EXTENSION LOGIC : There are two levels of parameter evaluation done in asterisk in extensions.conf. The first, and most frequently used, is the substitution of variable references with their values. Then there are the evaluations done in $[ .. ]. This will be discussed below. ___________________________ 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,SetVar,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 $koko, do: ;exten => 1,2,SetVar,koko=${blabla}${lala} There are also the following special variables: ${ACCOUNTCODE} Account code (if specified) ${CALLERID} Caller ID ${CALLERIDNAME} Caller ID Name only ${CALLERIDNUM} Caller ID Number only ${CHANNEL} Current channel name ${CONTEXT} Current context ${DATETIME} Current date time in the format: YYYY-MM-DD_HH:MM:SS ${DNID} Dialed Number Identifier ${ENUM} Result of application EnumLookup ${EPOCH} Current unix style epoch ${EXTEN} Current extension ${ENV(VAR)} Environmental variable VAR ${HANGUPCAUSE} Asterisk hangup cause ${INVALID_EXTEN}The invalid called extension (used in the "i" extension) ${LANGUAGE} Current language ${LEN(VAR)} String length of VAR (integer) ${MEETMESECS} Number of seconds a user participated in a MeetMe conference ${PRIORITY} Current priority ${RDNIS} Redirected Dial Number ID Service ${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 ${TIMESTAMP} Current date time in the format: YYYYMMDD-HHMMSS ${TXTCIDNAME} Result of application TXTCIDName ${UNIQUEID} Current call unique identifier 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 ${}. For example, SetVar takes as the first argument (before the =) a variable name, so: ;exten => 1,2,SetVar,koko=lala ;exten => 1,3,SetVar,${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". ___________________________ EXPRESSIONS: --------------------------- Everything contained inside a bracket pair prefixed by a $ (like $[this]) is considered as an expression and it is evaluated. Evaluation works similar to (but is done on a later stage than) variable substitution: the expression (including the square brackets) is replaced by the result of the expression evaluation. The arguments and operands of the expression MUST BE separated by at least one space. For example, after the sequence: exten => 1,1,SetVar,"lala=$[1 + 2]"; exten => 1,2,SetVar,"koko=$[2 * ${lala}]"; the value of variable koko is "6". And, further: exten => 1,1,SetVar,"lala=$[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". and, further: exten => 1,1,SetVar,"lala=$[ 1 + 2 ]"; will parse as intended. Extra spaces are ignored. ___________________________ SPACES INSIDE VARIABLE --------------------------- If the variable being evaluated contains spaces, there can be problems. For these cases, double quotes around text that may contain spaces will force the surrounded text to be evaluated as a single token. The double quotes will be counted as part of that lexical token. As an example: exten => s,6,GotoIf($[ "${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. _____________________ 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 : 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. Parentheses are used for grouping in the usual manner. The parser must be parsed with bison (bison is REQUIRED - yacc cannot produce pure parsers, which are reentrant) ___________________________ CONDITIONALS --------------------------- There is one conditional operator - 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,SetVar,"vara=1" exten => s,3,SetVar,"varb=$[${vara} + 2]" exten => s,4,SetVar,"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" & "${CALLERIDNAME}" : "Privacy Manager" ]?callerid-liar|s|1:s|7) You may see an error in /var/log/asterisk/messages like this: May 3 15:58:53 WARNING[1234455344]: ast_yyerror(): syntax error: parse error; Input: "3072312154" : "3071234567" & & "Steves Extension" : "Privacy Manager" ^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^ The first line shows the string passed to the expression parser. This string is the result of the variable replacements, etc. This way, you can see the actual string that went into the parser. The second line usually shows a string of '^' chars, that show what's been legally parsed so far. And the third line shows where the parser was (lookahead token lexing, etc), when the parse hit the rocks. A single '^' here. The error is going to be somewhere between the last '^' on the second line, and the '^' on the third line. That's right, in the example above, there are two '&' chars, separated by a space, and this is a definite no-no! ___________________________ NULL STRINGS --------------------------- Testing to see if a string is null can be done in one of two different ways: exten => _XX.,1,GotoIf($["${calledid}" != ""]?3) exten => _XX.,1,GotoIf($[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.