-- test plperl.on_plperl_init errors are fatal
-- Avoid need for custom_variable_classes = 'plperl'
LOAD 'plperl';
SET SESSION plperl.on_plperl_init = ' system("/nonesuch") ';
SHOW plperl.on_plperl_init;
 plperl.on_plperl_init 
-----------------------
  system("/nonesuch") 
(1 row)

DO $$ warn 42 $$ language plperl;
ERROR:  'system' trapped by operation mask at line 2.
CONTEXT:  while executing plperl.on_plperl_init
PL/Perl anonymous code block