> After hours of search, I searched just some more and I think I found the
> solution, hope it can be useful to someone else :
>
> CREATE LANGUAGE plperlu;
>
> CREATE FUNCTION test_perl_external (integer) RETURNS boolean AS $$
> $filename = '/tmp/somefile';
> if (-e $filename) { return true; }
> return false;
> $$ LANGUAGE plperlu;
>
> SELECT test_perl_external(1);
>
Just remember that anything run like that, won't rollback in a transaction.