ls.c

#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <fcntl.h>
#include <errno.h>
#include <memory.h>
#include <linux/limits.h>
#include <sys/wait.h>

void fill_attrs(char* attrs, mode_t mode) {

    if (S_ISDIR(mode)) {
        attrs[0] = 'd';
    }

    if (S_IRUSR & mode) {
        attrs[1] = 'r';
    }
    if (S_IWUSR & mode) {
        attrs[2] = 'w';
    }
    if (S_IXUSR & mode) {
        attrs[3] = 'x';
    }
    if (S_IRGRP & mode) {
        attrs[4] = 'r';
    }
    if (S_IWGRP & mode) {
        attrs[5] = 'w';
    }
    if (S_IXGRP & mode) {
        attrs[6] = 'x';
    }
    if (S_IROTH & mode) {
        attrs[7] = 'r';
    }
    if (S_IWOTH & mode) {
        attrs[8] = 'w';
    }
    if (S_IXOTH & mode) {
        attrs[9] = 'x';
    }
}

void processDir(const char* d) {
    DIR* dir = NULL;

    chdir(d);
    dir = opendir("./");

    /*
    char newdir[PATH_MAX];    
    strcpy(newdir, "./");
    strcat(newdir, d);
    dir = opendir(newdir);    

    printf("\npid %d, dir %s\n", getpid(), newdir);
    */

    
    if (dir == NULL) {
        printf("Cannot open directory %s, err: %d\n", d, errno);
        return;
    }

    struct dirent* ent = NULL;
    struct stat st;
    char attrs[11]; // drwxrwxrwx
    while ((ent = readdir(dir)) != NULL) {        
        strcpy(attrs, "----------");
        lstat(ent->d_name, &st);
        fill_attrs(attrs, st.st_mode);

        printf("%s %10ld %s", attrs, st.st_size, ent->d_name);

        if (S_ISLNK(st.st_mode)) {
            char buf[PATH_MAX + 1];
            readlink(ent->d_name, buf, PATH_MAX + 1);

            struct stat st1;
            if (stat(buf, &st1) == -1) {
                printf("                        symlink broken");            
            } else {
                printf("                        symlink");
            }            
        }

        if ((S_ISDIR(st.st_mode) != 0) && 
                (strncmp(ent->d_name, ".", 1) != 0) &&
                (strncmp(ent->d_name, "..", 2) != 0)) {
                if (fork() == 0) {
                    // child
                    processDir(ent->d_name);
                    break;
                } else {
                    //printf("\nDir: %s\n", ent->d_name);
                    int status;
                    wait(&status);
                    //break;
                }

            }

        printf("\n");
    }
}

int main(int argc, char const *argv[]) {
    printf("My pid %d\n", getpid());

    if (argc > 1) {
        processDir(argv[1]);
    } else {
        processDir(".");        
    }

    printf("\n\n\n\n\n");    
    
    return 0;
}