libreadline-dev是做什么用的，能给我举个例子吗？

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作者：basilguo@163.com日期：2023年8月15日描述：libreadline-dev库介绍及示例简介：在实现类shell程序时，可能需要使用到命令补全及命令历史记录。这时，可以使用libreadline库。

Author basilguo@163.com

Date Aug. 15, 2023

Description libreadline-dev介绍和例子

简介

在实现一个类shell的程序的时候，可能需要使用到命令补全以及命令历史记录。这时候就可以使用libreadline库，这是一个GNU开发的库，官网是：The GNU Readline Library。

这个库主要提供命令补全、命令修改以及命令历史，当然命令历史有一个单独的库叫做History library，但这里就一起装一起用了，而且包管理器也没有区分（apt show libreadline-dev可以查看依赖包）。

当然最好的教程就是官网的文档。第一部分算是介绍，第二部分是开发，上面也给了很多例子，可以直接照抄了。

安装

• apt系：sudo apt install libreadline-dev
• yum系：sudo yum install readline-devel
• 源码：没试过，下面是我猜测的，不过GNU的源码安装都基本是同样命令

  git clone git://git.savannah.gnu.org/readline.git ./configure make sudo make install sudo ldconfig

使用

它主要有两个头文件，<readline/readline.h>和<readline/history.h>，前者就是命令行编辑、命令补全等，后者就是命令历史。如果要查看所有的头文件，那就去/usr/include/readline/下查看。

默认情况下，readline只提供对文件名的补全。这个例子介绍了下，主要就两个函数：

• readline(prompt_string)：获取用户输入，可以补全文件名
• add_history(input_string)：用户输入加入历史，可以使用上下箭头进行切换。

但是使用readline一般是为了自定义命令。这个例子的源码在GNU Readline Library的教程库中，叫做fileman.c。我重新整理了下这个例子，原来的函数参数写法好像是C标准还没有成立时的写法，不过无所谓了，是能看懂的。

在这个例子中，其实主要还是看readline相关的函数吧，其它的再学习。例子中，定义了一个COMMAND数据结构，然后定义了该数据结构的数组，描述各个命令、执行函数以及对应含义。在这个例子中和readline相关：

• 一个是add_history，就是把命令加入历史记录。
• 一个是rl_attempted_completion_function，这是一个指针变量，指向命令补全的函数，这个函数fileman_completion中text就是用户已输入，start和end为在rl_line_buffer中的边界。start不一定为0，那是因为命令补全不一定是从第一个单词开始的。例如ls bu，要补全为build，那么start就是3，end是5。
• 一个是rl_completion_matches，创建matches，相当于是返回的是所有匹配的命令以及文件。如果没有输入，就返回所有的命令了；部分输入有匹配返回匹配，没有匹配返回NULL。
• 当然还有一堆的执行函数，以com_开头，那就是具体的命令的逻辑了。

简单编译使用

gcc -o fileman fileman.c -I/usr/include/readline -lreadline

更多功能还是参考官网文档吧。

• GNU Readline Library
• The GNU Readline Library
• The GNU History Library
• The GNU Readline User Interface

源码

<details> <summary>fileman.c整理后的源码</summary>

/* readline exmaple code getting from * tiswww.case.edu/php/chet/readline/readline.html#A-Short-Completion-Example */ /* fileman.c -- A tiny application which demonstrates how to use the * GNU Readline library. This application interactively allows users * to manipulate files and their modes. */ #include <sys/types.h> #include <sys/file.h> #include <sys/stat.h> #include <unistd.h> #include <fcntl.h> #include <stdio.h> #include <errno.h> #include <locale.h> #include <string.h> #include <stdlib.h> #include <time.h> #include <readline/readline.h> #include <readline/history.h> /* The name of this program, as taken from argv[0]. */ static char *progname; /* When non-zero, this global means the user is done using this program. */ static int done; /* String to pass to system (). This is for the LIST, VIEW and RENAME * commands. */ static char syscom[1024]; /* The names of functions that actually do the manipulation. */ int com_list(char *); int com_view(char *); int com_rename(char *); int com_stat(char *); int com_pwd(char *); int com_delete(char *); int com_help(char *); int com_cd(char *); int com_quit(char *); /* 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; /* commands array */ 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 } }; /* 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 FileMan.\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)); } /* Strip whitespace from the start and end of STRING. Return a pointer * into STRING. */ 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; } /* Function which tells you that you can't do this. */ void too_dangerous (char *caller) { fprintf (stderr, "%s: Too dangerous for me to distribute. Write it yourself.\n", caller); } /* **************************************************************** */ /* */ /* Interface to Readline Completion */ /* */ /* **************************************************************** */ /* 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 (strdup(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 = "FileMan"; /* Tell the completer that we want a crack first. */ rl_attempted_completion_function = fileman_completion; } /* Return non-zero if ARG is a valid argument for CALLER, else print * an error message and return zero. */ int valid_argument (char *caller, char *arg) { if (!arg || !*arg) { fprintf (stderr, "%s: Argument required.\n", caller); return (0); } return (1); } /* **************************************************************** */ /* */ /* FileMan Commands */ /* */ /* **************************************************************** */ /* List the file(s) named in arg. */ int com_list (char *arg) { if (!arg) arg = ""; sprintf (syscom, "ls -FClg %s", arg); return (system (syscom)); } int com_view (char *arg) { if (!valid_argument ("view", arg)) return 1; #if defined (__MSDOS__) /* more.com doesn't grok slashes in pathnames */ sprintf (syscom, "less %s", arg); #else sprintf (syscom, "more %s", arg); #endif return (system (syscom)); } int com_rename (char *arg) { too_dangerous ("rename"); return (1); } int com_stat (char *arg) { struct stat finfo; if (!valid_argument ("stat", arg)) return (1); if (stat (arg, &finfo) == -1) { perror (arg); return (1); } printf ("Statistics for `%s':\n", arg); printf ("%s has %ld link%s, and is %ld byte%s in length.\n", arg, finfo.st_nlink, (finfo.st_nlink == 1) ? "" : "s", finfo.st_size, (finfo.st_size == 1) ? "" : "s"); printf ("Inode Last Change at: %s", ctime (&finfo.st_ctime)); printf (" Last access at: %s", ctime (&finfo.st_atime)); printf (" Last modified at: %s", ctime (&finfo.st_mtime)); return (0); } int com_delete (char *arg) { too_dangerous ("delete"); return (1); } /* Print out help for ARG, or for all of the commands if ARG is * not present. */ int com_help (char *arg) { register int i; int printed = 0; for (i = 0; commands[i].name; i++) { if (!*arg || (strcmp (arg, commands[i].name) == 0)) { printf ("%s\t\t%s.\n", commands[i].name, commands[i].doc); printed++; } } if (!printed) { printf ("No commands match `%s'. Possibilities are:\n", arg); for (i = 0; commands[i].name; i++) { /* Print in six columns. */ if (printed == 6) { printed = 0; printf ("\n"); } printf ("%s\t", commands[i].name); printed++; } if (printed) printf ("\n"); } return (0); } /* Change to the directory ARG. */ int com_cd (char *arg) { if (chdir (arg) == -1) { perror (arg); return 1; } com_pwd (""); return (0); } /* Print out the current working directory. */ int com_pwd (char *ignore) { char dir[1024], *s; s = getcwd (dir, sizeof(dir) - 1); if (s == 0) { printf ("Error getting pwd: %s\n", dir); return 1; } printf ("Current directory is %s\n", dir); return 0; } /* The user wishes to quit using this program. Just set DONE non-zero. */ int com_quit (char *arg) { done = 1; return (0); } int main (int argc, char **argv) { char *line, *s; setlocale (LC_ALL, ""); progname = argv[0]; initialize_readline (); /* Bind our completer. */ /* Loop reading and executing lines until the user quits. */ for ( ; done == 0; ) { line = readline ("FileMan: "); 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); }

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