GUI Representation of Files

GUI representation involves file browsers, filename extensions, media types, and magic bytes.
Directories are represented as folders within a file browser window, nested to form a tree structure.
Graphical file browsers allow navigation, opening, and inspecting files.

Examples include Windows Explorer (Microsoft Windows), file explorers in macOS, and GUI tools in Linux desktop environments.
Users can select files, double-clicking to open them. Directories can be navigated by double-clicking.
A sidebar often displays commonly used directories and the file system hierarchy.
Mobile systems (phones) often hide file access but still use traditional file systems underneath (e.g., Android, iOS).

Some files have extensions (e.g., .txt), while others do not.
In early DOS, filenames had a maximum of eight characters, followed by a dot and a three-character extension.
Extensions indicate the file type but are not technically required by file systems.
The command line interface (CLI) does not rely on extensions.
Extensions provide an immediate indication of the expected file content.
Extensions are mostly connected to desktop environments.
The desktop environment associates file types with applications based on extensions.

.pdf: Portable Document Format files
.txt: Text files (potentially unformatted)
.png: Portable Network Graphics format (image files)
.jpeg: Another image file format
.docx: Microsoft Word extension (XML files zipped into one file)
.java: Java source code files
.html: Text files formatted with HTML markup language
Standardization of file extensions is incomplete across operating systems.
Desktop environments automatically open files with default applications based on extensions, which can be changed by the user.

Media types offer an alternative to file extensions for indicating file content, especially useful for network traffic.
Developed for sending binary data via email (MIME typing) and quickly adopted by the World Wide Web.
When sending a file, its media type is sent along, indicating how the receiving machine should handle it.
Each OS or application maps file extensions to media types.
Media types are encoded as type/subtype.

Magic bytes predate file extensions and are used to identify file content by examining specific bytes within the file.
Applications often check magic bytes to validate file types, even with extensions or media types, ensuring the file is valid for the application.
Magic bytes are typically located at the start of binary files for quick validation.

FLAC audio files have magic bytes fLaC.
MPEG-4 video files and MP3 files also have associated magic bytes.
Files can have incorrect extensions (e.g., a .txt file containing a PDF document).
PDF readers check for magic bytes to identify and open PDF documents, regardless of the extension.
Relying solely on extensions is not considered good practice.

The file utility determines file content based on magic bytes and other tests.

The man file command provides detailed information on the tool and its tests.
Additional references are available for further reading on file types and handling.