#!/usr/bin/perl --
use Safe;
my $safe = Safe->new;
for my $val ( qw/ bye hi / ){
    local $_ = $val;
    my $ret = $safe->reval(q{
        return 1 if /bye/;
        return 0 if /hi/;
    });
    print "$val => $ret\n";
}
$safe->reval(q{ system(); }) or die $@;
__END__
bye => 1
hi => 0
'system' trapped by operation mask at (eval 9) line 1.