readline庫實作指令行自動補全

Linux下應用程式可能需要互動式輸入指令，但普通的标準IO進行指令輸入顯得有些呆闆，人性化不足。本文講述使用libreadline庫，實作類似sh的交換終端：支援指令自動補全，支援曆史指令等。

part1: readline安裝

    （1） 下載下傳readline源碼：http://download.chinaunix.net/download/0009000/8886.shtml

    （2） 解壓後， 在源碼目錄依次執行 ./configure, make, sudo make install 完成安裝

part2：readline使用舉例

#include <stdlib.h>
#include <stdio.h> //注意，readline.h中可能需要調用标準IO庫的内容，是以stdio.h必須在readline.h之前被包含
#include <readline/readline.h>
#include <readline/history.h>

/*
* 真正的指令執行函數
* 測試時，被定義為樁函數了
*/
int com_list(char *para);
int com_view(char *para);
int com_rename(char *para);
int com_stat(char *para);
int com_pwd(char *para);
int com_delete(char *para);
int com_help(char *para);
int com_cd(char *para);
int com_quit(char *para);

/*
* A structure which contains information on the commands this program
* can understand.
*/
typedef struct
{
    char *name;         /* User printable name of the function. */
    rl_icpfunc_t *func; /* Function to call to do the job. */
    char *doc;          /* Documentation for this function. */
} COMMAND;

COMMAND commands[] =
{
    {"cd",     com_cd,     "Change to directory DIR"},
    {"delete", com_delete, "Delete FILE"},
    {"help",   com_help,   "Display this text"},
    {"?",      com_help,   "Synonym for `help'"},
    {"list",   com_list,   "List files in DIR"},
    {"ls",     com_list,   "Synonym for `list'"},
    {"pwd",    com_pwd,    "Print the current working directory"},
    {"quit",   com_quit,   "Quit using Fileman"},
    {"rename", com_rename, "Rename FILE to NEWNAME"},
    {"stat",   com_stat,   "Print out statistics on FILE"},
    {"view",   com_view,   "View the contents of FILE"},
    {(char *)NULL, (rl_icpfunc_t *)NULL, (char *)NULL}
};

int com_list(char *para)
{
    printf("do com_list:%s\n", para);

    ///> add @2020.05.29
    for (unsigned char index = 0x00; index < sizeof(commands)/sizeof(COMMAND); index++)
    {
        printf("Test cli cmd doc is %s\r\n", commands[index].doc);
    }

    return 0;
}

int com_view(char *para)
{
    printf("do com_view:%s\n", para);
    return 0;
}

int com_rename(char *para)
{
    printf("do com_rename:%s\n", para);
    return 0;
}
int com_stat(char *para)
{
    printf("do com_stat:%s\n", para);
    return 0;
}

int com_pwd(char *para)
{
    printf("do com_pwd:%s\n", para);
    return 0;
}
int com_delete(char *para)
{
    printf("do com_delete:%s\n", para);
    return 0;
}
int com_help(char *para)
{
    printf("do com_help:%s\n", para);
    return 0;
}

int com_cd(char *para)
{
    printf("do com_cd:%s\n", para);
    return 0;
}
int com_quit(char *para)
{
    printf("do com_quit:%s\n", para);
    exit(0);
}

char *dupstr(char *s)
{
    char *r;

    r = malloc(strlen(s) + 1);
    strcpy(r, s);
    return (r);
}

// clear up white spaces
char *stripwhite(char *string)
{
    register char *s, *t;

    for (s = string; whitespace(*s); s++)
        ;

    if (*s == 0)
        return (s);

    t = s + strlen(s) - 1;
    while (t > s && whitespace(*t))
        t--;

    *++t = '\0';

    return s;
}

/*
* Look up NAME as the name of a command, and return a pointer to that
* command. Return a NULL pointer if NAME isn't a command name.
*/
COMMAND *find_command(char *name)
{
    register int i;

    for (i = 0; commands[i].name; i++)
        if (strcmp(name, commands[i].name) == 0)
            return (&commands[i]);

    return ((COMMAND *)NULL);
}

/* Execute a command line. */
int execute_line(char *line)
{
    register int i;
    COMMAND *command;
    char *word;

    /* Isolate the command word. */
    i = 0;
    while (line[i] && whitespace(line[i]))
        i++;
    word = line + i;

    while (line[i] && !whitespace(line[i]))
        i++;

    if (line[i])
        line[i++] = '\0';

    command = find_command(word);

    if (!command)
    {
        fprintf(stderr, "%s: No such command for Hytera Cli Framework.\n", word);
        return (-1);
    }

    /* Get argument to command, if any. */
    while (whitespace(line[i]))
        i++;

    word = line + i;

    /* Call the function. */
    return ((*(command->func))(word));
}

/*
* Generator function for command completion. STATE lets us know whether
* to start from scratch; without any state (i.e. STATE == 0), then we
* start at the top of the list.
*/
char *command_generator(const char *text, int state)
{
    static int list_index, len;
    char *name;

    /*
    * If this is a new word to complete, initialize now. This includes
    * saving the length of TEXT for efficiency, and initializing the index
    * variable to 0.
    */
    if (!state)
    {
        list_index = 0;
        len = strlen(text);
    }

    /* Return the next name which partially matches from the command list. */
    while (name = commands[list_index].name)
    {
        list_index++;

        if (strncmp(name, text, len) == 0)
            return (dupstr(name));
    }

    /* If no names matched, then return NULL. */
    return ((char *)NULL);
}

/*
* Attempt to complete on the contents of TEXT. START and END bound the
* region of rl_line_buffer that contains the word to complete. TEXT is
* the word to complete. We can use the entire contents of rl_line_buffer
* in case we want to do some simple parsing. Return the array of matches,
* or NULL if there aren't any.
*/
char **fileman_completion(const char *text, int start, int end)
{
    char **matches;

    matches = (char **)NULL;

    /*
    * If this word is at the start of the line, then it is a command
    * to complete. Otherwise it is the name of a file in the current
    * directory.
    */
    if (start == 0)
        matches = rl_completion_matches(text, command_generator);

    return (matches);
}

/*
* Tell the GNU Readline library how to complete. We want to try to complete
* on command names if this is the first word in the line, or on filenames
* if not.
*/
void initialize_readline()
{
    /* Allow conditional parsing of the ~/.inputrc file. */
    rl_readline_name = ">";

    /* Tell the completer that we want a crack first. */
    rl_attempted_completion_function = fileman_completion;
}

int main(int argc, char **argv)
{
    char *line, *s;

    initialize_readline(); /* Bind our completer. */

    /* Loop reading and executing lines until the user quits. */
    for (;;)
    {
        line = readline("[Cli Framework]$ ");

        if (!line)
            break;

        /*
        * Remove leading and trailing whitespace from the line.
        * Then, if there is anything left, add it to the history list
        * and execute it.
        */
        s = stripwhite(line);
        if (*s)
        {
            add_history(s);
            execute_line(s);
        }

        free(line);
    }
    exit(0);
}
           

注意，編譯的時候需要連接配接readline庫，例如：

gcc  -o  readline_test  readline_test.c   -lreadline -std=c99
           

part3： readline下的IO複用

但是如果我們有多個 IO 要處理，比如既要從一個網絡 IO 中讀資料，又要從标準輸入中讀取指令，上面的方法就不合适了。為了解決這個問題，我們需要自己用 select 函數監控這兩個 IO，當它們可讀的時候通知這兩個子產品中的輸入函數。形象地說，就是把資料“喂給”這兩個子產品。這樣的模式需要 readline 提供“被動喂給”的工作方式。這種工作方式在 readline 中已有實作。首先，我們需要往 readline 注冊回調函數，當 readline 讀取到一行後，這個回調函數将被調用:

rl_callback_handler_install ("prompt> ", handle_command);
           

接下去，在主事件循環中，我們需要調用 rl_callback_read_char() 通知 readline 去讀取一個字元。下面給一個例子：

static void handle_command (char *line)
{
    ...
}
 
int
main (int argc, char **argv)
{
    int netfd
    fd_set allfd;
    int maxfd;
 
    netfd = connect_to_server ();
 
 
    FD_ZERO (&allfd);
    FD_SET (fileno(stdin), &allfd);
    FD_SET (netfd, &allfd);
    maxfd = netfd;
 
    rl_callback_handler_install ("ccnet> ", handle_command);
 
    while (1) {
        fd_set rfds;
        int retval;
 
        rfds = allfd;
 
        retval = select (maxfd + 1, &rfds, NULL, NULL, NULL);
        if (retval < 0)
            perror ("select");
 
        if (FD_ISSET(0, &rfds))
            rl_callback_read_char();
 
        if (FD_ISSET(netfd, &rfds))
            read_from_network (netfd);
    }
}
           

關于readline更多的使用請自行閱讀readline的man檔案。