Tuesday, August 5, 2008

Asterisk variables

Using Variables in Asterisk Dialplans

Asterisk can make use of global and channel-specific variables for arguments to commands. Variables are referenced in the dialplan (extensions.conf) using the syntax


where foo is the name of the variable, offset is an optional field indicating which characters should be excluded, and length is an optional field indicating the number of characters from the offset to be returned (see "Substrings" below for details and examples). A variable name may be any alphanumeric string beginning with a letter. User-defined variable names are not case sensitive — ${FOO} and ${Foo} refer to the same variable — but Asterisk-defined variables are case-sensitive — ${EXTEN} works, but ${exten} doesn't.

There are three types of variables: global variables, channel variables, and environment variables.
  • Global variables can be set either in the [globals] category of extensions.conf or by using the SetGlobalVar command. Once defined, they can be referenced by any channel at any time.
  • Channel variables are set using the Set command (previously "setvar"). Each channel gets its own variable space, so there is no chance of collisions between different calls, and the variable is automatically trashed when the channel is hungup.
  • Environment variables provide a means to access unix environment variables from within Asterisk. There's a list further down this page.
If you define a channel variable with the same name as a global variable (and remember: user-defined variable names are not case sensitive), references to that variable name will return the value of the channel variable. For example, let us say that you define a context "FooTest" with a single extension, 100, with the following definition:(:smile:)

exten => 100,1,SetGlobalVar(FOO=5)
exten => 100,2,NoOp(${FOO})
exten => 100,3,NoOp(${foo})
exten => 100,4,SetVar(foo=8)
exten => 100,5,NoOp(${FOO})
exten => 100,6,NoOp(${foo})

(Note the use of the NoOp command to assist in debugging.) If you dial extension 100 in context FooTest, and you have Asterisk running with a verbose console, you will see output similar to the following:

— Executing SetGlobalVar("Zap/1-1", "FOO=5") in new stack
— Setting global variable 'FOO' to '5'
— Executing NoOp("Zap/1-1", "5") in new stack
— Executing NoOp("Zap/1-1", "5") in new stack
— Executing SetVar("Zap/1-1", "foo=8") in new stack
— Executing NoOp("Zap/1-1", "8") in new stack
— Executing NoOp("Zap/1-1", "8") in new stack

We discover that after the call to SetGlobalVar, ${FOO} and ${foo} returned the value of the global variable, giving the value 5. After the call to SetVar, the global variable "foo" was obscured by the channel variable "foo"; ${FOO} and ${foo} both gave the value 8. The value of the global variable remains unchanged at 5, however, and any other channels that refer to the global variable ${foo} would still get the value 5.

Inheritance of Channel Variables

Prepending a single _ character to a variables name in SetVar will cause that variable to be inherited by channels created by the main channel. eg. when using Dial(Local/...); once inherited these variables will not be further inherited. Prepending two _ characters will cause them to be inherited indefinitely.

Note that for retrieval purposes these variable names do not include the underscores.

exten => 100,1,SetVar(__FOO=5)
exten => 100,2,Dial(Local/test@CheckInherit)
exten => test,1,NoOp(${FOO})

will result in FOO being inherited. Without the underscores, the new local channel would start with a clean slate.


exten => 104,1,SetVar(FEE=fee)
exten => 104,2,SetVar(_FIE=fie)
exten => 104,3,SetVar(__FUM=fum)
exten => 104,4,Dial(Local/105)

exten => 105,1,NoOp(${FEE})
exten => 105,2,NoOp(${FIE})
exten => 105,3,NoOp(${FUM})
exten => 105,4,Dial(Local/106)

exten => 106,1,NoOp(${FEE})
exten => 106,2,NoOp(${FIE})
exten => 106,3,NoOp(${FUM})

results in

— Executing SetVar("SIP/oberon-365e", "FEE=fee") in new stack
— Executing SetVar("SIP/oberon-365e", "_FIE=fie") in new stack
— Executing SetVar("SIP/oberon-365e", "__FUM=fum") in new stack
— Executing Dial("SIP/oberon-365e", "Local/105") in new stack
— Called 105
— Executing NoOp("Local/105@default-7263,2", "") in new stack
— Executing NoOp("Local/105@default-7263,2", "fie") in new stack
— Executing NoOp("Local/105@default-7263,2", "fum") in new stack
— Executing Dial("Local/105@default-7263,2", "Local/106") in new stack
— Called 106
— Executing NoOp("Local/106@default-49be,2", "") in new stack
— Executing NoOp("Local/106@default-49be,2", "") in new stack
— Executing NoOp("Local/106@default-49be,2", "fum") in new stack

(This did not work correctly prior to the 1.2 release.)

Using $

If you want to set a global variable containing the another variable name in the [globals] category of extensions.conf you have to do something like this:


This way the MY_VAR value is ${EPOCH}-${EXTEN}.gsm

Using it with the EVAL() function is very useful. I.e. if you want to record you can do this:

exten => 104,1,SetVar(file=${EVAL(${MY_VAR})})
exten => 104,2,MixMonitor($The attachment id given is not valid.)

Predefined Channel Variables

There are some channel variables set by Asterisk that you can refer to in your dialplan definitions. Asterisk-defined variables, in contrast to user-defined variables, are case sensitive. Note: Several of these builtin variables have been converted to functions in 1.2, to allow setting their values.
  • ${ACCOUNTCODE}: Account code, if specified - see Asterisk billing (DEPRECATED in 1.2.0 and removed in 1.4. Use ${CDR(accountcode)}
  • ${ANSWEREDTIME}: This is the amount of time(in seconds) for actual call.
  • ${BLINDTRANSFER}: The active SIP channel that dialed the number. This will return the SIP Channel that dialed the number when doing blind transfers - see BLINDTRANSFER
  • ${CALLERID(all)}: The current Caller ID name and number - See Setting Callerid for usage in Asterisk 1.4
  • ${CALLERID(name)}: The current Caller ID name - ${CALLERIDNAME} was used in versions of Asterisk prior to 1.2.0, it was DEPRECATED in 1.2.0 and removed in 1.4.
  • ${CALLERID(num)}: The current Caller ID number - ${CALLERIDNUM} was used in versions of Asterisk prior to 1.2.0, it was DEPRECATED in 1.2.0 and removed in 1.4.
(Note: this is not necessarily numeric as the name would indicate and can legitimately contain the space character. Commands acting on this variable (such as 'GotoIf', for example) should be aware of this).
  • ${CALLINGPRES}: PRI Call ID Presentation variable for incoming calls (See callingpres )
  • ${CHANNEL}: Current channel name
  • ${CONTEXT}: The name of the current context
  • ${DATETIME}: Current date time in the format: DDMMYYYY-HH:MM:SS This is deprecated in Asterisk 1.2, instead use :${STRFTIME(${EPOCH},,%d%mNaVH:NaVS)})
  • ${DIALEDPEERNAME}: Name of the called party. Broken for now, see DIALEDPEERNAME
  • ${DIALEDPEERNUMBER}: Number of the called party. Broken for now, see DIALEDPEERNUMBER
  • ${DIALEDTIME}: Time since the number was dialed (only works when dialed party answers the line?!)
  • ${DIALSTATUS}: Status of the call. See DIALSTATUS (note: In the current SVN release, DIALSTATUS seems to have been removed. Now you should use the DEVSTATE function. Try in astersisk console "core show function DEVSTATE" for more informations)
  • ${DNID}: Dialed Number Identifier. Limitations apply, see DNID
  • ${EPOCH}: The current UNIX-style epoch (number of seconds since 1 Jan 1970)
  • ${EXTEN}: The current extension
  • ${HANGUPCAUSE}: The last hangup return code on a Zap channel connected to a PRI interface
  • ${INVALID_EXTEN}: The extension asked for when redirected to the i (invalid) extension
  • ${LANGUAGE}: The current language setting. See Asterisk multi-language
  • ${MEETMESECS}: Number of seconds a user participated in a MeetMe conference
  • ${PRIORITY}: The current priority
  • ${RDNIS}: The current redirecting DNIS, Caller ID that redirected the call. Limitations apply, see RDNIS
  • ${SIPDOMAIN}: SIP destination domain of an inbound call (if appropriate)
  • ${SIP_CODEC}: Used to set the SIP codec for a call (apparently broken in Ver 1.0.1, ok in Ver. 1.0.3 & 1.0.4, not sure about 1.0.2)
  • ${SIPCALLID}: The SIP dialog Call-ID: header
  • ${SIPUSERAGENT}: The SIP user agent header
  • ${TIMESTAMP}: Current date time in the format: YYYYMMDD-HHMMSS This is deprecated as of Asterisk 1.4, instead use :${STRFTIME(${EPOCH},,%Y%m%d-%H%M%S)})
  • ${TRANSFERCAPABILITY}: Type of Channel
  • ${TXTCIDNAME}: Result of application TXTCIDName (see below)
  • ${UNIQUEID}: Current call unique identifier
  • ${TOUCH_MONITOR}: used for "one touch record" (see features.conf, and wW dial flags). If is set on either side of the call then that var contains the app_args for app_monitor otherwise the default of WAV||m is used

Application-specific variables

Some applications take extra input or provide output using channel variables.
  • AgentCallbackLogin returns ${AGENTBYCALLERID_${CALLERID}}: The ID of the agent successfully logged on.
  • ChanIsAvail returns ${AVAILCHAN}: The first available channel
  • Dial takes input from ${VXML_URL}: Send XML Url to Cisco 7960 or to i6net VoiceXML browser
  • Dial takes input from ${ALERT_INFO}: Set ring cadence or allow intercom on for various SIP phones
  • Dial returns ${CAUSECODE}: If the dial failed, this is the errormessage
  • Dial returns ${DIALSTATUS}: Text code returning status of last dial attempt.
  • Dial takes input from ${TRANSFER_CONTEXT}: If this variable exists, when a #transfer is executed it goes to the selected extension on this context.
  • EnumLookup returns ${ENUM}: The result of the lookup
  • Hangup reads the ${PRI_CAUSE} variable for setting PRI return codes
  • MeetMe takes input from {MEETME_AGI_BACKGROUND}: An AGI script to run
  • MeetMe returns ${MEETMESECS}: The number of seconds the user was in a conference
  • Playback returns ${PLAYBACKSTATUS}: The status of the command (FAILED|SUCCESS)
  • Queue returns ${QUEUESTATUS}: The reason for popping the call out of the queue
  • TXTCIDName returns ${TXTCIDNAME}: The result of the DNS lookup
  • VoiceMail returns ${VMSTATUS}: indicates the status of the execution of the VoiceMail application. Possible values are: SUCCESS | USEREXIT | FAILED .

Macro-specific variables

When in a macro context, extra channel variables are available.
  • ${ARG1}: The first argument passed to the macro
  • ${ARG2}: The second argument passed to the macro (and so on)
  • ${MACRO_CONTEXT}: The context of the extension that triggered this macro
  • ${MACRO_EXTEN}: The extension that triggered this macro
  • ${MACRO_OFFSET}: Set by a macro to influence the priority where execution will continue after exiting the macro
  • ${MACRO_PRIORITY}: The priority in the extension where this macro was triggered

Environment Variables

You may access unix environment variables using the syntax:


  • ${ENV(ASTERISK_PROMPT)}: the current Asterisk CLI prompt.
  • ${ENV(RECORDED_FILE)}: the filename of the last file saved by the Record command (available in CVS > 2004-03-21)

String Handling Functions

String Length


returns the length of the string foo. For example,

exten => 100,1,SetVar(Fruit=pear)
exten => 100,2,NoOp(${LEN(Fruit)})
exten => 100,3,NoOp(${LEN(${Fruit})})

The first NoOp would show a value of 5 (the length of the string "fruit"). The second NoOp would show a value of 4 (the length of the string "pear").

This is an excellent way to check for a NULL or empty string.



returns a substring of the string foo, beginning at offset offset and returning the next length characters. The first character is at offset 0.
  • If offset is negative, it is taken leftwards from the right hand end of the string.
  • If length is omitted or is negative, then all the rest of the string beginning at offset is returned.


${123456789:1} - returns the string 23456789
${123456789:-4} - returns the string 6789
${123456789:0:3} - returns the string 123
${123456789:2:3} - returns the string 345
${123456789:-4:3} - returns the string 678

Examples of use:

exten => _NXX.,1,SetVar(areacode=${EXTEN:0:3}) - get the first 3 digits of ${EXTEN}
exten => _516XXXXXXX,1,Dial(${EXTEN:3}) - get all but the first 3 digits of ${EXTEN}
exten => 100,1,SetVar(whichVowel=4)

exten => 100,2,SetVar(foo=AEIOU:${whichVowel}:1) - sets ${foo} to the single letter 'U'

String Concatenation

To concatenate two strings, simply write them together:


Variable math

To perform math on variables e.g. increment, multiplication, addition simply write:

exten => s,1,SetVar(SOMEVAR=$[${SOMEVAR} + 1]) ; increment
exten => s,2,SetVar(SOMEVAR=$[2 * ${SOMEVAR}]) ; multiplication etc...
In times past, a single space was required between items in the $[...] expressions. This is no longer the case!

In late model Asterisks (1.2?), the MATH function is also available...

exten => s,1,Set(SOMEVAR=${MATH(${SOMEVAR}+1)}) ; increment
exten => s,2,Set(SOMEVAR=${MATH(2*${SOMEVAR})}) ; multiplication etc...

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