safely create functions and
      procedures. Since PL functions are executed inside the database
      server, the <literal>TRUSTED</literal> flag should only be given
      for languages that do not allow access to database server
      internals or the file system. The languages
      <application>PL/pgSQL</application>,
      <application>PL/Tcl</application>, and
      <application>PL/Perl</application>
      are considered trusted; the languages
      <application>PL/TclU</application>,
      <application>PL/PerlU</application>, and
      <application>PL/PythonU</application>
      are designed to provide unlimited functionality and should
      <emphasis>not</emphasis> be marked trusted.
     </para>
    </step>
   </procedure>

   <para>
    <xref linkend="xplang-install-example"/> shows how the manual
    installation procedure would work with the language
    <application>PL/Perl</application>.
   </para>

   <example id="xplang-install-example">
    <title>Manual Installation of <application>PL/Perl</application></title>

     <para>
      The following command tells the database server where to find the
      shared object for the <application>PL/Perl</application> language's call
      handler function:

<programlisting>
CREATE FUNCTION plperl_call_handler() RETURNS language_handler AS
    '$libdir/plperl' LANGUAGE C;
</programlisting>
     </para>

     <para>
      <application>PL/Perl</application> has an inline handler function
      and a validator function, so we declare those too:

<programlisting>
CREATE FUNCTION plperl_inline_handler(internal) RETURNS void AS
    '$libdir/plperl' LANGUAGE C STRICT;

CREATE FUNCTION plperl_validator(oid) RETURNS void AS
    '$libdir/plperl' LANGUAGE C STRICT;
</programlisting>
     </para>

     <para>
      The command:
<programlisting>
CREATE TRUSTED LANGUAGE plperl
    HANDLER plperl_call_handler
    INLINE plperl_inline_handler
    VALIDATOR plperl_validator;
</programlisting>
      then defines that the previously declared functions
      should be invoked for functions and procedures where the
      language attribute is <literal>plperl</literal>.
     </para>
  </example>

   <para>
    In a default <productname>PostgreSQL</productname> installation,
    the handler for the <application>PL/pgSQL</application> language
    is built and installed into the <quote>library</quote>
    directory; furthermore, the <application>PL/pgSQL</application> language
    itself is installed in all databases.
    If <application>Tcl</application> support is configured in, the handlers for
    <application>PL/Tcl</application> and <application>PL/TclU</application> are built and installed
    in the library directory, but the language itself is not installed in any
    database by default.
    Likewise, the <application>PL/Perl</application> and <application>PL/PerlU</application>
    handlers are built and installed if Perl support is configured, and the
    <application>PL/PythonU</application> handler is installed if Python support is
    configured, but these languages are not installed by default.
   </para>

  </sect1>

</chapter>