kamailio/doc/tutorials/select_list/docbook/intro.xml

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<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<chapter id="Select_Intro">
	<title>Introduction and Notations</title>
	<section id="Intro">
	<title>Introduction</title>
	<para>Selects are read-only functions that can be used in the script and
	that always return a string value. In the script a select always starts
	with a &apos;<emphasis>@</emphasis>&apos;. In an expression context a
	select always evaluates to either a string or undef.
	</para>
	<para>For more informations see
		<ulink url=' http://sip-router.org/wiki/cookbooks/selects/devel'>
			http://sip-router.org/wiki/cookbooks/selects/devel</ulink>.
	</para>
	<para>This document lists all the selects implemented by each module.
	</para>
	</section>
	<section id="Notations">
	<title>Notations</title>
	<para>The following notations are used:
	<orderedlist>
	<listitem><para>@  - all selects always start with '@'.</para></listitem>
	<listitem><para>&quot;string&quot; - string type.</para></listitem>
	<listitem><para>integer - integer type.</para></listitem>
	<listitem><para>[] - Parameter markers. Can be either [integer] or
		[&quot;string&quot;].
		Note that instead of [&quot;string&quot;] one could write .string,
		e.g.:
		@foo.bar[&quot;string&quot;] is equivalent to @foo.bar.string.
	</para></listitem>
	<listitem><para>{} - denotes an optional parameter.
		E.g.: @ruri.params{[&quot;string&quot;]} means you could use
		@ruri.params by itself or you could specify an extra parameter:
		@ruri.params[&quot;trasnport&quot;] or @ruri.params.transport.
	</para></listitem>
	<listitem><para>&lt;string&gt; - means the next member is not fixed and can
		take any string value (it is a string parameter).
		It is equivalent with [&quot;string&quot;], e.g.:
		@msg.header.&lt;string&gt; is the same as
		@msg.header[&quot;string&quot;].
		It is used only to expose an internal implementation detail
		(SEL_PARAM_* vs. CONSUME_NEXT_*), but from the script writer point
		of view it is the same thing.
	</para></listitem>
	<listitem><para>.* - means the select can be followed by a variable number
		of string parameters.
		E.g.: @cfg_get.*  means that @cfg_get.core.version is a valid usage.
	</para></listitem>
	<listitem><para>* (without a &apos;.&apos; in front) - it means the
		last member might be a class that might expand further (but the
		&quot;expansion&quot; is not defined in the same module).
		E.g. @foo.nameaddr* means that nameaddr is most likely
		a class that expands further
		(for example into @foo.nameaddr.uri a.s.o).
	</para></listitem>
	</orderedlist>
	</para>
	</section>
</chapter>