Task 2: lsal (40pt.)

One of the most basic and useful packages shipped with all GNU/Linux operating systems is coreutils. It provides you system utilities such as ls and rm. At this point of the semester, you know enough to be able to implement similar functionality by using system calls in C. That is exactly how coreutils is implemented too!

In this task, you will implement a special version of the ls program, called lsal. In particular, you need to write a C program that accepts a command-line argument and behaves almost like ls -al, printing details of all files. The followings will explain the expected behavior:

If an argument is provided, it can be either a file name or a directory name. If the argument is a directory name, you will list all files/directories inside it. Otherwise, you only list the corresponding file.

Note that "." or ".." are directories as well and therefore your program should work for them too.

If an argument is not provided your program will list the working directory (same as ".").

In order to retrieve and inspect the file information, you need to carefully study the inode's manual.

Only list the regular files and directories. Skip other types such as links, etc. See inode for how to test the file type.

Your output must be exactly the same as in ls. Therefore, you can use diff as you have seen in previous test scripts to fully test your program before submission. This is of course true for directories that contain regular files and directories only. For example, your output would not list a symlink while ls does.

Make sure that you also replicate the behavior of ls if file/directory cannot be found by printing the same error message to stderr.

Hint: Some of the system calls that may be useful for this Task include opendir, readdir, lstat, getpwuid, and getgrgid.

Hint: Make sure you pass the full pathname (absolute/relative) as argument to functions such as lstat.

Task 3: Improved lsal (10pt.)

As you know, ls can accept multiple arguments. Improve your code from Task 2 to provide the same flexibility in a new program called lsal2. Note that when multiple arguments are passed to ls, for directories it also prints the name of the directory before listing the files inside it.

Hint: Write your code as modular as possible to avoid duplicating code that might be reused. That way you avoid debugging same errors again and again. For example, you should put any shared functionality between lsal.c and lsal2.c (i.e., most of what Task 2 asks you to do) in a separate source file which will be linked to your lsal.o and lsal2.o code to make the executable files.