第3章 目录与文件属性：编写ls

/*
 * ls1.c
 * purpose list contents of directory or directories
 * action if no args, use . else list files in args
 */
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>

void do_ls(char []);

main(int ac, char *av[])
{
    if (ac == 1)
        do_ls(".");
    else
        while (--ac) {
            printf("%s:\n", *++av);
            do_ls(*av);
        }
}

void do_ls(char dirname[])
    /*
     * list files in directory called dirname
     */
{
    DIR *dir_ptr;       /* the direcotry */
    struct dirent *direntp; /* each entry */

    if ((dir_ptr = opendir(dirname)) == NULL )
        fprintf(stderr, "ls1:cannot open %s\n", dirname);
    else
    {
        while ((direntp = readdir(dir_ptr)) != NULL)
            printf("%s\n", direntp->d_name);
        closedir(dir_ptr);
    }
}

/*
 * ls2.c
 * purpose list contents of directory or directories
 * action if no args, use . else list files in args
 * note uses stat and pwd.h and grp.h
 * BUG: try ls2 /tmp
 */

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.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);

void main(int ac, char *av[])
{
    if (ac == 1)
        do_ls(".");
    else
        while (--ac) {
            printf("%s:\n", *++av);
            do_ls(*av);
        }
}

void do_ls(char dirname[])
    /*
     * list files in directory called dirname
     */
{
    DIR *dir_ptr;       /* the directory */
    struct dirent *direntp; /* each entry */

    if ((dir_ptr = opendir(dirname)) == NULL)
        fprintf(stderr, "ls1: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)     /* cannot stat */
        perror(filename);       /* say why */
    else                    /* else show info */
        show_file_info(filename, &info);
}

void show_file_info(char *filename, struct stat *info_p)
    /*
     * display the info about filename. The info is stored in struct at *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("%-8s ", uid_to_name(info_p->st_uid));
    printf("%-8s ", gid_to_name(info_p->st_gid));
    printf("%8ld ", (long)info_p->st_size);
    printf("%.12s ", 4 + ctime(&info_p->st_mtime));
    printf("%s\n", filename);
}

/*
 * utility functions
 */
/*
 * This function takes a mode value and a char array
 * and puts into the char array the file type and the
 * nine letters that correspond to the bits in mode.
 * NOTE: It does not code setuid, setgid, and sticky
 * codes
 */
void mode_to_letters(int mode, char str[])
{
    strcpy(str, "----------");      /* default = no perms */

    if (S_ISDIR(mode)) str[0] = 'd';    /* directory? */
    if (S_ISCHR(mode)) str[0] = 'c';    /* char devices */
    if (S_ISBLK(mode)) str[0] = 'b';    /* block devices */

    if (mode & S_IRUSR) str[1] = 'r';   /* 3 bits for user */
    if (mode & S_IWUSR) str[2] = 'w';
    if (mode & S_IXUSR) str[3] = 'x';

    if (mode & S_IRGRP) str[4] = 'r';   /* 3 bits for group */
    if (mode & S_IWGRP) str[5] = 'w';   
    if (mode & S_IXGRP) str[6] = 'x';

    if (mode & S_IROTH) str[7] = 'r';   /* 3 bits for other */
    if (mode & S_IWOTH) str[8] = 'w';
    if (mode & S_IXOTH) str[9] = 'x';
}

#include <pwd.h>
char *uid_to_name(uid_t uid)
    /*
     * returns pointer to username associated with uid, uses getpw()
     */
{
    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)
    /*
     * returns pointer to group number gid. used getgrgid(3)
     */
{
    struct group *getgrgid(), *grp_ptr;
    static char numstr[10];

    if ((grp_ptr = getgrgid(gid)) == NULL) {
        sprintf(numstr, "%d", gid);
        return numstr;
    }
    else
        return grp_ptr->gr_name;
}