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Q: What is a callback (command) ?

A: A callback is a command or set of commands that is called by KVIrc in
   response to an event. It is similar to an event handler; the difference
   is that the event handler is usually static, the callback is "created"
   at runtime instead.
   Consider the command exec (see /help exec); its syntax is as follows:

   exec(<commandline>[,<magicparams>])
   {
     <callback>
   }

   The <callback> is a list of commands that will be called by KVIrc when
   the <commandline> has been executed and the slave process has printed
   some data on its stdout.


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Q: How can i print on a window the result of an external command like nmap
   or uname ?

A: Starting from version 3.0.0 KVIrc supports (again) the /exec command.
   The commandline you're looking for might be something similar to:

     exec("uname -a"){ echo $1; };

   If you want to say the result to a channel you may use say instead of echo

     exec("uname -a"){ say $1; };

   For nmap you might consider using the -e switch too in order to see
   the errors printed on stderr.

     exec -e ("nmap -sS -p 1-1024 somehost"){ say $1; }

   Exec is a really flexible command, it can process the slave output in blocks
   or as a whole and can write data to the slave too. See /help exec for
   more details.

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Q: KVIrc crashes when I use a commandline like the following:
   alias(identify){ identify password; }

A: This is infinite recursion: a programming error.
   Take a look at http://en.wikipedia.org/wiki/Infinite_loop , learn
   that once for all and fix your script.