> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/server-programming/pltcl/pltcl-event-trigger.md).

# 42.7. Event Trigger Functions in PL/Tcl \#

Event trigger functions can be written in PL/Tcl. PostgreSQL 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 `event_trigger`.

The information from the trigger manager is passed to the function body in the following variables:

`$TG_event` : The name of the event the trigger is fired for.

`$TG_tag` : The command tag for which the trigger is fired.

The return value of the trigger function is ignored.

Here's a little example event trigger function that simply raises a `NOTICE` message each time a supported command is executed:

```

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();
```

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/pltcl-event-trigger.html)（英文原文，待翻譯）


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