《unix/linux编程实践教程》学习笔记：第三章 编写ls

概念准备
目录是一种特殊的文件，它的内容是文件和目录的名字，每一个目录都包括两个特殊的项——“.”（当前目录文件列表）和“..”（上一级目录文件列表）。可以通过命令显示隐藏的文件

ls -a

显示出来，也可以通过vim .打开目录文件。

编写ls的思路就是读取.文件，通过printf打印。

如何读取目录的内容?
学习三个系统调用：opendir，readdir,closedir

编写ls

#include <stdio.h>#include <sys/types.h>#include <dirent.h>void do_ls(char []);int main(int ac,char *av[]){    if(ac == 1)        do_ls(".");    else       while(-- ac){        printf("%s:\n",*++av);        do_ls(*av);       }    return 0;}void do_ls(char dirname[]){    DIR * dir_ptr;    struct dirent * direntp;    if((dir_ptr = opendir(dirname)) == NULL)        fprintf(stderr,"lsl:cannot open %s\n",dirname);    else    {        while((direntp = readdir(dir_ptr)) != NULL)            printf("%s\n",direntp -> d_name);        closedir(dir_ptr);    }}

编写ls -l
（1）ls - l 可以查看文件的属性和信息，要实现它的功能，我们需要学习系统调用stat
stat使用例子

#include <stdio.h>#include <sys/types.h>#include <sys/stat.h>int main(int ac, char *av[]){    struct stat info;    if(ac > 1)            if( stat(av[1],&info) != -1){                show_stat_info(av[1],&info);                return 0;            }else{                perror(av[1]);            }    return 1;}show_stat_info(char *fname, struct stat *buf){    printf("    mode: %o\n",buf->st_mode);    printf("   links: %d\n",buf->st_nlink);    printf("    user: %d\n",buf->st_uid);    printf("   group: %d\n",buf->st_gid);    printf("    size: %d\n",buf->st_size);    printf(" modtime: %d\n",buf->st_mtime);    printf("    name: %s\n",fname);}

（2）模式字段转换为字符
使用掩码解码,例如：
if(mode & S_IRUSR) str[1] = ‘r’;.

#include <stdio.h>#include <sys/types.h>#include <sys/stat.h>#include <dirent.h>#include <string.h>void do_ls(char []);void dostat(char *);void show_file_info(char *,struct stat *);void mode_to_letters(int,char []);char *uid_to_name(uid_t);char *gid_to_name(gid_t);int main(int ac,char *av[]){    if(ac == 1)        do_ls(".");    else       while(-- ac){        printf("%s:\n",*++av);        do_ls(*av);       }    return 0;}void do_ls(char dirname[]){    DIR * dir_ptr;    struct dirent * direntp;    if((dir_ptr = opendir(dirname)) == NULL)        fprintf(stderr,"lsl:cannot open %s\n",dirname);    else    {        while((direntp = readdir(dir_ptr)) != NULL)            dostat(direntp->d_name);        closedir(dir_ptr);    }}void dostat(char *filename){    struct stat info;    if(stat(filename,&info) == -1)        perror(filename);    else        show_file_info(filename,&info);}void show_file_info(char * filename,struct stat * info_p){    char *uid_to_name(),*ctime(),*gid_to_name(),*filemode();    void mode_to_letters();    char modestr[11];    mode_to_letters(info_p->st_mode,modestr);    printf("%s",modestr);    printf("%4d",(int)info_p->st_nlink);    printf("%-5s",uid_to_name(info_p->st_uid));    printf("%-5s",gid_to_name(info_p->st_gid));    printf("%5ld ",(long)info_p->st_size);    printf("%.10s ",4+ctime(&info_p->st_mtime));    printf("%s\n",filename);}void mode_to_letters(int mode,char str[]){    strcpy(str,"------------");    if(S_ISDIR(mode)) str[0] = 'd';    if(S_ISCHR(mode)) str[0] = 'c';    if(S_ISBLK(mode)) str[0] = 'b';    if(mode & S_IRUSR) str[1] = 'r';    if(mode & S_IWUSR) str[2] = 'w';    if(mode & S_IXUSR) str[3] = 'x';    if(mode & S_IRGRP) str[4] = 'r';    if(mode & S_IWGRP) str[5] = 'w';    if(mode & S_IXGRP) str[6] = 'x';    if(mode & S_IROTH) str[7] = 'r';    if(mode & S_IWOTH) str[8] = 'w';    if(mode & S_IXOTH) str[9] = 'x';}#include <pwd.h>char *uid_to_name( uid_t uid){    struct passwd * getpwuid(), *pw_ptr;    static char numstr[10];    if((pw_ptr = getpwuid(uid)) == NULL){     sprintf(numstr,"%d",uid);     return numstr;    }    else      return pw_ptr->pw_name;}#include <grp.h>char *gid_to_name(gid_t gid){    struct group *getgrpid(),*grp_ptr;    static char numstr[10];    if((grp_ptr = getgrgid(gid)) == NULL){      sprintf(numstr,"%d",gid);      return numstr;    }    else        return grp_ptr->gr_name;}

设置和修改文件属性
chmod:修改文件的许可权限和特殊属性
chown:修改文件所有者和组
utime:修改文件的最后访问时间和最后修改时间
rename：修改文件名或移动文件的位置