Linux系统命令“ls -l”的实现
一、基本概念
1. “ls -l”所显示各项的意义
例：-rw-rw-r-- 1 using using 3102 7月 22 17:06 test.c
drwxrwxr-x 2 using using 4096 7月 22 18:39 testdir
lrwxrwxrwx 1 using using 17 7月 22 18:43 shared -> /media/sf_shared/
第一字段：首字母代表的是文件类型 ，其中"-"为普通文件、"d"为目录文件、"c"为字符设备文件、"b"为块设备文件、"p"为管道文件、"l"为链接文件、"s"为socket文件。三个“rwx”依次代表文件所有者、文件所有者所在用户组、其它用户对文件拥有的权限。“rwx”分别代表拥有读、写和执行权限，“-”代表无对应权限。
第二字段：文件硬连接数量
第三字段：文件拥有者
第四字段：文件拥有者所在组
第五字段：文件大小（以字节为单位）
第六字段：文件最后更改时间
第七字段：文件名（若为连接文件则追加显示其源文件的路径）
二、重要函数与结构体
1. 目录操作函数
1 #include <sys/types.h>
2 #include <dirent.h>
3
4 DIR *opendir(const char *name);
5 DIR *fdopendir(int fd);
6
7
8 #include <dirent.h>
9
10 struct dirent *readdir(DIR *dirp);
11
12 struct dirent {
13 ino_t d_ino; /* inode number */
14 off_t d_off; /* offset to the next dirent */
15 unsigned short d_reclen; /* length of this record */
16 unsigned char d_type; /* type of file; not supported by all file system types */
17 char d_name[256]; /* filename */
18 };
2. 获取文件信息
这里必须使用int lstat(const char *path, struct stat *buf);函数，否则在处理链接文件时会将其链接的原文件作为处理对象，而不是它本身。
1 #include <sys/types.h>
2 #include <sys/stat.h>
3 #include <unistd.h>
4
5 int stat(const char *path, struct stat *buf);
6 int fstat(int fd, struct stat *buf);
7 int lstat(const char *path, struct stat *buf);
8
9 struct stat {
10 dev_t st_dev; /* ID of device containing file */
11 ino_t st_ino; /* inode number */
12 mode_t st_mode; /* protection */
13 nlink_t st_nlink; /* number of hard links */
14 uid_t st_uid; /* user ID of owner */
15 gid_t st_gid; /* group ID of owner */
16 dev_t st_rdev; /* device ID (if special file) */
17 off_t st_size; /* total size, in bytes */
18 blksize_t st_blksize; /* blocksize for file system I/O */
19 blkcnt_t st_blocks; /* number of 512B blocks allocated */
20 time_t st_atime; /* time of last access */
21 time_t st_mtime; /* time of last modification */
22 time_t st_ctime; /* time of last status change */
23 };
3. 文件类型及权限的判断
1 The following POSIX macros are defined to check the file type using the st_mode field: 2 3 S_ISREG(m) is it a regular file? 4 S_ISDIR(m) directory? 5 S_ISCHR(m) character device? 6 S_ISBLK(m) block device? 7 S_ISFIFO(m) FIFO (named pipe)? 8 S_ISLNK(m) symbolic link? (Not in POSIX.1-1996.) 9 S_ISSOCK(m) socket? (Not in POSIX.1-1996.) 10 11 12 The following flags are defined for the st_mode field: 13 14 S_IFMT 0170000 bit mask for the file type bit fields 15 S_IFSOCK 0140000 socket 16 S_IFLNK 0120000 symbolic link 17 S_IFREG 0100000 regular file 18 S_IFBLK 0060000 block device 19 S_IFDIR 0040000 directory 20 S_IFCHR 0020000 character device 21 S_IFIFO 0010000 FIFO 22 S_ISUID 0004000 set UID bit 23 S_ISGID 0002000 set-group-ID bit (see below) 24 S_ISVTX 0001000 sticky bit (see below) 25 S_IRWXU 00700 mask for file owner permissions 26 S_IRUSR 00400 owner has read permission 27 S_IWUSR 00200 owner has write permission 28 S_IXUSR 00100 owner has execute permission 29 S_IRWXG 00070 mask for group permissions 30 S_IRGRP 00040 group has read permission 31 S_IWGRP 00020 group has write permission 32 S_IXGRP 00010 group has execute permission 33 S_IRWXO 00007 mask for permissions for others (not in group) 34 S_IROTH 00004 others have read permission 35 S_IWOTH 00002 others have write permission 36 S_IXOTH 00001 others have execute permission
4. 文件用户ID与用户所在组ID的转换
1 #include <sys/types.h>
2 #include <pwd.h>
3
4 struct passwd *getpwnam(const char *name);
5 struct passwd *getpwuid(uid_t uid);
6 int getpwnam_r(const char *name, struct passwd *pwd,char *buf, size_t buflen, struct passwd **result);
7 int getpwuid_r(uid_t uid, struct passwd *pwd,char *buf, size_t buflen, struct passwd **result);
8
9
10 The passwd structure is defined in <pwd.h> as follows:
11
12 struct passwd {
13 char *pw_name; /* username */
14 char *pw_passwd; /* user password */
15 uid_t pw_uid; /* user ID */
16 gid_t pw_gid; /* group ID */
17 char *pw_gecos; /* user information */
18 char *pw_dir; /* home directory */
19 char *pw_shell; /* shell program */
20 };
1 #include <sys/types.h>
2 #include <grp.h>
3
4 struct group *getgrnam(const char *name);
5 struct group *getgrgid(gid_t gid);
6 int getgrnam_r(const char *name, struct group *grp,char *buf, size_t buflen, struct group **result);
7 int getgrgid_r(gid_t gid, struct group *grp,char *buf, size_t buflen, struct group **result);
8
9
10 The group structure is defined in <grp.h> as follows:
11
12 struct group {
13 char *gr_name; /* group name */
14 char *gr_passwd; /* group password */
15 gid_t gr_gid; /* group ID */
16 char **gr_mem; /* group members */
17 };
5. 文件最后修改时间
1 #include <time.h>
2
3 struct tm *localtime(const time_t *timep);
4 struct tm *localtime_r(const time_t *timep, struct tm *result);
5
6
7 Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
8
9 struct tm {
10 int tm_sec; /* seconds */
11 int tm_min; /* minutes */
12 int tm_hour; /* hours */
13 int tm_mday; /* day of the month */
14 int tm_mon; /* month */
15 int tm_year; /* year */
16 int tm_wday; /* day of the week */
17 int tm_yday; /* day in the year */
18 int tm_isdst; /* daylight saving time */
19 };
三、执行结果及对比
四、优点与改进方向
本博是在博友“Apollon_krj”的一篇博客“Linux&C编程之Linux系统命令“ls -l”的简单实现”的基础上改进完成。总体沿用了原有思路和框架，做了以下改良：
1. 可以处理软连接文件（原处理链接文件所链接的原文件）；
2. 当输入“myls -l”指令时默认显示当前目录下文件的详细信息（原报错）；
3. 指令、代码优化。
但目前暂未实现总用量/total、模糊匹配和彩字显示功能，有兴趣的朋友可以尝试一下。
五、实现代码
1. myls.h
1 #ifndef _MYLS_H_ 2 #define _MYLS_H_ 3 4 #include<stdio.h> 5 #include<stdlib.h> 6 #include<string.h> 7 #include<unistd.h> 8 #include<dirent.h> 9 #include<sys/stat.h> 10 #include<sys/types.h> 11 #include<fcntl.h> 12 #include<time.h> 13 #include<pwd.h> 14 #include<grp.h> 15 16 // 处理错误 17 void error_printf(const char* ); 18 19 // 处理路径下的文件 20 void list_dir(const char* ); 21 void list_message(const char* , const struct stat*); 22 23 // 所显示的文件信息 24 void file_type(const struct stat* ); 25 void file_power(const struct stat* ); 26 // printf st_nlink 27 void file_id(const struct stat* ); 28 // printf st_size 29 void file_mtime(const struct stat* ); 30 // printf filename 31 void link_printf(const char* ); 32 33 #endif//_MYLS_H_
2. myls.c
1 #include "myls.h"
2
3 // 处理错误
4 void error_printf(const char* funname)
5 {
6 perror(funname);
7 exit(EXIT_FAILURE);
8 /*
9 * EXIT_SUCCESS和EXIT_FAILURE是两个常量。
10 * EXIT_SUCCESS=0，EXIT_FAILURE=1。
11 * 0表示程序寿终正寝，1表示死于非命。
12 */
13 }
14
15 // 读取路径下的文件
16 void list_dir(const char* pathname)
17 {
18 DIR* ret_opendir = opendir(pathname); // 打开目录"pathname"
19 if(ret_opendir == NULL)
20 error_printf("opendir");
21
22 int ret_chdir = chdir(pathname); // 改变工作目录至"pathname"，便于stat函数的使用
23 if(ret_chdir == -1)
24 error_printf("chdir");
25
26 struct dirent* ret_readdir = NULL; // 定义readdir函数返回的结构体变量
27 while(ret_readdir = readdir(ret_opendir)) // 判断是否读取到目录尾
28 {
29 char* filename = ret_readdir->d_name; // 获取文件名
30 struct stat file_message = {}; // 定义stat函数返回的结构体变量
31 int ret_stat = lstat(filename, &file_message); // 获取文件信息
32 if(ret_stat == -1) // stat读取文件错误则输出提示信息
33 printf("%s error!", filename);
34 else if(strcmp(filename,".") && strcmp(filename,"..")) // 不输出当前目录与上一级目录
35 list_message(filename, &file_message);
36 }
37 }
38
39 // 打印所读取文件的信息
40 void list_message(const char* filename, const struct stat* file_message)
41 {
42 file_type(file_message); // 判断打印文件类型
43 file_power(file_message); // 判断并打印文件权限
44 printf("%d ", file_message->st_nlink); // 打印硬链接数
45 file_id(file_message); // 转换并打印用户id与组id
46 printf("%5ld ", file_message->st_size); // 打印文件大小
47 file_mtime(file_message); // 打印文件最后修改时间
48 printf("%s ", filename); // 打印文件名
49 if(S_ISLNK(file_message->st_mode)) // 如果是软链接文件，打印其指向的位置
50 link_printf(filename);
51 puts("");
52 }
53
54
55 // 所显示的文件信息
56 void file_type(const struct stat* file_message)
57 {
58 //mode_t mode = (*get_message).st_mode;
59 mode_t mode = file_message->st_mode;
60
61 if (S_ISREG(mode)) printf("-"); // 普通文件
62 else if(S_ISDIR(mode)) printf("d"); // 目录文件
63 else if(S_ISCHR(mode)) printf("c"); // 字符设备文件
64 else if(S_ISBLK(mode)) printf("b"); // 块设备文件
65 else if(S_ISFIFO(mode)) printf("p"); // 管道文件
66 else if(S_ISLNK(mode)) printf("l"); // 链接文件
67 else printf("s"); // socket文件
68 }
69
70 void file_power(const struct stat* file_message)
71 {
72 mode_t mode = file_message->st_mode;
73
74 // 判断USR权限
75 printf("%c", mode&S_IRUSR?‘r‘:‘-‘);
76 printf("%c", mode&S_IWUSR?‘w‘:‘-‘);
77 printf("%c", mode&S_IXUSR?‘x‘:‘-‘);
78
79 // 判断GRP权限
80 printf("%c", mode&S_IRGRP?‘r‘:‘-‘);
81 printf("%c", mode&S_IWGRP?‘w‘:‘-‘);
82 printf("%c", mode&S_IXGRP?‘x‘:‘-‘);
83
84 // 判断OTH权限
85 printf("%c", mode&S_IROTH?‘r‘:‘-‘);
86 printf("%c", mode&S_IWOTH?‘w‘:‘-‘);
87 printf("%c ", mode&S_IXOTH?‘x‘:‘-‘);
88 }
89
90 void file_id(const struct stat* file_message)
91 {
92 // 根据用户id获取用户名
93 struct passwd* pwd;
94 pwd = getpwuid(file_message->st_uid);
95 printf("%s ",pwd->pw_name);
96
97 // 根据组id获取组名
98 struct group* grp;
99 grp = getgrgid(file_message->st_gid);
100 printf("%s ",grp->gr_name);
101
102 #if 0
103 struct passwd
104 {
105 char * pw_name; /* Username, POSIX.1 */
106 char * pw_passwd; /* Password */
107 __uid_t pw_uid; /* User ID, POSIX.1 */
108 __gid_t pw_gid; /* Group ID, POSIX.1 */
109 char * pw_gecos; /* Real Name or Comment field */
110 char * pw_dir; /* Home directory, POSIX.1 */
111 char * pw_shell; /* Shell Program, POSIX.1 */
112 };
113
114 struct group
115 {
116 char *gr_name; /* Group name */
117 char *gr_passwd; /* password */
118 __gid_t gr_gid; /* Group ID */
119 char **gr_mem; /* Member list */
120 }
121 #endif//0
122 }
123
124 void file_mtime(const struct stat* file_message)
125 {
126 struct tm* t = localtime(&file_message->st_mtime);
127 printf("%2d月 %2d %02d:%02d ", t->tm_mon+1, t->tm_mday, t->tm_hour, t->tm_min);
128 }
129
130 void link_printf(const char* filename)
131 {
132 char buf[1024] = "123";
133 if(0 == readlink(filename, buf, sizeof(buf)))
134 error_printf("readlink");
135 printf("-> %s ",buf);
136 }
3. main_myls.c
1 #include "myls.h"
2
3
4 int main(const char argc, const char** argv)
5 {
6 char path[1024] = {};
7
8 if(argc == 2 && !(strcmp(argv[1],"-l"))) // 判断命令格式
9 strcpy(path,"./");
10 else if(argc != 3)
11 {
12 printf("格式有误！ \n");
13 exit(EXIT_FAILURE);
14 }
15 else
16 strcpy(path,argv[2]);
17
18 if(!(strcmp(argv[1],"-l")))
19 {
20 struct stat file_message = {};
21 int ret_stat = stat(path, &file_message);
22
23 if(ret_stat == -1)
24 error_printf("stat");
25
26 if(S_ISDIR(file_message.st_mode)) // 判断是否为目录
27 list_dir(path);
28 else
29 list_message(path, &file_message);
30 }
31 else
32 {
33 printf("error in main!\n");
34 exit(EXIT_FAILURE);
35 }
36 return 0;
37 }
原文地址：https://www.cnblogs.com/usingnamespace-caoliu/p/9351773.html
时间： 2024-10-08 08:55:57