The Asterisk Extension Language - v 2 ===================================== AEL is a specialized language intended purely for describing Asterisk dial plans. The current version was written by Steve Murphy, and is a rewrite of the original version. This new version further extends AEL, and provides more flexible syntax, better error messages, and some missing functionality. AEL is really the merger of 4 different 'languages', or syntaxes: * The first and most obvious is the AEL syntax itself. A BNF is provided near the end of this document. * The second syntax is the Expression Syntax, which is normally handled by Asterisk extension engine, as expressions enclosed in $[...]. The right hand side of assignments are wrapped in $[ ... ] by AEL, and so are the if and while expressions, among others. * The third syntax is the Variable Reference Syntax, the stuff enclosed in ${..} curly braces. It's a bit more involved than just putting a variable name in there. You can include one of dozens of 'functions', and their arguments, and there are even some string manipulation notation in there. * The last syntax that underlies AEL, and is not used directly in AEL, is the Extension Language Syntax. The extension language is what you see in extensions.conf, and AEL compiles the higher level AEL language into extensions and priorities, and passes them via function calls into Asterisk. Embedded in this language is the Application/AGI commands, of which one application call per step, or priority can be made. You can think of this as a "macro assembler" language, that AEL will compile into. Any programmer of AEL should be familiar with it's syntax, of course, as well as the Expression syntax, and the Variable syntax. ************************** * Asterisk in a Nutshell * ************************** Asterisk acts as a server. Devices involved in telephony, like Zapata cards, or Voip phones, all indicate some context that should be activated in their behalf. See the config file formats for IAX, SIP, zapata.conf, etc. They all help describe a device, and they all specify a context to activate when somebody picks up a phone, or a call comes in from the phone company, or a voip phone, etc. Contexts -------- Contexts are a grouping of extensions. Contexts can also include other contexts. Think of it as a sort of merge operation at runtime, whereby the included context's extensions are added to the contexts making the inclusion. Extensions and priorities ------------------------- A Context contains zero or more Extensions. There are several predefined extensions. The "s" extension is the "start" extension, and when a device activates a context the "s" extension is the one that is going to be run. Other extensions are the timeout "t" extension, the invalid response, or "i" extension, and there's a "fax" extension. For instance, a normal call will activate the "s" extension, but an incoming FAX call will come into the "fax" extension, if it exists. (BTW, asterisk can tell it's a fax call by the little "beep" that the calling fax machine emits every so many seconds.). Extensions contain several priorities, which are individual instructions to perform. Some are as simple as setting a variable to a value. Others are as complex as initiating the Voicemail application, for instance. Priorities are executed in order. When the 's" extension completes, asterisk waits until the timeout for a response. If the response matches an extension's pattern in the context, then control is transferred to that extension. Usually the responses are tones emitted when a user presses a button on their phone. For instance, a context associated with a desk phone might not have any "s" extension. It just plays a dialtone until someone starts hitting numbers on the keypad, gather the number, find a matching extension, and begin executing it. That extension might Dial out over a connected telephone line for the user, and then connect the two lines together. The extensions can also contain "goto" or "jump" commands to skip to extensions in other contexts. Conditionals provide the ability to react to different stimuli, and there you have it. Macros ------ Think of a macro as a combination of a context with one nameless extension, and a subroutine. It has arguments like a subroutine might. A macro call can be made within an extension, and the individual statements there are executed until it ends. At this point, execution returns to the next statement after the macro call. Macros can call other macros. And they work just like function calls. Applications ------------ Application calls, like "Dial()", or "Hangup()", or "Answer()", are available for users to use to accomplish the work of the dialplan. There are over 145 of them at the moment this was written, and the list grows as new needs and wants are uncovered. Some applications do fairly simple things, some provide amazingly complex services. Hopefully, the above objects will allow you do anything you need to in the Asterisk environment! ******************* * Getting Started * ******************* The AEL parser (pbx_ael.so) is completely separate from the module that parses extensions.conf (pbx_config.so). To use AEL, the only thing that has to be done is the module pbx_ael.so must be loaded by Asterisk. This will be done automatically if using 'autoload=yes' in /etc/asterisk/modules.conf. When the module is loaded, it will look for 'extensions.ael' in /etc/asterisk/. extensions.conf and extensions.ael can be used in conjunction with each other if that is what is desired. Some users may want to keep extensions.conf for the features that are configured in the 'general' section of extensions.conf. ------------------------------ - Reloading extensions.ael - ------------------------------ To reload extensions.ael, the following command can be issued at the CLI: *CLI> ael reload ************* * Debugging * ************* Right at this moment, the following commands are available, but do nothing: Enable AEL contexts debug *CLI> ael debug contexts Enable AEL macros debug *CLI> ael debug macros Enable AEL read debug *CLI> ael debug read Enable AEL tokens debug *CLI> ael debug tokens Disable AEL debug messages *CLI> ael no debug If things are going wrong in your dialplan, you can use the following facilities to debug your file: 1. The messages log in /var/log/asterisk. (from the checks done at load time). 2. the "show dialplan" command in asterisk 3. the standalone executable, "aelparse" built in the utils/ dir in the source. ***************************** * About "aelparse" * ***************************** You can use the "aelparse" program to check your extensions.ael file before feeding it to asterisk. Wouldn't it be nice to eliminate most errors before giving the file to asterisk? aelparse is compiled in the utils directory of the asterisk release. It isn't installed anywhere (yet). You can copy it to your favorite spot in your PATH. aelparse has two optional arguments: -d - Override the normal location of the config file dir, (usually /etc/asterisk), and use the current directory instead as the config file dir. Aelparse will then expect to find the file "./extensions.ael" in the current directory, and any included files in the current directory as well. -n - don't show all the function calls to set priorities and contexts within asterisk. It will just show the errors and warnings from the parsing and semantic checking phases. ****************************** * General Notes about Syntax * ****************************** Note that the syntax and style are now a little more free-form. The opening '{' (curly-braces) do not have to be on the same line as the keyword that precedes them. Statements can be split across lines, as long as tokens are not broken by doing so. More than one statement can be included on a single line. Whatever you think is best! You can just as easily say, if(${x}=1) { NoOp(hello!); goto s|3; } else { NoOp(Goodbye!); goto s|12; } as you can say: if(${x}=1) { NoOp(hello!); goto s|3; } else { NoOp(Goodbye!); goto s|12; } or: if(${x}=1) { NoOp(hello!); goto s|3; } else { NoOp(Goodbye!); goto s|12; } or: if (${x}=1) { NoOp(hello!); goto s|3; } else { NoOp(Goodbye!); goto s|12; } or even: if (${x}=1) { NoOp(hello!); goto s|3; } else { NoOp(Goodbye!); goto s|12; } ************ * Keywords * ************ The AEL keywords are case-sensitive. If an application name and a keyword overlap, there is probably good reason, and you should consider replacing the application call with an AEL statement. If you do not wish to do so, you can still use the application, by using a capitalized letter somewhere in its name. In the Asterisk extension language, application names are NOT case-sensitive. The following are keywords in the AEL language: * abstract * context * macro * globals * ignorepat * switch * if * ifTime * else * random * goto * jump * return * break * continue * regexten * hint * for * while * case * pattern * default NOTE: the "default" keyword can be used as a context name, for those who would like to do so. * catch * switches * eswitches * includes Procedural Interface and Internals ================================== AEL first parses the extensions.ael file into a memory structure representing the file. The entire file is represented by a tree of "pval" structures linked together. This tree is then handed to the semantic check routine. Then the tree is handed to the compiler. After that, it is freed from memory. A program could be written that could build a tree of pval structures, and a pretty printing function is provided, that would dump the data to a file, or the tree could be handed to the compiler to merge the data into the asterisk dialplan. The modularity of the design offers several opportunities for developers to simplify apps to generate dialplan data. ========================= AEL version 2 BNF ========================= (hopefully, something close to bnf). First, some basic objects ------------------------ a lexical token consisting of characters matching this pattern: [-a-zA-Z0-9"_/.\<\>\*\+!$#\[\]][-a-zA-Z0-9"_/.!\*\+\<\>\{\}$#\[\]]* a concatenation of up to 3 s. all characters encountered until the character that follows the in the grammar. ------------------------- :== :== | :== | | | ';' :== 'context' '{' '}' | 'context' '{' '}' | 'context' 'default' '{' '}' | 'context' 'default' '{' '}' | 'abstract' 'context' '{' '}' | 'abstract' 'context' '{' '}' | 'abstract' 'context' 'default' '{' '}' | 'abstract' 'context' 'default' '{' '}' :== 'macro' '(' ')' '{' '}' | 'macro' '(' ')' '{' '}' | 'macro' '(' ')' '{' '}' | 'macro' '(' ')' '{' '}' :== 'globals' '{' '}' | 'globals' '{' '}' :== | :== '=' ';' :== | ',' :== | :== | | | | | '=' ';' | ';' :== 'ignorepat' '=>' ';' :== '=>' | 'regexten' '=>' | 'hint' '(' ')' '=>' | 'regexten' 'hint' '(' ')' '=>' :== | :== 'if' '(' ')' :== 'random' '(' ')' :== 'ifTime' '(' ':' ':' '|' '|' '|' ')' | 'ifTime' '(' '|' '|' '|' ')' :== | | :== 'switch' '(' ')' '{' :== '{' '}' | '=' ';' | 'goto' ';' | 'jump' ';' | ':' | 'for' '(' ';' ';' ')' | 'while' '(' ')' | '}' | '}' | '&' macro_call ';' | ';' | '=' ';' | 'break' ';' | 'return' ';' | 'continue' ';' | | 'else' | | 'else' | | 'else' | ';' :== | '|' | '|' '|' | 'default' '|' '|' | ',' | ',' ',' | 'default' ',' ',' :== | ',' | ',' '@' | '@' | ',' '@' 'default' | '@' 'default' :== '(' ')' | '(' ')' :== '(' :== ')' | ')' :== | ',' | /* nothing */ | ',' /* nothing */ :== | :== 'case' ':' | 'default' ':' | 'pattern' ':' | 'case' ':' | 'default' ':' | 'pattern' ':' :== | :== | 'catch' '{' '}' :== 'switches' '{' '}' | 'switches' '{' '}' :== 'eswitches' '{' '}' | 'eswitches' '{' '}' :== ';' | ';' :== ';' | '|' ':' ':' '|' '|' '|' ';' | '|' '|' '|' '|' ';' | ';' | '|' ':' ':' '|' '|' '|' ';' | '|' '|' '|' '|' ';' :== | 'default' :== 'includes' '{' '}' | 'includes' '{' '}' ************************** * AEL Example USAGE ***** ************************** Comments ======== Comments begin with // and end with the end of the line. Comments are removed by the lexical scanner, and will not be recognized in places where it is busy gathering expressions to wrap in $[] , or inside application call argument lists. The safest place to put comments is after terminating semicolons, or on otherwise empty lines. Context ======= Contexts in AEL represent a set of extensions in the same way that they do in extensions.conf. context default { } A context can be declared to be "abstract", in which case, this declaration expresses the intent of the writer, that this context will only be included by another context, and not "stand on its own". The current effect of this keyword is to prevent "goto " statements from being checked. abstract context longdist { _1NXXNXXXXXX => NoOp(generic long distance dialing actions in the US); } Extensions ========== To specify an extension in a context, the following syntax is used. If more than one application is be called in an extension, they can be listed in order inside of a block. context default { 1234 => Playback(tt-monkeys); 8000 => { NoOp(one); NoOp(two); NoOp(three); }; _5XXX => NoOp(it's a pattern!); } Two optional items have been added to the AEL syntax, that allow the specification of hints, and a keyword, regexten, that will force the numbering of priorities to start at 2. The ability to make extensions match by CID is preserved in AEL; just use '/' and the CID number in the specification. See below. context default { regexten _5XXX => NoOp(it's a pattern!); } context default { hint(Sip/1) _5XXX => NoOp(it's a pattern!); } context default { regexten hint(Sip/1) _5XXX => NoOp(it's a pattern!); } The regexten must come before the hint if they are both present. CID matching is done as with the extensions.conf file. Follow the extension name/number with a slash (/) and the number to match against the Caller ID: context zoombo { 819/7079953345 => { NoOp(hello, 3345); } } In the above, the 819/7079953345 extension will only be matched if the CallerID is 7079953345, and the dialed number is 819. Hopefully you have another 819 extension defined for all those who wish 819, that are not so lucky as to have 7079953345 as their CallerID! Includes ======== Contexts can be included in other contexts. All included contexts are listed within a single block. context default { includes { local; longdistance; international; } } Time-limited inclusions can be specified, as in extensions.conf format, with the fields described in the wiki page Asterisk cmd GotoIfTime. context default { includes { local; longdistance|16:00-23:59|mon-fri|*|*; international; } } #include ======== You can include other files with the #include "filepath" construct. #include "/etc/asterisk/testfor.ael" An interesting property of the #include, is that you can use it almost anywhere in the .ael file. It is possible to include the contents of a file in a macro, context, or even extension. The #include does not have to occur at the beginning of a line. Included files can include other files, up to 50 levels deep. If the path provided in quotes is a relative path, the parser looks in the config file directory for the file (usually /etc/asterisk). Dialplan Switches ================= Switches are listed in their own block within a context. For clues as to what these are used for, see Asterisk - dual servers, and Asterisk config extensions.conf. context default { switches { DUNDi/e164; IAX2/box5; }; eswitches { IAX2/context@${CURSERVER}; } } Ignorepat ========= ignorepat can be used to instruct channel drivers to not cancel dialtone upon receipt of a particular pattern. The most commonly used example is '9'. context outgoing { ignorepat => 9; } Variables ========= Variables in Asterisk do not have a type, so to define a variable, it just has to be specified with a value. Global variables are set in their own block. globals { CONSOLE=Console/dsp; TRUNK=Zap/g2; } Variables can be set within extensions as well. context foo { 555 => { x=5; y=blah; divexample=10/2 NoOp(x is ${x} and y is ${y} !); } } NOTE: AEL wraps the right hand side of an assignment with $[ ] to allow expressions to be used If this is unwanted, you can protect the right hand side from being wrapped by using the Set() application. Read the README.variables about the requirements and behavior of $[ ] expressions. NOTE: These things are wrapped up in a $[ ] expression: The while() test; the if() test; the middle expression in the for( x; y; z) statement (the y expression); Assignments - the right hand side, so a = b -> Set(a=$[b]) Writing to a dialplan function is treated the same as writing to a variable. context blah { s => { CALLERID(name)=ChickenMan; NoOp(My name is ${CALLERID(name)} !); } } Loops ===== AEL has implementations of 'for' and 'while' loops. context loops { 1 => { for (x=0; ${x} < 3; x=${x} + 1) { Verbose(x is ${x} !); } } 2 => { y=10; while (${y} >= 0) { Verbose(y is ${y} !); y=${y}-1; } } } NOTE: The conditional expression (the "${y} >= 0" above) is wrapped in $[ ] so it can be evaluated. NOTE: The for loop test expression (the "${x} < 3" above) is wrapped in $[ ] so it can be evaluated. Conditionals ============ AEL supports if and switch statements, like AEL, but adds ifTime, and random. Unlike the original AEL, though, you do NOT need to put curly braces around a single statement in the "true" branch of an if(), the random(), or an ifTime() statement. The if(), ifTime(), and random() statements allow optional else clause. context conditional { _8XXX => { Dial(SIP/${EXTEN}); if ("${DIALSTATUS}" = "BUSY") { NoOp(yessir); Voicemail(${EXTEN}|b); } else Voicemail(${EXTEN}|u); ifTime (14:00-25:00|sat-sun|*|*) Voicemail(${EXTEN}|b); else { Voicemail(${EXTEN}|u); NoOp(hi, there!); } random(51) NoOp(This should appear 51% of the time); random( 60 ) { NoOp( This should appear 60% of the time ); } else { random(75) { NoOp( This should appear 30% of the time! ); } else { NoOp( This should appear 10% of the time! ); } } } _777X => { switch (${EXTEN}) { case 7771: NoOp(You called 7771!); break; case 7772: NoOp(You called 7772!); break; case 7773: NoOp(You called 7773!); // fall thru- pattern 777[4-9]: NoOp(You called 777 something!); default: NoOp(In the default clause!); } } } NOTE: The conditional expression in if() statements (the "${DIALSTATUS}" = "BUSY" above) is wrapped by the compiler in $[] for evaluation. NOTE: Neither the switch nor case values are wrapped in $[ ]; they can be constants, or ${var} type references only. NOTE: AEL generates each case as a separate extension. case clauses with no terminating 'break', or 'goto', have a goto inserted, to the next clause, which creates a 'fall thru' effect. NOTE: AEL introduces the ifTime keyword/statement, which works just like the if() statement, but the expression is a time value, exactly like that used by the application GotoIfTime(). See Asterisk cmd GotoIfTime NOTE: The pattern statement makes sure the new extension that is created has an '_' preceding it to make sure asterisk recognizes the extension name as a pattern. NOTE: Every character enclosed by the switch expression's parenthesis are included verbatim in the labels generated. So watch out for spaces! NOTE: NEW: Previous to version 0.13, the random statement used the "Random()" application, which has been deprecated. It now uses the RAND() function instead, in the GotoIf application. Break, Continue, and Return =========================== Three keywords, break, continue, and return, are included in the syntax to provide flow of control to loops, and switches. The break can be used in switches and loops, to jump to the end of the loop or switch. The continue can be used in loops (while and for) to immediately jump to the end of the loop. In the case of a for loop, the increment and test will then be performed. In the case of the while loop, the continue will jump to the test at the top of the loop. The return keyword will cause an immediate jump to the end of the context, or macro, and can be used anywhere. goto, jump, and labels ====================== This is an example of how to do a goto in AEL. context gotoexample { s => { begin: NoOp(Infinite Loop! yay!); Wait(1); goto begin; // go to label in same extension } 3 => { goto s|begin; // go to label in different extension } 4 => { goto gotoexample|s|begin; // overkill go to label in same context } } context gotoexample2 { s => { end: goto gotoexample|s|begin; // go to label in different context } } You can use the special label of "1" in the goto and jump statements. It means the "first" statement in the extension. I would not advise trying to use numeric labels other than "1" in goto's or jumps, nor would I advise declaring a "1" label anywhere! As a matter of fact, it would be bad form to declare a numeric label, and it might conflict with the priority numbers used internally by asterisk. The syntax of the jump statement is: jump extension[,priority][@context] If priority is absent, it defaults to "1". If context is not present, it is assumed to be the same as that which contains the "jump". context gotoexample { s => { begin: NoOp(Infinite Loop! yay!); Wait(1); jump s; // go to first extension in same extension } 3 => { jump s,begin; // go to label in different extension } 4 => { jump s,begin@gotoexample; // overkill go to label in same context } } context gotoexample2 { s => { end: jump s@gotoexample; // go to label in different context } } NOTE: goto labels follow the same requirements as the Goto() application, except the last value has to be a label. If the label does not exist, you will have run-time errors. If the label exists, but in a different extension, you have to specify both the extension name and label in the goto, as in: goto s|z; if the label is in a different context, you specify context|extension|label. There is a note about using goto's in a switch statement below... NOTE AEL introduces the special label "1", which is the beginning context number for most extensions. NOTE: A NEW addition to AEL: you can now use ',' instead of '|' to separate the items in the target address. You can't have a mix, though, of '|' and ',' in the target. It's either one, or the other. Macros ====== A macro is defined in its own block like this. The arguments to the macro are specified with the name of the macro. They are then referred to by that same name. A catch block can be specified to catch special extensions. macro std-exten( ext , dev ) { Dial(${dev}/${ext},20); switch(${DIALSTATUS) { case BUSY: Voicemail(b${ext}); break; default: Voicemail(u${ext}); } catch a { VoiceMailMain(${ext}); return; } } A macro is then called by preceding the macro name with an ampersand. Empty arguments can be passed simply with nothing between comments(0.11). context example { _5XXX => &std-exten(${EXTEN}, "IAX2"); _6XXX => &std-exten(, "IAX2"); _7XXX => &std-exten(${EXTEN},); _8XXX => &std-exten(,); } Examples ======== context demo { s => { Wait(1); Answer(); TIMEOUT(digit)=5; TIMEOUT(response)=10; restart: Background(demo-congrats); instructions: for (x=0; ${x} < 3; x=${x} + 1) { Background(demo-instruct); WaitExten(); } } 2 => { Background(demo-moreinfo); goto s|instructions; } 3 => { LANGUAGE()=fr; goto s|restart; } 500 => { Playback(demo-abouttotry); Dial(IAX2/guest@misery.digium.com); Playback(demo-nogo); goto s|instructions; } 600 => { Playback(demo-echotest); Echo(); Playback(demo-echodone); goto s|instructions; } # => { hangup: Playback(demo-thanks); Hangup(); } t => goto #|hangup; i => Playback(invalid); } Semantic Checks =============== AEL, after parsing, but before compiling, traverses the dialplan tree, and makes several checks: * Macro calls to non-existent macros. * Macro calls to contexts. * Macro calls with argument count not matching the definition. * application call to macro. (missing the '&') * application calls to "GotoIf", "GotoIfTime", "while", "endwhile", "Random", and "execIf", will generate a message to consider converting the call to AEL goto, while, etc. constructs. * goto a label in an empty extension. * goto a non-existent label, either a within-extension, within-context, or in a different context, or in any included contexts. Will even check "sister" context references. * All the checks done on the time values in the dial plan, are done on the time values in the ifTime() and includes times: o the time range has to have two times separated by a dash; o the times have to be in range of 0 to 24 hours. o The weekdays have to match the internal list, if they are provided; o the day of the month, if provided, must be in range of 1 to 31; o the month name or names have to match those in the internal list. * (0.5) If an expression is wrapped in $[ ... ], and the compiler will wrap it again, a warning is issued. * (0.5) If an expression had operators (you know, +,-,*,/,%,!,etc), but no ${ } variables, a warning is issued. Maybe someone forgot to wrap a variable name? * (0.12) check for duplicate context names. * (0.12) check for abstract contexts that are not included by any context. * (0.13) Issue a warning if a label is a numeric value. There are a subset of checks that have been removed until the proposed AAL (Asterisk Argument Language) is developed and incorporated into Asterisk. These checks will be: * (if the application argument analyzer is working: the presence of the 'j' option is reported as error. * if options are specified, that are not available in an application. * if you specify too many arguments to an application. * a required argument is not present in an application call. * Switch-case using "known" variables that applications set, that does not cover all the possible values. (a "default" case will solve this problem. Each "unhandled" value is listed. * a Switch construct is used, which is uses a known variable, and the application that would set that variable is not called in the same extension. This is a warning only... * Calls to applications not in the "applist" database (installed in /var/lib/asterisk/applist" on most systems). * In an assignment statement, if the assignment is to a function, the function name used is checked to see if it one of the currently known functions. A warning is issued if it is not. Differences with the original version of AEL ============================================ 1. The $[...] expressions have been enhanced to include the ==, ||, and && operators. These operators are exactly equivalent to the =, |, and & operators, respectively. Why? So the C, Java, C++ hackers feel at home here. 2. It is more free-form. The newline character means very little, and is pulled out of the white-space only for line numbers in error messages. 3. It generates more error messages -- by this I mean that any difference between the input and the grammar are reported, by file, line number, and column. 4. It checks the contents of $[ ] expressions (or what will end up being $[ ] expressions!) for syntax errors. It also does matching paren/bracket counts. 5. It runs several semantic checks after the parsing is over, but before the compiling begins, see the list above. 6. It handles #include "filepath" directives. -- ALMOST anywhere, in fact. You could easily include a file in a context, in an extension, or at the root level. Files can be included in files that are included in files, down to 50 levels of hierarchy... 7. Local Goto's inside Switch statements automatically have the extension of the location of the switch statement appended to them. 8. A pretty printer function is available within pbx_ael.so. 9. In the utils directory, two standalone programs are supplied for debugging AEL files. One is called "aelparse", and it reads in the /etc/asterisk/extensions.ael file, and shows the results of syntax and semantic checking on stdout, and also shows the results of compilation to stdout. The other is "aelparse1", which uses the original ael compiler to do the same work, reading in "/etc/asterisk/extensions.ael", using the original 'pbx_ael.so' instead. 10. AEL supports the "jump" statement, and the "pattern" statement in switch constructs. Hopefully these will be documented in the AEL README. 11. Added the "return" keyword, which will jump to the end of an extension/Macro. 12. Added the ifTime (