本文利用以下系統呼叫實現ls -l命令的功能：
1，lstat：獲得檔案狀態,
2，getpwuid：
#include <pwd.h>
struct passwd *getpwuid(uid_t uid);
描述：
The getpwuid() function returns a pointer to a structure containing the broken-out fields of the record in the password database that matches the user ID uid.
返回值：
The passwd structure is defined in <pwd.h> as follows:
struct passwd {
char *pw_name; /* username */
char *pw_passwd; /* user password */
uid_t pw_uid; /* user ID */
gid_t pw_gid; /* group ID */
char *pw_gecos; /* real name */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};
示例：
#include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <pwd.h> #define ERR_EXIT(m) \ do \ { \ perror(m); \ exit(EXIT_FAILURE); \ } while(0) int main(void) { uid_t uid; struct passwd *pw; uid = getuid(); printf("current user id :%d\n",uid); if((pw = getpwuid(uid)) == NULL) ERR_EXIT("getpwuid error"); printf("username:%s\n",pw->pw_name); printf("user passwd:%s\n",pw->pw_passwd); printf("user ID:%d\n",pw->pw_uid); printf("group ID:%d\n",pw->pw_gid); //printf("real name:%s\n",pw->pw_gecos); printf("home directory:%s\n",pw->pw_dir); printf("shell program:%s\n",pw->pw_shell); return 0; }
執行結果：
3，getgrgid:
#include <grp.h>
struct group *getgrnam(const char *name);//根據組名獲得組資訊
struct group *getgrgid(gid_t gid);//根據組ID獲得組資訊
描述：
The getgrnam() function returns a pointer to a structure containing the broken-out fields of the record in the group database (e.g., the local group file /etc/group, NIS, and LDAP) that matches the group name name.
The getgrgid() function returns a pointer to a structure containing the broken-out fields of the record in the group database that matches thegroup ID gid.
返回值：
The group structure is defined in <grp.h> as follows:
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group ID */
char **gr_mem; /* group members */
};
4，readlink:讀取軟連結檔案的內容
#include <unistd.h>
ssize_t readlink(const char *path, char *buf, size_t bufsiz);
描述：
DESCRIPTION
readlink() places the contents of the symbolic link path in the buffer
buf, which has size bufsiz. readlink() does not append a null byte to
buf. It will truncate the contents (to a length of bufsiz characters),
in case the buffer is too small to hold all of the contents.
RETURN VALUE
On success, readlink() returns the number of bytes placed in buf. On
error, -1 is returned and errno is set to indicate the error.
示例：
#include <unistd.h> #include <stdlib.h> #include <stdio.h> #define ERR_EXIT(m) \ do \ { \ perror(m); \ exit(EXIT_FAILURE); \ } while(0) int main(int argc,char **argv) { if(argc != 2){ fprintf(stderr,"usage:%s linkfile", argv[0]); exit(EXIT_FAILURE); } char buf[1024]; if(readlink(argv[1],buf,1024) ==-1) ERR_EXIT("readlink error"); printf("the content of %s are: %s\n",argv[1],buf); return 0; }
執行結果：
現在利用相關的系統呼叫實現ls –l功能：
程式如下：
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <dirent.h> #include <sys/types.h> #include <sys/stat.h> #include <string.h> #include <time.h> #include <pwd.h> #include <grp.h> #include <libgen.h> #define ERR_EXIT(m) \ do\ {\ perror(m);\ exit(EXIT_FAILURE);\ }while(0)\ void lsdir(char *dirname); void lsfile(char *filename); void lsfile(char *filename); char getFileType(struct stat *fstat); void getFilePerm(struct stat *st, char *perm); int main(int argc,char **argv) { if(argc != 2){ fprintf(stderr,"usage:%s [filepath]\n",argv[0]); exit(EXIT_FAILURE); } struct stat fstat; if(lstat(argv[1],&fstat) == -1) ERR_EXIT("STAT ERROR"); if(S_ISDIR(fstat.st_mode)) { lsdir(argv[1]); } else{ lsfile(argv[1]); } return 0; } void lsdir(char *dirname) { DIR *dir; char filename[100] = {0}; dir =opendir(dirname); if(dir == NULL) ERR_EXIT("opendir error"); struct dirent *dentry; while((dentry = readdir(dir)) != NULL) { char *fname; fname = dentry->d_name; if(strncmp(fname,".",1) == 0) continue; sprintf(filename,"%s/%s",dirname,fname); lsfile(filename); } closedir(dir); } //-rw-r--r--. 1 zxy zxy 2586 Jul 10 17:00 ls.c //型別及許可權 硬連結數 擁有者 所屬組 檔案大小 建立時間 檔名 void lsfile(char *filename) { struct stat tmpstat; if(lstat(filename,&tmpstat) == -1) ERR_EXIT("STAT ERROR"); char buf[11]= {0}; strcpy(buf,"----------"); char type; type = getFileType(&tmpstat); char *bname = basename(filename); buf[0] = type; if(type == 'l'){ char content[1024]; if(readlink(filename,content,1024) == -1) ERR_EXIT("readlink error"); sprintf(bname,"%s -> %s",bname,content); } getFilePerm(&tmpstat,buf); struct tm *ftime; ftime = localtime(&tmpstat.st_mtime); printf("%s %d %s %s %10ld %02d %02d %02d:%02d %s\n", buf,tmpstat.st_nlink, getpwuid(tmpstat.st_uid)->pw_name, getgrgid(tmpstat.st_gid)->gr_name, tmpstat.st_size, ftime->tm_mon+1, ftime->tm_mday, ftime->tm_hour, ftime->tm_min, bname); } //獲得檔案型別 char getFileType(struct stat *st) { char type = '-'; switch (st->st_mode & S_IFMT) { case S_IFSOCK: type = 's'; break; case S_IFLNK: type = 'l'; break; case S_IFREG: type = '-'; break; case S_IFBLK: type = 'b'; break; case S_IFDIR: type = 'd'; break; case S_IFCHR: type = 'c'; break; case S_IFIFO: type = 'p'; break; } return type; } //獲得檔案訪問許可權 void getFilePerm(struct stat *st, char *perm) { mode_t mode = st->st_mode; if (mode & S_IRUSR) perm[1] = 'r'; if (mode & S_IWUSR) perm[2] = 'w'; if (mode & S_IXUSR) perm[3] = 'x'; if (mode & S_IRGRP) perm[4] = 'r'; if (mode & S_IWGRP) perm[5] = 'w'; if (mode & S_IXGRP) perm[6] = 'x'; if (mode & S_IROTH) perm[7] = 'r'; if (mode & S_IWOTH) perm[8] = 'w'; if (mode & S_IXOTH) perm[9] = 'x'; }
執行結果：
