Asterisk.org: Developer Documentation (28 Oct 2009)

Wed Oct 28 15:49:24 2009

## Asterisk developer's documentation

# Global channel 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.

    ___________________________
    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 : 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 :: 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: 0

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

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

     !( "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.