sub main::BEGIN { print "X\n" }

##</code><code>##

*main::BEGIN = sub { print "X\n" };
&BEGIN; 

##</code><code>##

*main::BEGIN = sub { print "X\n" };
BEGIN();

##</code><code>##

*main::BEGIN = sub () { print "X\n" };
BEGIN();

##</code><code>##

 
perl -e 'BEGIN'    # Syntax error. 
perl -e 'BEGIN;    # No error.
perl -e 'BEGIN()'  # Syntax error.
perl -e 'BEGIN();' # No error.