OPS102 W2C1: File Systems and Folders

File Systems

• A file system is a method of organizing and retrieving files efficiently from a storage medium, e.g., a hard disk.
• Both Linux and Windows use hierarchical file systems, where files are organized in folders and subfolders.
• The original (pre-GUI) name for folders is "directories".
• In Windows File System, the hierarchy starts from drives: C, D, etc.
• There are no drive letters like C, or D in Linux.
• In Linux, the topmost directory is the root (/), and all files and directories appear under root.
• Windows has a per-drive root directory, e.g., D:.

Files and Folders (Directories)

• Virtually everything in a modern computer system is a file or a folder.
• Folders are containers that can have files and other folders (called sub-folders).
• Files are used to save user data (or any data) and can be of many different types, e.g., Word DOC document file, C programming language source file, compiled object code file, SQLite database file.
• File types are identified from their extensions – the 3 or 4 last characters after a period/dot.
• Examples of file extensions: .docx – Microsoft Word documents, .exe – an executable program on Windows, .txt – a text file.

Paths: Absolute, Relative, Relative to Home

• A path specifies a unique location of a file or directory in the file system.
• The file system location is found by following the directory tree hierarchy.
• A path is written as a string of characters in which directories are separated by the path separator: a forward slash “/” in Linux and MacOS, or a backslash “\” in Windows.
• There are multiple ways of specifying pathnames: Absolute pathnames, Relative pathnames, Relative to home pathnames.
• Examples of absolute pathnames: /home/jones/Desktop/paris.jpg, D:\Trips\Paris\Louvre.
• Relative pathname: A pathname that does not start with a slash is a relative pathname, and is interpreted relative to the current directory.
• Example of a relative pathname: The argument to cat is relative to CWD: [jane@machine: /home/jane/Documents/]$ cat ./Math/marks.txt.
• Relative to home pathname – on Linux/Unix, a tilde (“∼”) is used as a shorthand for the user’s home directory.
• Example: from anywhere show the contents in Documents folder: [jane@machine: /var/log/]$ ls ~/Documents/.

Current Working Directory

• The current working directory is the folder/directory where you are working at a given time.
• If you are viewing Documents folder in file explorer, then Documents is your current working directory.
• The current working directory is a more important concept when you are interacting with your system through a command-line interface.
• Whenever a user opens a terminal, their home directory is their current working directory.
• We can navigate in the file system and change our current working directory any time using the cd (change directory) command (Linux and Windows).

Changing the Current Working Directory

• In a command-line interface (CLI), we use the command cd to change our current working directory.
• The argument can be any type of path (absolute, relative, or relative to home).
• Examples of cd in Linux: cd /bin, change directory to "/bin", cd, change directory to your home directory, cd ~, change directory to your home directory, cd .., change to parent directory.
• Examples of cd in Windows: cd D:\Courses\OPS102, change directory to "D:\Courses\OPS102", cd, display current directory, cd .., change to parent directory.

File and Folder Names

• Unix/Linux is case sensitive!
• Windows is not case sensitive for file names.
• Adopt a consistent file naming scheme – this will help you find your files later.
• Make your file and folder/directory names meaningful.
• Avoid non-alphanumeric characters, as they may have a special meaning to the system that will make your work more difficult.
• Avoid using spaces in file names – consider periods, hyphens, and underscores instead, spaces in file names can lead to inconsistent results while working in the command-line interface.