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Event trigger functions can be written in PL/Tcl.
<span class="productname">PostgreSQL</span> requires that a function that is
to be called as an event trigger must be declared as a function with no
arguments and a return type of <code class="literal">event_trigger</code>.
</p><p>
The information from the trigger manager is passed to the function body
in the following variables:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="varname">$TG_event</code></span></dt><dd><p>
The name of the event the trigger is fired for.
</p></dd><dt><span class="term"><code class="varname">$TG_tag</code></span></dt><dd><p>
The command tag for which the trigger is fired.
</p></dd></dl></div><p>
</p><p>
The return value of the trigger function is ignored.
</p><p>
Here's a little example event trigger function that simply raises
a <code class="literal">NOTICE</code> message each time a supported command is
executed:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION tclsnitch() RETURNS event_trigger AS $$
elog NOTICE "tclsnitch: $TG_event $TG_tag"
$$ LANGUAGE pltcl;
CREATE EVENT TRIGGER tcl_a_snitch ON ddl_command_start EXECUTE FUNCTION tclsnitch();
</pre><p>
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