M100 to M199 User-Defined Commands Return Value

static void user_defined_add_m_code(int num, double arg1, double arg2)
{
    // num      is the m_code number, typically 00-99 corresponding to M100-M199
    char fmt[EMC_SYSTEM_CMD_LEN];
    EMC_SYSTEM_CMD system_cmd;

    //we call FINISH() to flush any linked motions before the M1xx call, 
    //otherwise they would mix badly
    FINISH();
    strcpy(fmt, user_defined_fmt[user_defined_function_dirindex[num]]);
    strcat(fmt, " %f %f");
    snprintf(system_cmd.string, sizeof(system_cmd.string), fmt, num, arg1, arg2);
    interp_list.append(system_cmd);
}

int emcSystemCmd(char *s)
{
    char buffer[EMC_SYSTEM_CMD_LEN];
    char *argv[EMC_SYSTEM_CMD_LEN / 2 + 1];

    if (0 != emcSystemCmdPid) {
	// something's already running, and we can only handle one
	if (emc_debug & EMC_DEBUG_TASK_ISSUE) {
	    rcs_print
		("emcSystemCmd: abandoning process %d, running ``%s''\n",
		 emcSystemCmdPid, s);
	}
    }

    emcSystemCmdPid = fork();

    if (-1 == emcSystemCmdPid) {
	// we're still the parent, with no child created
	if (emc_debug & EMC_DEBUG_TASK_ISSUE) {
	    rcs_print("system command ``%s'' can't be executed\n", s);
	}
	return -1;
    }

    if (0 == emcSystemCmdPid) {
	// we're the child
	// convert string to argc/argv
	argvize(s, buffer, argv, EMC_SYSTEM_CMD_LEN);
	// drop any setuid privileges
	setuid(getuid());
	execvp(argv[0], argv);
	// if we get here, we didn't exec
	if (emc_debug & EMC_DEBUG_TASK_ISSUE) {
	    rcs_print("emcSystemCmd: can't execute ``%s''\n", s);
	}
	exit(-1);
    }
    // else we're the parent
    return 0;
}