In the psql
console, use \ef
with the name of a function to fetch and
open the definition of the function. The function will be opened in your
system $EDITOR
in the form of a create or replace function
query.
Executing
> \ef now
will open the following in your default editor
CREATE OR REPLACE FUNCTION pg_catalog.now()
RETURNS timestamp with time zone
LANGUAGE internal
STABLE STRICT
AS $function$now$function$