io.c:2214
static VALUE
rb_io_s_popen(argc, argv, klass)
    int argc;
    VALUE *argv;
    VALUE klass;
{
    char *str = 0;

    if (argc >= 1) {
	str = StringValuePtr(argv[0]);
    }
    return rb_io_popen(str, argc, argv, klass);
}
