#!/usr/bin/perl
use Safe;
use IO::File;

my $code =<<'END';
    my $a = '';
    my $f = IO::File->new('/etc/passwd');
    while (my $l = $f->getline) { $a .= $l }
    return $a;
END
my $compartment = Safe->new;
$safe = sub { $compartment->reval($code) || die $@};
print $safe->();