----------------------------
Asterisk dial plan variables 
----------------------------

There are two levels of parameter evaluation done in the Asterisk
dial plan in extensions.conf.
* The first, and most frequently used, is the substitution of variable
  references with their values. 
* Then there are the evaluations of expressions done in $[ .. ]. 
  This will be discussed below.

Asterisk has user-defined variables and standard variables set
by various modules in Asterisk. These standard variables are
listed at the end of this document.

___________________________
PARAMETER QUOTING: 
---------------------------

exten => s,5,BackGround,blabla

The parameter (blabla) can be quoted ("blabla"). In this case, a 
comma does not terminate the field. However, the double quotes
will be passed down to the Background command, in this example.

Also, characters special to variable substitution, expression evaluation, etc
(see below), can be quoted. For example, to literally use a $ on the 
string "$1231", quote it with a preceding \. Special characters that must
be quoted to be used, are [ ] $ " \. (to write \ itself, use \\). 

These Double quotes and escapes are evaluated at the level of the
asterisk config file parser. 

Double quotes can also be used inside expressions, as discussed below.

___________________________
VARIABLES: 
---------------------------

Parameter strings can include variables. Variable names are arbitrary strings. 
They are stored in the respective channel structure. 

To set a variable to a particular value, do : 

    exten => 1,2,Set(varname=value)

You can substitute the value of a variable everywhere using ${variablename}.
For example, to stringwise append $lala to $blabla and store result in $koko, 
do: 

   exten => 1,2,Set(koko=${blabla}${lala})


There are two reference modes - reference by value and reference by name. 
To refer to a variable with its name (as an argument to a function that 
requires a variable), just write the name. To refer to the variable's value, 
enclose it inside ${}. For example, Set takes as the first argument 
(before the =) a variable name, so: 

	exten => 1,2,Set(koko=lala)
	exten => 1,3,Set(${koko}=blabla)

stores to the variable "koko" the value "lala" and to variable "lala" the 
value "blabla". 

In fact, everything contained ${here} is just replaced with the value of 
the variable "here". 

____________________
VARIABLE INHERITANCE
--------------------

Variable names which are prefixed by "_" will be inherited to channels 
that are created in the process of servicing the original channel in 
which the variable was set.  When the inheritance takes place, the 
prefix will be removed in the channel inheriting the variable.  If the 
name is prefixed by "__" in the channel, then the variable is 
inherited and the "__" will remain intact in the new channel.

In the dialplan, all references to these variables refer to the same 
variable, regardless of having a prefix or not.  Note that setting any 
version of the variable removes any other version of the variable, 
regardless of prefix.

Example:

Set(__FOO=bar) ; Sets an inherited version of "FOO" variable 
Set(FOO=bar)   ; Removes the inherited version and sets a local 
               ; variable.

However,

NoOp(${__FOO}) is identical to NoOp(${FOO})



___________________________________
SELECTING CHARACTERS FROM VARIABLES
-----------------------------------

The format for selecting characters from a variable can be expressed as:

	${variable_name[:offset[:length]]}

If you want to select the first N characters from the string assigned
to a variable, simply append a colon and the number of characters to
skip from the beginning of the string to the variable name.

	;Remove the first character of extension, save in "number" variable
	exten => _9X.,1,Set(number=${EXTEN:1})

Assuming we've dialed 918005551234, the value saved to the 'number' variable
would be 18005551234. This is useful in situations when we require users to 
dial a number to access an outside line, but do not wish to pass the first 
digit.

If you use a negative offset number, Asterisk starts counting from the end 
of the string and then selects everything after the new position. The following
example will save the numbers 1234 to the 'number' variable, still assuming
we've dialed 918005551234.

	;Remove everything before the last four digits of the dialed string
	exten => _9X.,1,Set(number=${EXTEN:-4})

We can also limit the number of characters from our offset position that we
wish to use. This is done by appending a second colon and length value to the
variable name. The following example will save the numbers 555 to the 'number'
variable.

	;Only save the middle numbers 555 from the string 918005551234
	exten => _9X.,1,Set(number=${EXTEN:5:3})

The length value can also be used in conjunction with a negative offset. This
may be useful if the length of the string is unknown, but the trailing digits
are. The following example will save the numbers 555 to the 'number' variable,
even if the string starts with more characters than expected (unlike the
previous example).

	;Save the numbers 555 to the 'number' variable
	exten => _9X.,1,Set(number=${EXTEN:-7:3})

If a negative length value is entered, it is ignored and Asterisk will match
to the end of the string.
___________________________
EXPRESSIONS: 
---------------------------

Everything contained inside a bracket pair prefixed by a $ (like $[this]) is 
considered as an expression and it is evaluated. Evaluation works similar to 
(but is done on a later stage than) variable substitution: the expression 
(including the square brackets) is replaced by the result of the expression 
evaluation. 

For example, after the sequence: 

exten => 1,1,Set(lala=$[1 + 2])
exten => 1,2,Set(koko=$[2 * ${lala}])

the value of variable koko is "6".

and, further:

exten => 1,1,Set,(lala=$[  1 +    2   ]);

will parse as intended. Extra spaces are ignored.


______________________________
SPACES INSIDE VARIABLE VALUES
------------------------------
If the variable being evaluated contains spaces, there can be problems.

For these cases, double quotes around text that may contain spaces
will force the surrounded text to be evaluated as a single token.
The double quotes will be counted as part of that lexical token.

As an example:

exten => s,6,GotoIf($[ "${CALLERIDNAME}" : "Privacy Manager" ]?callerid-liar|s|1:s|7)

The variable CALLERIDNAME could evaluate to "DELOREAN MOTORS" (with a space)
but the above will evaluate to:

"DELOREAN MOTORS" : "Privacy Manager"

and will evaluate to 0.

The above without double quotes would have evaluated to:

DELOREAN MOTORS : Privacy Manager

and will result in syntax errors, because token DELOREAN is immediately
followed by token MOTORS and the expression parser will not know how to 
evaluate this expression, because it does not match its grammar.

_____________________
OPERATORS
---------------------
Operators are listed below in order of increasing precedence.  Operators
with equal precedence are grouped within { } symbols.

     expr1 | expr2
             Return the evaluation of expr1 if it is neither an empty string
             nor zero; otherwise, returns the evaluation of expr2.

     expr1 & expr2
             Return the evaluation of expr1 if neither expression evaluates to
             an empty string or zero; otherwise, returns zero.

     expr1 {=, >, >=, <, <=, !=} expr2
             Return the results of integer comparison if both arguments are
             integers; otherwise, returns the results of string comparison
             using the locale-specific collation sequence.  The result of each
             comparison is 1 if the specified relation is true, or 0 if the
             relation is false.

     expr1 {+, -} expr2
             Return the results of addition or subtraction of integer-valued
             arguments.

     expr1 {*, /, %} expr2
             Return the results of multiplication, integer division, or
             remainder of integer-valued arguments.

     - expr1
            Return the result of subtracting expr1 from 0.
            This, the unary minus operator, is right associative, and
            has the same precedence as the ! operator.

     ! expr1
            Return the result of a logical complement of expr1.
            In other words, if expr1 is null, 0, an empty string,
            or the string "0", return a 1. Otherwise, return a 0.
            It has the same precedence as the unary minus operator, and
            is also right associative.

     expr1 : expr2
             The `:' operator matches expr1 against expr2, which must be a
             regular expression.  The regular expression is anchored to the
             beginning of  the string with an implicit `^'.

             If the match succeeds and the pattern contains at least one regu-
             lar expression subexpression `\(...\)', the string correspond-
             ing to `\1' is returned; otherwise the matching operator
             returns the number of characters matched.  If the match fails and
             the pattern contains a regular expression subexpression the null
             string is returned; otherwise 0.

             Normally, the double quotes wrapping a string are left as part
             of the string. This is disastrous to the : operator. Therefore,
             before the regex match is made, beginning and ending double quote
             characters are stripped from both the pattern and the string.

      expr1 =~ expr2
             Exactly the same as the ':' operator, except that the match is
             not anchored to the beginning of the string. Pardon any similarity
             to seemingly similar operators in other programming languages!
             The ":" and "=~" operators share the same precedence.

      expr1 ? expr2 :: expr3
             Traditional Conditional operator. If expr1 is a number
	     that evaluates to 0 (false), expr3 is result of the this
	     expression evaluation.  Otherwise, expr2 is the result.
	     If expr1 is a string, and evaluates to an empty string,
	     or the two characters (""), then expr3 is the
	     result. Otherwise, expr2 is the result.  In Asterisk, all
	     3 exprs will be "evaluated"; if expr1 is "true", expr2
	     will be the result of the "evaluation" of this
	     expression.  expr3 will be the result otherwise. This
	     operator has the lowest precedence.

Parentheses are used for grouping in the usual manner.

Operator precedence is applied as one would expect in any of the C
or C derived languages.

Examples

 "One Thousand Five Hundred" =~ "(T[^ ]+)"
	returns: Thousand

 "One Thousand Five Hundred" =~ "T[^ ]+"
	returns: 8

 "One Thousand Five Hundred" : "T[^ ]+"
	returns: 0

 "8015551212" : "(...)"
	returns: 801

 "3075551212":"...(...)"
	returns: 555

 ! "One Thousand Five Hundred" =~ "T[^ ]+"
	returns: 0 (because it applies to the string, which is non-null,
                    which it turns to "0", and then looks for the pattern
                    in the "0", and doesn't find it)

 !( "One Thousand Five Hundred" : "T[^ ]+" )
	returns: 1  (because the string doesn't start with a word starting
                     with T, so the match evals to 0, and the ! operator
                     inverts it to 1 ).

 2 + 8 / 2
	returns 6. (because of operator precedence; the division is done first, then the addition).

 2+8/2
	returns 6. Spaces aren't necessary.

(2+8)/2
	returns 5, of course.

Of course, all of the above examples use constants, but would work the
same if any of the numeric or string constants were replaced with a
variable reference ${CALLERIDNUM}, for instance.

__________________________
NUMBERS VS STRINGS
--------------------------

Tokens consisting only of numbers are converted to 64-bit numbers for
most of the operators. This means that overflows can occur when the
numbers get above 18 digits.  Warnings will appear in the logs in this
case.
___________________________
CONDITIONALS
---------------------------

There is one conditional application - the conditional goto : 

	exten => 1,2,gotoif(condition?label1:label2)

If condition is true go to label1, else go to label2. Labels are interpreted
exactly as in the normal goto command.

"condition" is just a string. If the string is empty or "0", the condition
is considered to be false, if it's anything else, the condition is true. 
This is designed to be used together with the expression syntax described 
above, eg : 

	exten => 1,2,gotoif($[${CALLERID} = 123456]?2|1:3|1)

Example of use : 

exten => s,2,Set(vara=1)
exten => s,3,Set(varb=$[${vara} + 2])
exten => s,4,Set(varc=$[${varb} * 2])
exten => s,5,GotoIf($[${varc} = 6]?99|1:s|6)

___________________________
PARSE ERRORS
---------------------------

Syntax errors are now output with 3 lines.

If the extensions.conf file contains a line like:

exten => s,6,GotoIf($[ "${CALLERIDNUM}"  = "3071234567" & &  "${CALLERIDNAME}" : "Privacy Manager" ]?callerid-liar|s|1:s|7)

You may see an error in /var/log/asterisk/messages like this:

Jul 15 21:27:49 WARNING[1251240752]: ast_yyerror(): syntax error: parse error, unexpected TOK_AND, expecting TOK_MINUS or TOK_LP or TOKEN; Input:
"3072312154"  = "3071234567" & & "Steves Extension" : "Privacy Manager" 
                               ^

The log line tells you that a syntax error was encountered. It now
also tells you (in grand standard bison format) that it hit an "AND"
(&) token unexpectedly, and that was hoping for for a MINUS (-), LP
(left parenthesis), or a plain token (a string or number).

The next line shows the evaluated expression, and the line after
that, the position of the parser in the expression when it became confused,
marked with the "^" character.

___________________________
NULL STRINGS
---------------------------

Testing to see if a string is null can be done in one of two different ways:

	exten => _XX.,1,GotoIf($["${calledid}" != ""]?3) 

	exten => _XX.,1,GotoIf($[foo${calledid} != foo]?3) 


The second example above is the way suggested by the WIKI. It will 
work as long as there are no spaces in the evaluated value.

The first way should work in all cases, and indeed, might now
be the safest way to handle this situation.

___________________________
WARNING
---------------------------

If you need to do complicated things with strings, asterisk expressions
is most likely NOT the best way to go about it. AGI scripts are an
excellent option to this need, and make available the full power of
whatever language you desire, be it Perl, C, C++, Cobol, RPG, Java,
Snobol, PL/I, Scheme, Common Lisp, Shell scripts, Tcl, Forth, Modula,
Pascal, APL, assembler, etc.

----------------------------
INCOMPATIBILITIES
----------------------------

The asterisk expression parser has undergone some evolution. It is hoped
that the changes will be viewed as positive. 

The "original" expression parser had a simple, hand-written scanner,
and a simple bison grammar. This was upgraded to a more involved bison
grammar, and a hand-written scanner upgraded to allow extra spaces,
and to generate better error diagnostics. This upgrade required bison
1.85, and part of the user community felt the pain of having to
upgrade their bison version.

The next upgrade included new bison and flex input files, and the makefile
was upgraded to detect current version of both flex and bison, conditionally
compiling and linking the new files if the versions of flex and bison would
allow it.

If you have not touched your extensions.conf files in a year or so, the
above upgrades may cause you some heartburn in certain circumstances, as
several changes have been made, and these will affect asterisk's behavior on 
legacy extension.conf constructs.  The changes have been engineered
to minimize these conflicts, but there are bound to be problems.

The following list gives some (and most likely, not all) of areas
of possible concern with "legacy" extension.conf files:

1. Tokens separated by space(s).
   Previously, tokens were separated by spaces. Thus, ' 1 + 1 ' would evaluate
   to the value '2', but '1+1' would evaluate to the string '1+1'. If this
   behavior was depended on, then the expression evaluation will break. '1+1'
   will now evaluate to '2', and something is not going to work right.
   To keep such strings from being evaluated, simply wrap them in double 
   quotes: '  "1+1" '

2. The colon operator. In versions previous to double quoting, the
   colon operator takes the right hand string, and using it as a 
   regex pattern, looks for it in the left hand string. It is given
   an implicit ^ operator at the beginning, meaning the pattern 
   will match only at the beginning of the left hand string. 
   If the pattern or the matching string had double quotes around
   them, these could get in the way of the pattern match. Now,
   the wrapping double quotes are stripped from both the pattern 
   and the left hand string before applying the pattern. This
   was done because it recognized that the new way of
   scanning the expression doesn't use spaces to separate tokens,
   and the average regex expression is full of operators that 
   the scanner will recognize as expression operators. Thus, unless
   the pattern is wrapped in double quotes, there will be trouble.
   For instance,      ${VAR1} : (Who|What*)+
   may have have worked before, but unless you wrap the pattern
   in double quotes now, look out for trouble! This is better:
         "${VAR1}" : "(Who|What*)+"
   and should work as previous.

3. Variables and Double Quotes
   Before these changes, if a variable's value contained one or more double
   quotes, it was no reason for concern. It is now!

4. LE, GE, NE operators removed. The code supported these operators,
   but they were not documented. The symbolic operators, <=, >=, and !=
   should be used instead.

5.  Added the unary '-' operator. So you can 3+ -4 and get -1.

6.  Added the unary '!' operator, which is a logical complement.
    Basically, if the string or number is null, empty, or '0',
    a '1' is returned. Otherwise a '0' is returned.

7.  Added the '=~' operator, just in case someone is just looking for
    match anywhere in the string. The only diff with the ':' is that
    match doesn't have to be anchored to the beginning of the string.

8.  Added the conditional operator  'expr1 ? true_expr :: false_expr'
    First, all 3 exprs are evaluated, and if expr1 is false, the 'false_expr'
    is returned as the result. See above for details. 

9.  Unary operators '-' and '!' were made right associative.

--------------------------------------------------------
DEBUGGING HINTS FOR $[  ]  EXPRESSIONS
--------------------------------------------------------

There are two utilities you can build to help debug the $[ ] in
your extensions.conf file.

The first, and most simplistic, is to issue the command:

make testexpr2

in the top level asterisk source directory. This will build a small
executable, that is able to take the first command line argument, and
run it thru the expression parser. No variable substitutions will be
performed. It might be safest to wrap the expression in single
quotes...

testexpr2 '2*2+2/2'

is an example.

And, in the utils directory, you can say:

make check_expr

and a small program will be built, that will check the file mentioned
in the first command line argument, for any expressions that might be
have problems when you move to flex-2.5.31.  It was originally
designed to help spot possible incompatibilities when moving from the
pre-2.5.31 world to the upgraded version of the lexer.

But one more capability has been added to check_expr, that might make
it more generally useful. It now does a simple minded evaluation of
all variables, and then passes the $[] exprs to the parser. If there
are any parse errors, they will be reported in the log file. You can
use check_expr to do a quick sanity check of the expressions in your
extensions.conf file, to see if they pass a crude syntax check.

The "simple-minded" variable substitution replaces ${varname} variable
references with '555'. You can override the 555 for variable values,
by entering in var=val arguments after the filename on the command
line.  So...

 check_expr /etc/asterisk/extensions.conf CALLERIDNUM=3075551212 DIALSTATUS=TORTURE EXTEN=121

will substitute any ${CALLERIDNUM} variable references with
3075551212, any ${DIALSTATUS} variable references with 'TORTURE', and
any ${EXTEN} references with '121'.  If there is any fancy stuff
going on in the reference, like ${EXTEN:2}, then the override will
not work. Everything in the ${...} has to match. So, to substitute
#{EXTEN:2} references, you'd best say:

 check_expr /etc/asterisk/extensions.conf CALLERIDNUM=3075551212 DIALSTATUS=TORTURE EXTEN:2=121

on stdout, you will see something like:

 OK -- $[ "${DIALSTATUS}"  = "TORTURE" | "${DIALSTATUS}" = "DONTCALL" ] at line 416

In the expr2_log file that is generated, you will see:

 line 416, evaluation of $[  "TORTURE"  = "TORTURE" | "TORTURE" = "DONTCALL"  ] result: 1

check_expr is a very simplistic algorithm, and it is far from being
guaranteed to work in all cases, but it is hoped that it will be
useful.

---------------------------------------------------------
Asterisk standard channel variables 
---------------------------------------------------------
There are a number of variables that are defined or read
by Asterisk. Here is a list of them. More information is
available in each application's help text. All these variables
are in UPPER CASE only.

Variables marked with a * are builtin functions and can't be set,
only read in the dialplan.  Writes to such variables are silently 
ignored.

${ACCOUNTCODE} 	 	* Account code (if specified) (Deprecated; use ${CDR(accountcode)})
${BLINDTRANSFER} 	The name of the channel on the other side of a blind transfer
${BRIDGEPEER}	 	Bridged peer
${CALLERANI}	 	* Caller ANI (PRI channels) (Deprecated; use ${CALLERID(ani)})
${CALLERID}	 	* Caller ID (Deprecated; use ${CALLERID(all)})
${CALLERIDNAME}	 	* Caller ID Name only (Deprecated; use ${CALLERID(name)})
${CALLERIDNUM}	 	* Caller ID Number only (Deprecated; use ${CALLERID(num)})
${CALLINGANI2}	 	* Caller ANI2 (PRI channels)
${CALLINGPRES}	 	* Caller ID presentation for incoming calls (PRI channels)
${CALLINGTNS} 	 	* Transit Network Selector (PRI channels)
${CALLINGTON}    	* Caller Type of Number (PRI channels)
${CHANNEL}	 	* Current channel name
${CONTEXT}       	* Current context
${DATETIME}	 	* Current date time in the format: DDMMYYYY-HH:MM:SS (Deprecated; use ${STRFTIME(${EPOCH},,%d%m%Y-%H:%M:%S)})
${DB_RESULT}		Result value of DB_EXISTS() dial plan function
${DNID}          	* Dialed Number Identifier (Deprecated; use ${CALLERID(dnid)})
${EPOCH}	 	* Current unix style epoch
${EXTEN}	 	* Current extension
${ENV(VAR)}	 	Environmental variable VAR
${GOTO_ON_BLINDXFR}	Transfer to the specified context/extension/priority
			after a blind transfer (use ^ characters in place of
			| to separate context/extension/priority when setting
			this variable from the dialplan)
${HANGUPCAUSE}	 	* Asterisk cause of hangup (inbound/outbound)
${HINT}          	* Channel hints for this extension
${HINTNAME}      	* Suggested Caller*ID name for this extension
${INVALID_EXTEN} 	The invalid called extension (used in the "i" extension)
${LANGUAGE}	 	* Current language (Deprecated; use ${LANGUAGE()})
${LEN(VAR)}	 	* String length of VAR (integer)
${PRIORITY}	 	* Current priority in the dialplan
${PRIREDIRECTREASON} 	Reason for redirect on PRI, if a call was directed
${RDNIS}         	* Redirected Dial Number ID Service (Deprecated; use ${CALLERID(rdnis)})
${TIMESTAMP}	 	* Current date time in the format: YYYYMMDD-HHMMSS (Deprecated; use ${STRFTIME(${EPOCH},,%Y%m%d-%H%M%S)})
${TRANSFER_CONTEXT} 	Context for transferred calls
${UNIQUEID}	 	* Current call unique identifier

Application return values
-------------------------
In Asterisk 1.2, many applications return the result in a variable
instead of, as in Asterisk 1.0, changing the dial plan priority (+101).
For the various status values, see each application's help text.

${AQMSTATUS}			* addqueuemember()
${AVAILSTATUS}			* chanisavail()
${CHECKGROUPSTATUS}		* checkgroup()
${CHECKMD5STATUS}		* checkmd5()
${CPLAYBACKSTATUS}		* controlplayback()
${DIALSTATUS}   		* dial()
${DBGETSTATUS}			* dbget()
${ENUMSTATUS}			* enumlookup()
${HASVMSTATUS}			* hasnewvoicemail()
${LOOKUPBLSTATUS}		* lookupblacklist()
${OSPLOOKUPSTATUS}		* osplookup()
${OSPNEXTSTATUS}		* ospnext()
${OSPFINISHSTATUS}		* ospfinish()
${PLAYBACKSTATUS}		* playback()
${PQMSTATUS}			* pausequeuemember()
${PRIVACYMGRSTATUS}		* privacymanager()
${QUEUESTATUS}			* queue()
${RQMSTATUS}			* removequeuemember()
${SENDIMAGESTATUS}		* sendimage()
${SENDTEXTSTATUS}		* sendtext()
${SENDURLSTATUS}		* sendurl()
${SIPGETSTATUS}			* sipgetheader()
${SYSTEMSTATUS}			* system()
${TRANSFERSTATUS}		* transfer()
${TXTCIDNAMESTATUS}		* txtcidname()
${UPQMSTATUS}			* unpausequeuemember()
${VMSTATUS}			* voicmail()
${VMBOXEXISTSSTATUS}		* vmboxexists()
${WAITSTATUS}			* waitforsilence()


Various application variables
-----------------------------
${CURL}			* Resulting page content for curl()
${ENUM}			* Result of application EnumLookup
${EXITCONTEXT}		Context to exit to in IVR menu (app background())
			or in the RetryDial() application
${MONITOR}		* Set to "TRUE" if the channel is/has been monitored (app monitor())
${MONITOR_EXEC}		Application to execute after monitoring a call
${MONITOR_EXEC_ARGS}	Arguments to application
${MONITOR_FILENAME} 	File for monitoring (recording) calls in queue
${QUEUE_PRIO}		Queue priority
${QUEUESTATUS} 		Status of the call, one of:
			(TIMEOUT | FULL | JOINEMPTY | LEAVEEMPTY | JOINUNAVAIL | LEAVEUNAVAIL)
${RECORDED_FILE} 	* Recorded file in record()
${TALK_DETECTED} 	* Result from talkdetect()
${TOUCH_MONITOR} 	The filename base to use with Touch Monitor (auto record)
${TOUCH_MONITOR_FORMAT} The audio format to use with Touch Monitor (auto record)
${TXTCIDNAME}		* Result of application TXTCIDName
${VPB_GETDTMF}		chan_vpb

The MeetMe Conference Bridge uses the following variables:
----------------------------------------------------------
${MEETME_RECORDINGFILE} 	Name of file for recording a conference with 
				the "r" option
${MEETME_RECORDINGFORMAT} 	Format of file to be recorded
${MEETME_EXIT_CONTEXT} 		Context for exit out of meetme meeting
${MEETME_AGI_BACKGROUND} 	AGI script for Meetme (zap only)
${MEETMESECS} 			* Number of seconds a user participated in a MeetMe conference

The VoiceMail() application uses the following variables:
---------------------------------------------------------
${VM_CATEGORY}		Sets voicemail category
${VM_NAME}		* Full name in voicemail
${VM_DUR}		* Voicemail duration
${VM_MSGNUM}		* Number of voicemail message in mailbox
${VM_CALLERID}		* Voicemail Caller ID (Person leaving vm)
${VM_CIDNAME}		* Voicemail Caller ID Name
${VM_CIDNUM}		* Voicemail Caller ID Number
${VM_DATE}		* Voicemail Date
${VM_MESSAGEFILE}	* Path to message left by caller

The VMAuthenticate() application uses the following variables:
---------------------------------------------------------
${AUTH_MAILBOX}	* Authenticated mailbox
${AUTH_CONTEXT}	* Authenticated mailbox context

DUNDiLookup() uses the following variables
---------------------------------------------------------
${DUNDTECH}	* The Technology of the result from a call to DUNDiLookup()
${DUNDDEST}	* The Destination of the result from a call to DUNDiLookup()

The Zaptel channel sets the following variables:
---------------------------------------------------------
${ANI2}			* The ANI2 Code provided by the network on the incoming call. 
			(ie, Code 29 identifies call as a Prison/Inmate Call)
${CALLTYPE}		* Type of call (Speech, Digital, etc)
${CALLEDTON}		* Type of number for incoming PRI extension
			i.e. 0=unknown, 1=international, 2=domestic, 3=net_specific, 
			4=subscriber, 6=abbreviated, 7=reserved 
${CALLINGSUBADDR}	* Called PRI Subaddress
${FAXEXTEN}	 	* The extension called before being redirected to "fax"	
${PRIREDIRECTREASON}	* Reason for redirect, if a call was directed

The SIP channel uses the following variables:
---------------------------------------------------------
${SIPCALLID} 		* SIP Call-ID: header verbatim (for logging or CDR matching)
${SIPDOMAIN}    	* SIP destination domain of an inbound call (if appropriate)
${SIPUSERAGENT} 	* SIP user agent 
${SIPURI}		* SIP uri
${SIP_CODEC} 		Set the SIP codec for a call	
${SIP_URI_OPTIONS}	* additional options to add to the URI for an outgoing call

The Agent channel uses the following variables:
---------------------------------------------------------
${AGENTMAXLOGINTRIES}	Set the maximum number of failed logins
${AGENTUPDATECDR}	Whether to update the CDR record with Agent channel data
${AGENTGOODBYE}		Sound file to use for "Good Bye" when agent logs out
${AGENTACKCALL} 	Whether the agent should acknowledge the incoming call
${AGENTAUTOLOGOFF}	Auto logging off for an agent
${AGENTWRAPUPTIME}	Setting the time for wrapup between incoming calls
${AGENTNUMBER}		* Agent number (username) set at login
${AGENTSTATUS}		* Status of login	( fail | on | off )
${AGENTEXTEN}		* Extension for logged in agent

The Dial() application uses the following variables:
---------------------------------------------------------
${DIALEDPEERNAME} 		* Dialed peer name
${DIALEDPEERNUMBER} 		* Dialed peer number
${DIALEDTIME}   		* Time for the call (seconds)
${ANSWEREDTIME} 		* Time from dial to answer (seconds)
${DIALSTATUS}   		* Status of the call, one of:
                		(CHANUNAVAIL | CONGESTION | BUSY | NOANSWER 
					| ANSWER | CANCEL | DONTCALL | TORTURE)
${DYNAMIC_FEATURES}		* The list of features (from the [applicationmap] section of
				  features.conf) to activate during the call, with feature
				  names separated by '#' characters
${LIMIT_PLAYAUDIO_CALLER}	Soundfile for call limits
${LIMIT_PLAYAUDIO_CALLEE}	Soundfile for call limits
${LIMIT_WARNING_FILE}		Soundfile for call limits
${LIMIT_TIMEOUT_FILE}		Soundfile for call limits
${LIMIT_CONNECT_FILE}		Soundfile for call limits
${OUTBOUND_GROUP}		Default groups for peer channels (as in SetGroup)
* See "show application dial" for more information

The chanisavail() application sets the following variables:
-----------------------------------------------------------
${AVAILCHAN}		* the name of the available channel if one was found	
${AVAILORIGCHAN} 	* the canonical channel name that was used to create the channel
${AVAILSTATUS}		* Status of requested channel

When using macros in the dialplan, these variables are available
---------------------------------------------------------
${MACRO_EXTEN}		* The calling extensions
${MACRO_CONTEXT}	* The calling context
${MACRO_PRIORITY}	* The calling priority
${MACRO_OFFSET}		Offset to add to priority at return from macro

If you compile with OSP support in the SIP channel, these
variables are used:
---------------------------------------------------------
${OSPHANDLE}		Handle from the OSP Library
${OSPTECH}		OSP Technology from Library
${OSPDEST}		OSP Destination from Library
${OSPTOKEN}		OSP Token to use for call from Library
${OSPRESULTS}		Number of OSP results

____________________________________
CDR Variables
------------------------------------

If the channel has a cdr, that cdr record has it's own set of variables which 
can be accessed just like channel variables. The following builtin variables
are available.

${CDR(clid)}			Caller ID
${CDR(src)}			Source 
${CDR(dst)}			Destination
${CDR(dcontext)}		Destination context
${CDR(channel)}			Channel name
${CDR(dstchannel)}		Destination channel
${CDR(lastapp)}			Last app executed
${CDR(lastdata)}		Last app's arguments
${CDR(start)}			Time the call started.
${CDR(answer)}			Time the call was answered.
${CDR(end)}			Time the call ended.
${CDR(duration)}		Duration of the call.
${CDR(billsec)}			Duration of the call once it was answered.
${CDR(disposition)}		ANSWERED, NO ANSWER, BUSY
${CDR(amaflags)}		DOCUMENTATION, BILL, IGNORE etc
${CDR(accountcode)}		The channel's account code.
${CDR(uniqueid)}		The channel's unique id.
${CDR(userfield)}		The channels uses specified field.


In addition, you can set your own extra variables with a traditional
Set(CDR(var)=val) to anything you want.

Certain functional variables may be accessed with ${foo(<args>)}.  A list
of these functional variables may be found by typing "show functions"
at the Asterisk CLI.
