CS456 - Systems Programming Spring 2025

Displaying ./code/ls/ls_simple.c

/*

an extremely simplified version of the ls command,

it works, but a lot of stuff is missing, and there are bugs where 
segmentation faults will result. see notes below the main function

*/

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


int main(int argc, char **argv){

	DIR *mydir;          //defining a pointer to a directory
	struct dirent *file; //accessing the dirent struct, defined in dirent.h
	char filename[512];  //buffer for filename

	//have it print the current directory, if no filename given,
	// otherwise print the directory specified
	if(argc < 2)
		strcpy(filename, ".");
	else
		strcpy(filename, argv[1]);


	mydir = opendir(filename);

	// then we will run through the directory, printing the directory contents
	while((file = readdir(mydir)) != NULL){
		printf("%s\n", file->d_name);
	}
	
	//we're done, so close the directory
	closedir(mydir);

	return 0;

}

/*

THINGS TO DO TO IMPROVE THIS
1. if no directory is specified, just print the current directory - Done
2. if specified file isn't a directory, say so
3. handle arguments given at the command line, 
	- like -l and -a, 
	- or both at the same time 
	- or neither

Things to know/learn:
- how ls -l is structured (from left to right):
	- file type
	- permissions
	- number of links / directories inside the directory
	- the group this file belongs to
	- size in bytes
	- date last modified
	- the file name

- how to tell if something is a directory or not (what function can we use?)

- how to tell our program that the argument is an option, and this argument is our file

- should already be familiar with the stat struct
- the dirent struct and dirent.h header
- there are also structs that store user and group information 
	- passwd struct, defined in pwd.h
	- group struct, defined in grp.h
-may want to know how to know how ctime function works as well

*/