use Safe;
#my $stranger_danger = '(?{ system("touch /tmp/foobar") })';
my $stranger_danger = '\d';
my @vals = ( 'a', 'b', 'c', '1', '2' );
my $test_env = new Safe;
$test_env->permit( 'regcomp' );
my $tester = $test_env->wrap_code_ref( sub {
    $_ =~ qr/$stranger_danger/
} );

print "Safely matched ", join( ', ', grep { $tester->( $_ ) } @vals ), "\n";