ls.c

#include <stdio.h>
#include <dirent.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <stdlib.h>

#define sz 100

int main(int argc, char **argv)
{
	char *flag = argv[1], *args = argv[2];
	
	struct stat file_stat;
	struct dirent *entry;
	DIR *dir;
	
	if (strlen(args) == 0)				//ls 
		dir = opendir(".");
	else 								//ls path_name
		dir = opendir(args);
		
	if (dir == NULL){
		dir = opendir(".");
		while ((entry = readdir(dir))) {
			if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
				continue;
			if (strcmp(entry->d_name, args) == 0) {
				printf("%s\n", args);
				return 0;
			}
		}
		printf("%s\n", "No such directory");
		return 0;
	}

	if (strlen(flag) > 1) {
		printf("\n%s\n", "Error: Invalid flag!");
		return 0;
	}
	
	if (strlen(flag) == 0) {
		while ((entry = readdir(dir))) {
			if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
				continue;
			printf("%s\n", entry->d_name);
		}
		printf("\n");
		return 0;
	}
	
	else {
		if (flag[0] == 'a') {
			while ((entry = readdir(dir))) {
				printf("%s\n", entry->d_name);
			}
			printf("\n");
		}
		else if (flag[0] == 'l') {
			while ((entry = readdir(dir))) {
				if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
					continue;
				
				char * temp = (char*)malloc(200 * sizeof(char));
				if (strlen(args) != 0)
					strcpy(temp, args);
				else
					strcpy(temp, ".");

				strcat(temp, "/");
				strcat(temp, entry->d_name);

				int check = stat(temp, &file_stat);

				if (check == -1) {
					perror("Error");
					return 0;
				}

				printf((S_ISDIR(file_stat.st_mode)) ? "d" : "-");
				printf((file_stat.st_mode & S_IRUSR) ? "r" : "-");
				printf((file_stat.st_mode & S_IWUSR) ? "w" : "-");
				printf((file_stat.st_mode & S_IXUSR) ? "x" : "-");
				printf((file_stat.st_mode & S_IRGRP) ? "r" : "-");
				printf((file_stat.st_mode & S_IWGRP) ? "w" : "-");
				printf((file_stat.st_mode & S_IXGRP) ? "x" : "-");
				printf((file_stat.st_mode & S_IROTH) ? "r" : "-");
				printf((file_stat.st_mode & S_IWOTH) ? "w" : "-");
				printf((file_stat.st_mode & S_IXOTH) ? "x" : "-");
				printf(" ");
				printf(" %d ", file_stat.st_uid);
				printf(" %d ", file_stat.st_gid);
				printf(" %ld ", file_stat.st_size);
				
				char str[32];
				strftime(str, sizeof(str), "%c", localtime(&file_stat.st_atime));
				printf(" %s ", str);
				printf("%s\n", entry->d_name);
			}
		}
		
		else {
			printf("%s", "Error: Invalid flag!");
		}
		
		return 0;
	}

	return 0;
}