--agi.h
typedef struct agi_command {
        /* Null terminated list of the words of the command */
        char *cmda[AST_MAX_CMD_LEN];
        /* Handler for the command (channel, AGI state, # of arguments, argument list).
            Returns RESULT_SHOWUSAGE for improper arguments */
        int (*handler)(struct ast_channel *chan, AGI *agi, int argc, char *argv[]);
        /* Summary of the command (< 60 characters) */
        char *summary;
        /* Detailed usage information */
        char *usage;
        int dead;
        AST_LIST_ENTRY(agi_command_ll) list;
} agi_command;

--res_agi.c
AST_RWLIST_HEAD_STATIC(agi_commands, agi_command);

static int help_workhorse(int fd, char *match[])
{
	char fullcmd[80], matchstr[80];
	int x;
	struct agi_command *temp_command;

	if (match)
		ast_join(matchstr, sizeof(matchstr), match);

	ast_cli(fd, "%5.5s %20.20s   %s\n","Dead","Command","Description");
	AST_RWLIST_RDLOCK(&agi_commands);
	AST_RWLIST_TRAVERSE(&agi_commands, temp_command, list) {
		if (!temp_command->cmda[0])
			break;
		// Hide commands that start with '_'
		if ((temp_command->cmda[0])[0] == '_')
			continue;
		ast_join(fullcmd, sizeof(fullcmd), temp_command->cmda);
		if (match && strncasecmp(matchstr, fullcmd, strlen(matchstr)))
			continue;
		ast_cli(fd, "%5.5s %20.20s   %s\n", temp_command->dead ? "Yes" : "No" , fullcmd, temp_command->summary);    
  }
	AST_RWLIST_UNLOCK(&agi_commands);
	return 0;
}