Perl: Ovverride core perl routines

CoreTest.pl

#!/usr/bin/env perl

# See my post on http://stackoverflow.com/questions/33725298/perl-disable-shell-access
# Ref: https://github.com/Perl/perl5/blob/blead/lib/CORE.pod

BEGIN {
    *CORE::GLOBAL::system = sub {
      die('Do not use system calls.');
    };

    *CORE::GLOBAL::exec = sub {
      die('Do not use exec.');
    };

    *CORE::GLOBAL::readpipe = sub {
      die('Do not use back ticks.');
    };
}

#...
my $out = system('ls -lah'); # I will die at this point, but not before
print $out;