42_ft_ls: Unix-like command to list computer files

Purpose of the project is to recode ls(1).

Project file: ft_ls

Allowed C functions: opendir(3), readdir(3), closedir(3), getpwuid(3), getgrgid(3), time(3), ctime(3), malloc(3), free(3), perror(3), strerror(3), exit(3).

Justifiable C functions for bonus part: tcgetattr(3). Structs found in man 4 tty.

Allowed System Calls: write(2), stat(2)(struct), lstat(2)(struct), listxattr(2), getxattr(2), readlink(2)

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Table of Contents - Click a section to jump to it

• Cloning Repository
• Installing ft_ls macOS only
• ft_ls Usage
• Program Installation Demo
• Program Usage Demo
• Project Summary
  • Parsing
  • -R - Recursively List Subdirectories
  • -L - Long File Listing
  • -t, -r - Sort Files
  • -G - Colorize Output
  • -a - Output Hidden Files and Directories
• Resources and References

Cloning Repository

https://github.com/mohammadbutt/42_ft_ls.git

Installing ft_ls macOS only

make

ft_ls Usage

./ft_ls [-GRalrt] [file ...]

./ft_ls -G
./ft_ls -R
./ft_ls -a
./ft_ls -l
./ft_ls -r
./ft_ls -t

Program Installation Demo

Yup! This is all you need to do to install the program! Scroll down for usage.

Demo

Basic usage

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Colorize directories and executables

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Sort by alphabetical and reverse alphabetical order

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Sort by latest and earliest time file modified

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Project Summary

Parsing - Source Code

When the user runs the program and there in only one argument that is ./ft_ls then the program calls onto the function void single_argument(t_ls *ls, t_info *info, char *dir_path_str). Single_argument calls onto opendir(3), opendir takes in the path of a directory. If a directory has permission denied, then the program will print the name of the directory and then display "permission denied". If a directory is valid, then readdir(3) is used with dirent struct to open the directory and read the contents of the directory one at a time, the contents of the directory are stored in a linked list. A slash is appended after the directory path and the file name is concatenated after it. For example, "this_is_a_directory/file_name". List is saved with the last index of the file. This slash index is used later to print just the file name instead of printing the file path and the name when only the file name is needed.

If there is a dash - after ./ft_ls that's when the program starts collecting flags that are l, R, a, t, r. If there is no dash then the program looks for either a valid or invalid file name, or a directory. If a file name is valid then the program displays the file name, if an entered file does not exist then the program displays a message, "./ft_ls: name_of_invalid_file: No such file or directory", just like the original ls. If the entered name is a directory then the program displays files of that directory.

-R - Recursively list subdirectories - Source Code

If there are two arguments and the R flag exists in the argument then the program recursively enters through directories and subdirectories the open each directory, store the files in a linked list, sorts them, prints the files, frees the linked list, and then moves to the next directory to perform the same action until it gets to the end cant find any more directories to treverse through. This is one of the prime reasons why a directory path and slash is appended right before each file name because. Because in order traverser through and go inside each sub directory it is important to have the path of the parent directory. Below is a rough representation of recursive tree structure:

|___CODEOWNERS
|___Makefile
|___README.md
|___author
|___ft_ls_src
|  |___append_slash.c
|  |___delete_linked_list.c
|  |___ft_printf
|  |  |___Makefile
|  |  |___srcs
|  |  |  |___append_to_buffer.c
|  |  |  |___collect_and_cancel_flags.c
|  |  |  |___mini_libft
|  |  |  |  |___ft_atoi.c
|  |  |  |  |___ft_bzero.c

-l - Long File Listing - Source Code

If there is an l which stands for long listing format, then addtional informatin is printed about each file and directory.

Below is a table and format of ls -l author and ./ft_ls -l author, what each column means.

Permission	Links	owner id	group owner id	size in bytes	month, date, time modified	file name
Permission	st_nlink	st_uid	st_gid	st_size	st_ctimespec.tv_sec	d_name under dirent struct
-rw-r--r--	1	mbutt	2018_october	6	Sep 18 15:35	author

Information for each column is accessible via stat and lstat functions, only file name is retrieved via dirent struct under the member name d_name. Long file listing format is also one of the biggest reasons that file path and a slash is appeneded before each file name because stat and lstat functions need full file path to access the meta data thats shown in the above table. For time modified column, if a file is older than 6 months, then instead of showing the hours and minutes of the file, year of the file is shown instead.

-t, -r - Sort files - Source Code

Files are sorted one of 4 different ways, if there is no -t and -r then files are stored in alphabetical or lexical order. A custom strcmp is used to compare two strings and then merge sort is used to sort the list. If there is -r then files are sorted in reverse alphabetical order. If there is -t then files are sorted by last modified time. Sorting by time also uses merge sort to compare two times in seconds and then merge sorts them. But sorting on time has one addtional step that is if the number of seconds for both files are the same, then nanosecond of both files are also compared. If -tr both t and r are present then files are sorted in reverse time, showing the oldest files first at the top and then showing the newest files at the bottom. ./ft_ls by default just shows the file names, but combining l flag, ./ft_ls -lt or ./ft_ls -ltr would show files sorted by time with time stamp.

-G - Colorize Output - Source Code

When -G is on then the file name is parsed through a function called print_uppercase_g, that takes in the file name with the file path, and stat struct with meta information about the file. If a file is a directory then it is printed in blue. If a file is an executable then it is printed in red. All other file types are printed in the regular font color.

-a - Output Hidden Files and Directories

When -a flag is on, all the files are stored which includes hidden files and directories. Hidden files and directories begin with dot . or dot dot ... Single dot . means current directory. Double dot or dot dot .. means parent directory. If a file has a chacater other than a dot after a single dot, then it's either a hidden file or a directory. Examples would be, .gitignore which is a hidden file, and .git would be a hidden directory.

Resources and References

1. ls - Wikipedia
2. ls source code
3. Decoded ls - maizure.org
4. Simple ls - stackoverflow
5. Members of dirent struct - Apple OS Reference
6. Dirent and Stat usage
7. Differentiate between a unix directory and file in C - Stackoverflow
8. Singly Linked List - Hacker Earth
9. Merge Sort for Linked List - geeksforgeeks
10. C program to list all files in a directory recursively - Codeforwin.org
11. Members of winsize struct - Delorie
12. Members of stat struct - man7.org
13. Members of stat struct st_mode - mkssoftware
14. Recursively list directories in C on Linux - Stackoverflow
15. Carnegie Mellon University - Introduction to Computer Systems - Lecture System Level I/O
16. Big O Cheatsheet - Hackerearth
17. Big O Cheatsheet - bigocheatsheet
18. Algorithms and Data Structures - Cooervo.github.io
19. List all directories in a given directory - Stackoverflow
20. A Recursive Directory Scanning program
21. Linux print file information format
22. View file permissions in Linux
23. ls -l permissions
24. Permission Bits explained
25. Linux File type
26. Determining if a file is a link
27. Extended Attributes @ that appears in permission/chmod