astrcatf
astrcatf(&buf, "%s/%s", subcmd_config.prefix, path);
astrcatf(&buf, "%s/", path);
astrcatf(&buf, "%s %s [<options>] {", subcmd_config.exec_name, argv[0]);
astrcatf(&error_buf, "unknown option `%s'",
astrcatf(&error_buf, "unknown switch `%c'", *ctx.opt);