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<title>37.7.Modules and the unknown command</title>
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<a name="pltcl-unknown"></a>37.7.Modules and the <code class="function">unknown</code> command</h2></div></div></div>
<p> PL/Tcl has support for autoloading Tcl code when used.
It recognizes a special table, <code class="literal">pltcl_modules</code>, which
is presumed to contain modules of Tcl code. If this table
exists, the module <code class="literal">unknown</code> is fetched from the table
and loaded into the Tcl interpreter immediately after creating
the interpreter.
</p>
<p> While the <code class="literal">unknown</code> 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 <code class="literal">pltcl_modules</code>
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 <code class="literal">pltcl_modfuncs</code> 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:
<code class="command">pltcl_loadmod</code>, <code class="command">pltcl_listmod</code>,
<code class="command">pltcl_delmod</code>, as well as source for the standard
<code class="literal">unknown</code> module in <code class="filename">share/unknown.pltcl</code>. This module
must be loaded
into each database initially to support the autoloading mechanism.
</p>
<p> The tables <code class="literal">pltcl_modules</code> and <code class="literal">pltcl_modfuncs</code>
must be readable by all, but it is wise to make them owned and
writable only by the database administrator.
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