<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >PL/Perl Event Triggers</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 9.6.21 Documentation" HREF="index.html"><LINK REL="UP" TITLE="PL/Perl - Perl Procedural Language" HREF="plperl.html"><LINK REL="PREVIOUS" TITLE="PL/Perl Triggers" HREF="plperl-triggers.html"><LINK REL="NEXT" TITLE="PL/Perl Under the Hood" HREF="plperl-under-the-hood.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="2021-02-27T18:26:08"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.21 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="PL/Perl Triggers" HREF="plperl-triggers.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="plperl.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 43. PL/Perl - Perl Procedural Language</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="PL/Perl Under the Hood" HREF="plperl-under-the-hood.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="PLPERL-EVENT-TRIGGERS" >43.7. PL/Perl Event Triggers</A ></H1 ><P > PL/Perl can be used to write event trigger functions. In an event trigger function, the hash reference <TT CLASS="VARNAME" >$_TD</TT > contains information about the current trigger event. <TT CLASS="VARNAME" >$_TD</TT > is a global variable, which gets a separate local value for each invocation of the trigger. The fields of the <TT CLASS="VARNAME" >$_TD</TT > hash reference are: <P ></P ></P><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="LITERAL" >$_TD->{event}</TT ></DT ><DD ><P > The name of the event the trigger is fired for. </P ></DD ><DT ><TT CLASS="LITERAL" >$_TD->{tag}</TT ></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 procedure is ignored. </P ><P > Here is an example of an event trigger function, illustrating some of the above: </P><PRE CLASS="PROGRAMLISTING" >CREATE OR REPLACE FUNCTION perlsnitch() RETURNS event_trigger AS $$ elog(NOTICE, "perlsnitch: " . $_TD->{event} . " " . $_TD->{tag} . " "); $$ LANGUAGE plperl; CREATE EVENT TRIGGER perl_a_snitch ON ddl_command_start EXECUTE PROCEDURE perlsnitch();</PRE ><P> </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="plperl-triggers.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="plperl-under-the-hood.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >PL/Perl Triggers</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="plperl.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >PL/Perl Under the Hood</TD ></TR ></TABLE ></DIV ></BODY ></HTML >