intended
    for extensions that include C code, although it can be used for
    pure-SQL extensions too.  Note that <acronym>PGXS</acronym> is not
    intended to be a universal build system framework that can be used
    to build any software interfacing to <productname>PostgreSQL</productname>;
    it simply automates common build rules for simple server extension
    modules.  For more complicated packages, you might need to write your
    own build system.
   </para>

   <para>
    To use the <acronym>PGXS</acronym> infrastructure for your extension,
    you must write a simple makefile.
    In the makefile, you need to set some variables
    and include the global <acronym>PGXS</acronym> makefile.
    Here is an example that builds an extension module named
    <literal>isbn_issn</literal>, consisting of a shared library containing
    some C code, an extension control file, an SQL script, an include file
    (only needed if other modules might need to access the extension functions
    without going via SQL), and a documentation text file:
<programlisting>
MODULES = isbn_issn
EXTENSION = isbn_issn
DATA = isbn_issn--1.0.sql
DOCS = README.isbn_issn
HEADERS_isbn_issn = isbn_issn.h

PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
</programlisting>
    The last three lines should always be the same.  Earlier in the
    file, you assign variables or add custom
    <application>make</application> rules.
   </para>

   <para>
    Set one of these three variables to specify what is built:

    <variablelist>
     <varlistentry id="extend-pgxs-modules">
      <term><varname>MODULES</varname></term>
      <listitem>
       <para>
        list of shared-library objects to be built from source files with same
        stem (do not include library suffixes in this list)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="extend-pgxs-module-big">
      <term><varname>MODULE_big</varname></term>
      <listitem>
       <para>
        a shared library to build from multiple source files
        (list object files in <varname>OBJS</varname>)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="extend-pgxs-program">
      <term><varname>PROGRAM</varname></term>
      <listitem>
       <para>
        an executable program to build
        (list object files in <varname>OBJS</varname>)
       </para>
      </listitem>
     </varlistentry>
    </variablelist>

    The following variables can also be set:

    <variablelist>
     <varlistentry id="extend-pgxs-extension">
      <term><varname>EXTENSION</varname></term>
      <listitem>
       <para>
        extension name(s); for each name you must provide an
        <literal><replaceable>extension</replaceable>.control</literal> file,
        which will be installed into
        <literal><replaceable>prefix</replaceable>/share/extension</literal>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="extend-pgxs-moduledir">
      <term><varname>MODULEDIR</varname></term>
      <listitem>
       <para>
        subdirectory of <literal><replaceable>prefix</replaceable>/share</literal>
        into which DATA and DOCS files should be installed
        (if not set, default is <literal>extension</literal> if
        <varname>EXTENSION</varname> is set,
        or <literal>contrib</literal> if not)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="extend-pgxs-data">
      <term><varname>DATA</varname></term>
      <listitem>
       <para>
        random files to install into <literal><replaceable>prefix</replaceable>/share/$MODULEDIR</literal>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="extend-pgxs-data-built">
      <term><varname>DATA_built</varname></term>
      <listitem>
       <para>
        random files to install into
        <literal><replaceable>prefix</replaceable>/share/$MODULEDIR</literal>,
        which need to be built first