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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 16.2 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>
+    </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pltcl-trigger.html" title="44.6. Trigger Functions in PL/Tcl">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="pltcl.html" title="Chapter 44. PL/Tcl — Tcl Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pltcl-error-handling.html" title="44.8. Error Handling in PL/Tcl">Next</a></td></tr><tr><td width="40%" align="left" valign="top">44.6. Trigger Functions in PL/Tcl </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 44.8. Error Handling in PL/Tcl</td></tr></table></div></body></html>
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