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A nice program to list files in a directory. A version of ls.

by

This program uses stat to list all files in a directory and show the same information as ls -hula. This is a very nice example of Linux programming.

my_ls.c
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/*
*  This program is free software: you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  This program is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
 
/********************************************************************
* Description: A version of ls written in c.
* Author: John Cartwright <XXXXXXXXXXXXXXXXXX>
* Created at: Mon Apr  3 10:38:18 AEST 2023
* Computer: localhost.localdomain
* System: Linux 5.14.0-162.18.1.el9_1.x86_64 on x86_64
*
* Copyright (c) 2023 John Cartwright  All rights reserved.
*
********************************************************************/
 
#include <sys/stat.h>
#include <dirent.h>
#include <string.h>
#include <limits.h>
#include <stdio.h>
#include <time.h>
#include <pwd.h>
#include <grp.h>
 
#define syscall(a, D, S, d) __asm__ __volatile__("syscall" : : "a"(a), "D"(D), "S"(S), "d"(d))
 
void list_files(const char *path) {
 
    struct dirent *entry;
    struct stat file_stat;
    char full_path[PATH_MAX];
 
    DIR *dir = opendir(path);
 
    if (dir == NULL) {
        perror("opendir");
        return;
    }
 
    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") == 0) {
            continue;
        }
 
        snprintf(full_path, sizeof(full_path), "%s/%s", path, entry->d_name);
 
        if (stat(full_path, &file_stat) < 0) {
            perror("stat");
            continue;
        }
 
        struct passwd *user_info = getpwuid(file_stat.st_uid);
        struct group *group_info = getgrgid(file_stat.st_gid);
 
        printf("%s", S_ISDIR(file_stat.st_mode) ? "d" : "-");
        printf("%s", (file_stat.st_mode & S_IRUSR) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWUSR) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXUSR) ? "x" : "-");
        printf("%s", (file_stat.st_mode & S_IRGRP) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWGRP) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXGRP) ? "x" : "-");
        printf("%s", (file_stat.st_mode & S_IROTH) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWOTH) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXOTH) ? "x" : "-");
 
        printf(" %ld", file_stat.st_nlink); /* Print file hardlinks. */
        printf(" %s ", user_info->pw_name); /* Print file owner username. */
        printf("%s ", group_info->gr_name); /* Print file owner groupname. */
 
            if (file_stat.st_size > 1000000) { /* Checking if we are seeing a
                file that is more than one Megabyte. */
            long file_size_bytes = file_stat.st_size;
            double file_size_mb = (double)file_size_bytes / (1024.0 * 1024.0);
            printf(" %.2f MB ", file_size_mb);
            }
            else if (file_stat.st_size > 1000) { /* Checking if we are seeing a
                file that is more than one Kilobyte. */
            long file_size_bytes = file_stat.st_size;
            double file_size_kb = (double)file_size_bytes / 1024.0;
            printf(" %.2f KB ", file_size_kb);
            } else {
                /* Otherwise, the filesize is in bytes and we just print this.
                 * Not too hard.
                */
                printf(" %ld bytes", file_stat.st_size);
            }
        printf(" %ld", file_stat.st_mtime);
        printf(" %s\n", entry->d_name);
    }
 
    closedir(dir);
}
 
int main(int argc, char *argv[]) {
 
    if (argc == 1) {
        list_files(".");
    } else {
        printf("%s", argv[1]);
        list_files(argv[1]);
    }
 
    syscall(1, 1, "End of listing.\n", 16);
    syscall(60, 0, 0, 0);
 
    return 0;
}

This shows the username and group of the file owner, and the filesize as well. Below is the output this program will give you.

(jcartwright@localhost) 192.168.1.5 Documents  $ ./myls
drwx--x--- 20 jcartwright jcartwright  4.00 KB  1690830117 ..
drwxr-xr-x 2 jcartwright jcartwright  41 bytes 1690498197 html
-rw-r--r-- 1 jcartwright jcartwright  526 bytes 1688428947 vid.py
-rw-r--r-- 1 jcartwright jcartwright  20.58 MB  1688508774 9rbtxh.pdf
-rw-r--r-- 1 jcartwright jcartwright  980 bytes 1688684231 ipv6.asm
-rw-r--r-- 1 jcartwright jcartwright  1.39 KB  1688684236 ipv6.o
-rwxr-xr-x 1 jcartwright jcartwright  8.31 KB  1688684238 ipv6
-rw-r--r-- 1 jcartwright jcartwright  194 bytes 1688942844 colors.sh
drwxr-xr-x 10 jcartwright jcartwright  4.00 KB  1689120655 rtl-sdr
-rw-r--r-- 1 jcartwright jcartwright  177 bytes 1689215012 y.c
-rwxr-xr-x 1 jcartwright jcartwright  25.23 KB  1689215016 y
-rw-r--r-- 1 jcartwright jcartwright  145.71 KB  1689368699 mpv-shot0001.jpg
-rw-r--r-- 1 jcartwright jcartwright  113.08 KB  1689368707 mpv-shot0002.jpg
-rw-r--r-- 1 jcartwright jcartwright  3.89 KB  1689816153 images.c
-rwxr-xr-x 1 jcartwright jcartwright  26.30 KB  1689816160 system_info
-rwxr-xr-x 1 jcartwright jcartwright  205 bytes 1689896400 xp.sh
-rw-r--r-- 1 jcartwright jcartwright  4.00 KB  1690839106 myls.c
-rw-r--r-- 1 jcartwright jcartwright  2.07 KB  1690240175 xlogo.c
-rw-r--r-- 1 jcartwright jcartwright  2.65 KB  1349779195 xterm-color_48x48.xpm
-rw-r--r-- 1 jcartwright jcartwright  2.52 KB  1349650602 xterm_48x48.xpm
-rw-r--r-- 1 jcartwright jcartwright  2.07 KB  1690240294 png.c
-rwxr-xr-x 1 jcartwright jcartwright  26.11 KB  1690240297 xorg_logo
drwxr-xr-x 5 jcartwright jcartwright  4.00 KB  1684566812 wordpress
drwxr-xr-x 12 jcartwright jcartwright  4.00 KB  1587781946 eureka-1.27b-source
-rwxr-xr-x 1 jcartwright jcartwright  25.75 KB  1690692736 lsme
drwxr-xr-x 14 jcartwright jcartwright  4.00 KB  1690747190 yadex
drwxrwxrwx 14 jcartwright jcartwright  24.00 KB  1690680931 fuck
-rwxr-xr-x 1 jcartwright jcartwright  25.70 KB  1690839139 myls
End of listing.

This might be very useful as an example of programming using <sys/stat.h>.

I could also create a file myls.h and include the void function and other stuff in there.

myls.h
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#define syscall(a, D, S, d) __asm__ __volatile__("syscall" : : "a"(a), "D"(D), "S"(S), "d"(d))
 
void list_files(const char *path) {
 
    struct dirent *entry;
    struct stat file_stat;
    char full_path[PATH_MAX];
 
    DIR *dir = opendir(path);
 
    if (dir == NULL) {
        perror("opendir");
        return;
    }
 
    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") == 0) {
            continue;
        }
 
        snprintf(full_path, sizeof(full_path), "%s/%s", path, entry->d_name);
 
        if (stat(full_path, &file_stat) < 0) {
            perror("stat");
            continue;
        }
 
        struct passwd *user_info = getpwuid(file_stat.st_uid);
        struct group *group_info = getgrgid(file_stat.st_gid);
 
        printf("%s", S_ISDIR(file_stat.st_mode) ? "d" : "-");
        printf("%s", (file_stat.st_mode & S_IRUSR) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWUSR) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXUSR) ? "x" : "-");
        printf("%s", (file_stat.st_mode & S_IRGRP) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWGRP) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXGRP) ? "x" : "-");
        printf("%s", (file_stat.st_mode & S_IROTH) ? "r" : "-");
        printf("%s", (file_stat.st_mode & S_IWOTH) ? "w" : "-");
        printf("%s", (file_stat.st_mode & S_IXOTH) ? "x" : "-");
 
        printf(" %ld", file_stat.st_nlink); /* Print file hardlinks. */
        printf(" %s ", user_info->pw_name); /* Print file owner username. */
        printf("%s ", group_info->gr_name); /* Print file owner groupname. */
 
            if (file_stat.st_size > 1000000) { /* Checking if we are seeing a
                file that is more than one Megabyte. */
            long file_size_bytes = file_stat.st_size;
            double file_size_mb = (double)file_size_bytes / (1024.0 * 1024.0);
            printf(" %.2f MB ", file_size_mb);
            }
            else if (file_stat.st_size > 1000) { /* Checking if we are seeing a
                file that is more than one Kilobyte. */
            long file_size_bytes = file_stat.st_size;
            double file_size_kb = (double)file_size_bytes / 1024.0;
            printf(" %.2f KB ", file_size_kb);
            } else {
                /* Otherwise, the filesize is in bytes and we just print this.
                 * Not too hard.
                */
                printf(" %ld bytes", file_stat.st_size);
            }
        printf(" %ld", file_stat.st_mtime);
        printf(" %s\n", entry->d_name);
    }
 
    closedir(dir);
}

Once that is done, the main source file is cleaner.

myls.c
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/*
*  This program is free software: you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  This program is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
 
/********************************************************************
* Description: A version of ls written in c.
* Author: John Cartwright <[email protected]>
* Created at: Mon Apr  3 10:38:18 AEST 2023
* Computer: localhost.localdomain
* System: Linux 5.14.0-162.18.1.el9_1.x86_64 on x86_64
*
* Copyright (c) 2023 John Cartwright  All rights reserved.
*
********************************************************************/
 
#include <sys/stat.h>
#include <dirent.h>
#include <string.h>
#include <limits.h>
#include <stdio.h>
#include <time.h>
#include <pwd.h>
#include <grp.h>
 
#include "myls.h"
 
int main(int argc, char *argv[]) {
 
    if (argc == 1) {
        list_files(".");
    } else {
        printf("%s", argv[1]);
        list_files(argv[1]);
    }
 
    syscall(1, 1, "End of listing.\n", 16);
    syscall(60, 0, 0, 0);
 
    return 0;
}

This program even compiles and runs on a Macintosh PC. This is amazing. But it is a very simple program.

(04:07 pm)Documents $> ./myls stuff/
stuff/drwx------ 79 jason staff  2.47 KB  1690870016 ..
-rw-r--r-- 1 jason staff  385.37 KB  1546599903 mardi-gras-2016-fuse-magazine.jpg
-rw-r--r-- 1 jason staff  51.30 KB  1514880390 93bffab7a44bc518799a2a68711ad790.jpg
-rw-r--r-- 1 jason staff  335.34 KB  1539597643 1538995576940.png
-rwxrwxrwx 1 jason staff  156.05 KB  1503489616 wifi-crack.png
-rw-r--r-- 1 jason staff  0.96 MB  1547547050 1514877771595.jpg
-rw-r--r-- 1 jason staff  48.23 KB  1545638172 8c9ec9b3d45be9f9c880e850861a5fc7.jpg
-rw-r--r-- 1 jason staff  1.88 MB  1547548193 images.tar.bz2

C code is very portable.

(04:07 pm)Documents $> file myls
myls: Mach-O 64-bit executable x86_64
()deusexmachina.local-_

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