“命令终端”的实现3-命令的执行

前面已经能获取到输入的字符了，接着就是解析这些字符，判断，符合要求的，执行对应的函数。而对应的函数，就是需要实现的命令。本文从具体的命令实现逐步倒推，最后对接上一文章。

一、命令函数

Linux 中，基本上每条命令都有参数及帮助信息，仿照这些功能，给出实现函数指针及结构体：

/** Monitor Command Table*/
typedef int (*cmd_func)(int argc, char * const argv[]);struct cmd_tbl_s {char    *name;        /* Command Name            */int     maxargs;    /* maximum number of arguments    */cmd_func cmd;       /* Implementation function    */char    *usage;        /* Usage message    (short)    */
#ifdef    CONFIG_SYS_LONGHELPchar    *help;    /* Help  message    (long)    */
#endif
#ifdef CONFIG_AUTO_COMPLETE/* do auto completion on the arguments */int     (*complete)(int argc, char * const argv[], char last_char, int maxv, char *cmdv[]);
#endif
};typedef struct cmd_tbl_s    cmd_tbl_t;/* someone should implement the table */
extern cmd_tbl_t cmd_table[];

为保持命令的独立性，设置cmd_func函数指针。命令结构体为全局变量，下面给出其定义及对应命令的实现：


/* just a foolish command table */
cmd_tbl_t cmd_table[] =
{{"help", CONFIG_SYS_MAXARGS, do_help, "print help info."},{"print", 1, do_print, "print the env."},{"exit", 1, do_exit, "exit..."},{NULL, 0, NULL, NULL},
};int do_help(int argc, char * const argv[])
{_do_help(cmd_table, sizeof(cmd_table)/sizeof(cmd_tbl_t), argc, argv);return 0;
}int do_print(int argc, char * const argv[])
{myprintf("in %s\n", __FUNCTION__);return 0;
}int do_exit(int argc, char * const argv[])
{exit(0);return 0;
}

以上就是具体命令的实现过程，可以将每条命令都理解为一个单独的可带参数的程序。

二、查找命令

查找命令名称前，需要先对输入的字符串进行解析，实现函数如下：

int parse_line (char *line, char *argv[])
{int nargs = 0;#ifdef DEBUG_PARSERcmd_printf ("parse_line: \"%s\"\n", line);
#endifwhile (nargs < CONFIG_SYS_MAXARGS){/* skip any white space */while ((*line == ' ') || (*line == '\t')){++line;}if (*line == '\0'){    /* end of line, no more args    */argv[nargs] = NULL;
#ifdef DEBUG_PARSERcmd_printf ("parse_line: nargs=%d\n", nargs);
#endifreturn (nargs);}argv[nargs++] = line;    /* begin of argument string    *//* find end of string */while (*line && (*line != ' ') && (*line != '\t')){++line;}if (*line == '\0'){    /* end of line, no more args    */argv[nargs] = NULL;
#ifdef DEBUG_PARSERcmd_printf ("parse_line: nargs=%d\n", nargs);
#endifreturn (nargs);}*line++ = '\0';        /* terminate current arg     */}cmd_printf ("** Too many args (max. %d) **\n", CONFIG_SYS_MAXARGS);#ifdef DEBUG_PARSERcmd_printf ("parse_line: nargs=%d\n", nargs);
#endifreturn (nargs);
}

输出参数为argv数组，此即为命令参数列表，其中argv[0]即命令名称，返回值为命令参数个数，即argc。这就是我们熟悉的C语言 main 函数的参数。

查找命令实际是搜索结构体数组cmd_table中的命令名称。如果找到返回名称，反之为空。

cmd_tbl_t* find_cmd_tbl3(const char* cmd, cmd_tbl_t *table)
{const char *p;char *q;cmd_tbl_t *c, *found;int nmatches, longest;longest = 0;nmatches = 0;found = 0;for (c = table; (p = c->name) != NULL; c++){for (q = cmd; *q == *p++; q++)if (*q == 0)        /* exact match? */return (c);if (!*q){return NULL;}}return NULL;
}cmd_tbl_t *find_cmd (const char* cmd)
{//int len = sizeof(cmd_table) / sizeof(cmd_tbl_t);//return find_cmd_tbl(cmd, cmd_table, len);//return find_cmd_tbl2(cmd, cmd_table);return find_cmd_tbl3(cmd, cmd_table);
}

注意，如果命令数量过多，不宜使用从头遍历的方法查找。本文工程仅为示例，暂不研究效率。

三、汇总运行

运行命令函数实现如下，

int run_command (const char *cmd)
{cmd_tbl_t *cmdtp;char cmdbuf[CB_SIZE];    /* working copy of cmd        */char *token;            /* start of token in cmdbuf    */char *sep;            /* end of token (separator) in cmdbuf *///char finaltoken[CB_SIZE];char *str = cmdbuf;char *argv[CONFIG_SYS_MAXARGS + 1];    /* NULL terminated    */int argc, inquotes;int repeatable = 1;int rc = 0;#ifdef DEBUG_PARSERcmd_printf ("[RUN_COMMAND] cmd[%p]=\"", cmd);cmd_puts (cmd ? cmd : "NULL");    /* use puts - string may be loooong */cmd_puts ("\"\n");
#endif//clear_ctrlc();        /* forget any previous Control C */if (!cmd || !*cmd){return -1;    /* empty command */}if (strlen(cmd) >= CB_SIZE){cmd_puts ("## Command too long!\n");return -1;}strcpy (cmdbuf, cmd);/* Process separators and check for invalid* repeatable commands*/#ifdef DEBUG_PARSERcmd_printf ("[PROCESS_SEPARATORS] %s\n", cmd);
#endifwhile (*str) {/** Find separator, or string end* Allow simple escape of ';' by writing "\;"*/for (inquotes = 0, sep = str; *sep; sep++){if ((*sep=='\'') &&(*(sep-1) != '\\'))inquotes=!inquotes;if (!inquotes &&(*sep == ';') &&    /* separator        */( sep != str) &&    /* past string start    */(*(sep-1) != '\\'))    /* and NOT escaped    */break;}/** Limit the token to data between separators*/token = str;if (*sep){str = sep + 1;    /* start of command for next pass */*sep = '\0';}elsestr = sep;    /* no more commands for next pass */
#ifdef DEBUG_PARSERcmd_printf ("token: \"%s\"\n", token);
#endif/* Extract arguments */if ((argc = parse_line (token, argv)) == 0){rc = -1;    /* no command at all */continue;}/* Look up command in command table */if ((cmdtp = find_cmd(argv[0])) == NULL){cmd_printf ("Unknown command '%s' - try 'help'\n", argv[0]);rc = -1;    /* give up after bad command */continue;}/* found - check max args */if (argc > cmdtp->maxargs){cmd_usage(cmdtp);rc = -1;continue;}/* OK - call function to do the command */if ((cmdtp->cmd) (argc, argv) != 0){rc = -1;}}//return rc ? rc : repeatable;return rc;
}

主要过程有解析字符串parse_line，查找命令结构数组find_cmd，最后运行函数指针。

四、主函数

入口函数及倒计时函数如下：

int abortboot(int delay)
{int abort = 0;int i = 0;myprintf("Hit any key to stop autoboot: %2d ", delay);while ((delay > 0) && (!abort)){--delay;for (i = 0; !abort && i < 100; ++i){if (mytstc()){abort = 1;delay = 0;mygetc();break;}mysleep(10);}myprintf("\b\b\b%2d ", delay);}myputc('\n');return abort;
}int readline_test(void)
{static char lastcommand[CB_SIZE] = {0};int len;if (!abortboot(5)){myprintf("Aotu run.\n");return 0;}myprintf("You abort.\n");while (1){len = readline(PROMPT, lastcommand);if (len > 0){//printf("len: %d\n", len);if (len >= CB_SIZE){myprintf("command line too large.\n");break;}//strcpy(lastcommand, console_buffer);//printf("[echo]: %s\n", lastcommand);}else if (len == 0){//printf("nothing input.\n");// do nothing}if (len == -1){myputs("<INTERRUPT>\n");}else{run_command(lastcommand);}}return 0;
}

至此，一个“命令终端”实现完毕。可对其底层的字符处理进行修改，以适应不同环境。除此外，其它业务逻辑完全无变化。

李迟 2020.9.30