README.variables

----------------------------
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.

NOTE: During the Asterisk build process, the versions of bison and
flex available on your system are probed. If you have versions of
flex greater than or equal to 2.5.31, it will use flex to build a 
"pure" (re-entrant) tokenizer for expressions. If you use bison version 
greater than 1.85, it will use a bison grammar to generate a pure (re-entrant) 
parser for $[] expressions. 
Notes specific to the flex parser are marked with "**" at the beginning
of the line.

___________________________
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". 

_______________________________
REMOVING CHARACTERS FROM STRING
-------------------------------

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

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

If you want to remove the first N characters from the string assigned
to a variable, simply append a colon and the number of characters to
remove 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 removes everything before 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. 
Note: The arguments and operands of the expression MUST BE separated 
by at least one space. 
** Using the Flex generated tokenizer, this is no longer the case. Spaces
** are only required where they would seperate tokens that would normally
** be merged into a single token. Using the new tokenizer, spaces can be
** used freely.


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".

** Using the new Flex generated tokenizer, the expressions above are still
** legal, but so are the following:
** exten => 1,1,Set(lala=$[1+2])
** exten => 1,2,Set(koko=$[2*    ${lala}])

And, further:

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

will not work as you might have expected. Since all the chars in the single 
token "1+2" are not numbers, it will be evaluated as the string "1+2". Again,
please do not forget, that this is a very simple parsing engine, and it
uses a space (at least one), to separate "tokens".

** Please note that spaces are not required to separate tokens if you have
** Flex version 2.5.31 or higher on your system.
 
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". (only with flex >= 2.5.31)
**          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!
**           (only if flex >= 2.5.31). 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.

The parser must be generated with bison (bison is REQUIRED - yacc cannot 
produce pure parsers, which are reentrant)  The same with flex, if flex
is at 2.5.31 or greater; Re-entrant scanners were not available before that
version.



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:

May  3 15:58:53 WARNING[1234455344]: ast_yyerror(): syntax error: parse error; Input:
 "3072312154"  : "3071234567" & & "Steves Extension" : "Privacy Manager"
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                  ^

The first line shows the string passed to the expression parser. This
string is the result of the variable replacements, etc. This way, you
can see the actual string that went into the parser.

The second line usually shows a string of '^' chars, that show what's
been legally parsed so far.

And the third line shows where the parser was (lookahead token lexing,
etc), when the parse hit the rocks. A single '^' here. The error is
going to be somewhere between the last '^' on the second line, and the
'^' on the third line. That's right, in the example above, there are two
'&' chars, separated by a space, and this is a definite no-no!

** WITH FLEX >= 2.5.31, this has changed slightly. The line showing the 
** part of the expression that was successfully parsed has been dropped,
** and the parse error is explained in a somewhat cryptic format in the log.
** 
** The same line in extensions.conf as above, will now generate an error 
** message in /var/log/asterisk/messages that looks 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).
** 
** As before, 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 a [art 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. flex 2.5.31 or greater should be used. Bison-1.875 or greater. In
**   the case of flex, earlier versions do not generate 'pure', or 
**   reentrant C scanners. In the case of bison-1.875, earlier versions
**   didn't support the location tracking mechanism.

**    http://ftp.gnu.org/gnu/bison/bison-1.875.tar.bz2
**    http://prdownloads.sourceforge.net/lex/flex-2.5.31.tar.bz2?download
**	or http://lex.sourceforge.net/

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

**7.  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.

**8.  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.

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

** THE FOLLOWING UTILITIES ARE PROVIDED ONLY FOR SYSTEMS THAT
** HAVE FLEX-2.5.31 OR GREATER, AND USE THE UPGRADED LEXER!!!
**
** 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)
${BLINDTRANSFER} 	The name of the channel on the other side of a blind transfer
${BRIDGEPEER}	 	Bridged peer
${CALLERANI}	 	* Caller ANI (PRI channels)
${CALLERID}	 	* Caller ID
${CALLERIDNAME}	 	* Caller ID Name only
${CALLERIDNUM}	 	* Caller ID Number only
${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
${DNID}          	* Dialed Number Identifier
${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
${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
${TIMESTAMP}	 	* Current date time in the format: YYYYMMDD-HHMMSS
${TRANSFER_CONTEXT} 	Context for transferred calls
${UNIQUEID}	 	* Current call unique identifier

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 sets 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	

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)
${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
SetVAR(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.