![]() |
![]() |
Using perl from KVS and vice-versa.How to use perl from KVS and KVS from perl. |
|||||
Introduction | |||||
Starting from version 3.0.2 you can include perl code snippets in KVS code and you can use KVS commands from within perl. This feature is present only if a working perl installation has been found at build time. | |||||
Using perl from KVS | |||||
Using perl from KVIrc is really easy: just enclose your perl code snippet inside perl.begin and perl.end.
If you have already encountered the KVIrc's eval command that you probably also know how to execute a perl code snippet from a file :) | |||||
Using KVS from perl | |||||
KVIrc exports several commands to the perl namespace that allow you to invoke KVIrc's functions from inside the perl code snippet. The nicest example is KVIrc::echo():
KVIrc::echo(<text>[,<colorset>[,<windowid>]]) <text> is obviously the text to be printed. <colorset> is the equivalent of the echo -i option and <windowid> is the equivalent of the -w option. Both <colorset> and <windowid> can be omitted (in this case KVIrc will use a default colorset and the current window). | |||||
Perl execution contexts | |||||
The perl code snippets are executed by the means of a perl interpreter. Each perl interpreter has its own context and thus it's own variables, own function namespace etc. In the example above KVIrc creates an interpreter when perl.begin is invoked and destroys it at perl.end parsing time. In fact, KVIrc can mantain multiple persistent interpreters that will allow you to preserve your context across perl.begin invocations. You can invoke a specific perl context by passing it as parameter to the perl.begin command.
In fact there is a third possibility to destroy a context: it's when the perlcore module is forcibly unloaded (by the means of /perlcore.unload) but this is really a rare case and should be threated just like a KVIrc restart (the user probably WANTS the contexts to be reinitialized). The nice thing is that not only your variables will get preserved but also any perl function or class you declare in a context will persist. It's just like executing a long perl script file with pauses inside. If you omit the perl context name in the perl.begin command (or if you use an empty string in it's place) then KVIrc will create a temporary context for the snippet execution and will destroy it immediately after perl.end has been called. The major side effect of keeping persistent perl contexts is that the perl's symbol table will grow and if not used carefully the interpreter may become a memory hog. So if you're going to use persistent contexts either try to keep the symbol table clean or explicitly call perl.destroy once in a while to recreate the interpreter. If you just execute occasional perl code snippets and don't need to keep persistent variables then just use the nameless temporary context provided by perl.begin(""). | |||||
Passing parameters to the perl script | |||||
The easiest way to pass parameters to the perl code snippet is to put them as perl.begin arguments. In fact the complete syntax of perl.begin is: perl.begin(<perl context>,<arg0>,<arg1>,...) Where the <arg0>,<arg1>...<argN> parameters are passed to the perl context as elements of the $_[] array.
| |||||
Accessing the KVIrc scripting context from perl | |||||
KVIrc exposes the following functions that manipulate the variables of the KVIrc's current KVS execution context. KVIrc::getLocal(<x>) Returns the value of the KVIrc's local variable %x. KVIrc::getGlobal(<Y>) Returns the value of the KVIrc's global variable %Y. KVIrc::setLocal(<x>,<value>) Sets the KVIrc's global variable %x to <value> KVIrc::setGlobal(<Y>,<value>) Sets the KVIrc's global variable %Y to <value> The local variables interested belong to the current KVS exection context while the global variables are visible everywhere.
| |||||
Executing arbitrary KVIrc commands from perl | |||||
You can execute arbitrary KVS commands from perl by the means of: KVIrc::eval(<code>) This function behaves exactly like the ${ <code> } KVS construct: it executes <code> in a child context and returns it's evaluation retult. The following two code snippets have equivalent visible effects:
Remember that the perl code snippet is evaluated in a child KVS context and thus the local variables are NOT visible!. The following code snippets may easily fool you:
Note also that you must either escape the $ at the beginning of the KVIrc identifiers or use the single quotes to prevent perl from catching the $ as the beginning of a variable.
| |||||
A shortcut for KVIrc::eval("/say...") | |||||
Since KVIrc::eval("/say...") is a common calling pattern then say has been added to the KVIrc perl namespace. You can now call
KVIrc::say(<text>[,<windowid>]) and the semantics are obvious (see also /say). | |||||
The perl script return values | |||||
The perl.begin command propagates the perl code return value to the KVIrc context (just like a setreturn() would do). In fact the perl snippet return value is the last "thing" that the interpreter evaluates. In this way you can write perl aliases that return values without doing any variable passing equilibrism. | |||||
Executing perl scripts from files | |||||
| |||||
Other tricks | |||||
An interesting feature of the persistent perl contexts is that you can prepare a context for a later fast execution. The idea is to declare perl functions in a single perl code snippet and to call the single functions when a fast execution is needed. For example you might parse the following snippet at KVIrc's startup:
| |||||
Curiosity | |||||
The perl support in KVIrc is implemented as a master-slave module pair. The perl.* module is the master while perlcore is the slave. When the perl support isn't compiled in, the perl.* commands print some warnings and exit gracefully while the perlcore module refuses to be loaded. When perl support is compiled in but for some reason the libperl.so can't be found or loaded then perlcore fails the dynamic loading stage but perl.* still fails gracefully with just some warning messages. This trick allows the scripters to check for perl support with $perl.isavailable and to embed perl code snippets in KVS even if the support is missing. The snippets will be just skipped. Happy perl hacking :) |