<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Modules and the unknown command</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="PL/Tcl - Tcl Procedural Language" HREF="pltcl.html"><LINK REL="PREVIOUS" TITLE="Trigger Procedures in PL/Tcl" HREF="pltcl-trigger.html"><LINK REL="NEXT" TITLE="Tcl Procedure Names" HREF="pltcl-procnames.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="pltcl-trigger.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="pltcl.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 36. PL/Tcl - Tcl Procedural Language</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="pltcl.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="pltcl-procnames.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="PLTCL-UNKNOWN" >36.7. Modules and the <CODE CLASS="FUNCTION" >unknown</CODE > command</A ></H1 ><P > PL/Tcl has support for autoloading Tcl code when used. It recognizes a special table, <TT CLASS="LITERAL" >pltcl_modules</TT >, which is presumed to contain modules of Tcl code. If this table exists, the module <TT CLASS="LITERAL" >unknown</TT > is fetched from the table and loaded into the Tcl interpreter immediately after creating the interpreter. </P ><P > While the <TT CLASS="LITERAL" >unknown</TT > module could actually contain any initialization script you need, it normally defines a Tcl <CODE CLASS="FUNCTION" >unknown</CODE > procedure that is invoked whenever Tcl does not recognize an invoked procedure name. <SPAN CLASS="APPLICATION" >PL/Tcl</SPAN >'s standard version of this procedure tries to find a module in <TT CLASS="LITERAL" >pltcl_modules</TT > that will define the required procedure. If one is found, it is loaded into the interpreter, and then execution is allowed to proceed with the originally attempted procedure call. A secondary table <TT CLASS="LITERAL" >pltcl_modfuncs</TT > provides an index of which functions are defined by which modules, so that the lookup is reasonably quick. </P ><P > The <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > distribution includes support scripts to maintain these tables: <TT CLASS="COMMAND" >pltcl_loadmod</TT >, <TT CLASS="COMMAND" >pltcl_listmod</TT >, <TT CLASS="COMMAND" >pltcl_delmod</TT >, as well as source for the standard <TT CLASS="LITERAL" >unknown</TT > module in <TT CLASS="FILENAME" >share/unknown.pltcl</TT >. This module must be loaded into each database initially to support the autoloading mechanism. </P ><P > The tables <TT CLASS="LITERAL" >pltcl_modules</TT > and <TT CLASS="LITERAL" >pltcl_modfuncs</TT > must be readable by all, but it is wise to make them owned and writable only by the database administrator. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="pltcl-trigger.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="pltcl-procnames.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Trigger Procedures in PL/Tcl</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="pltcl.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Tcl Procedure Names</TD ></TR ></TABLE ></DIV ></BODY ></HTML >