial(SIP/Jane,10)
same => n,Playback(vm-nobodyavail)
same => n,Hangup()
* We’ll get into dialplan functions later. Don’t worry too much about environment variables right now. They
are not important to understanding the dialplan.
124 | Chapter 6: Dialplan Basics