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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>44.7. Event Trigger Functions in PL/Tcl</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="pltcl-trigger.html" title="44.6. Trigger Functions in PL/Tcl" /><link rel="next" href="pltcl-error-handling.html" title="44.8. Error Handling in PL/Tcl" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.7. Event Trigger Functions in PL/Tcl</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pltcl-trigger.html" title="44.6. Trigger Functions in PL/Tcl">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="pltcl.html" title="Chapter 44. PL/Tcl — Tcl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Tcl — Tcl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pltcl-error-handling.html" title="44.8. Error Handling in PL/Tcl">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLTCL-EVENT-TRIGGER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.7. Event Trigger Functions in PL/Tcl <a href="#PLTCL-EVENT-TRIGGER" class="id_link">#</a></h2></div></div></div><a id="id-1.8.9.11.2" class="indexterm"></a><p>
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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