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file

The file command is a standard Unix utility used to determine the type of a file. It performs a series of tests on the file to classify it based on its content rather than its name or extension.

How file Works

  1. Magic Number Test: The file command first checks the file's magic number, which is a unique identifier at the beginning of the file. This helps identify the file type.

  2. File System Tests: It performs various file system tests to check for specific file types like directories, symbolic links, and special files.

  3. Text File Tests: If the file is not identified by the previous tests, file checks if it is a text file and tries to determine the character encoding and language.

  4. Default to ASCII: If all tests fail, file defaults to identifying the file as ASCII text.

Key Features

  • Basic Usage: By default, file provides a brief description of the file type.

  • Verbose Output: The -v option provides more detailed information.

  • Follow Symlinks: The -L option follows symbolic links to determine the type of the target file.

  • Magic File: The -m option allows specifying a custom magic file for identifying file types.

Example Usage

# Basic usage file filename # Verbose output file -v filename # Follow symbolic links file -L symlink # Use a custom magic file file -m custom_magic_file filename

Supported Systems

The file command is available on most Unix-like operating systems, including:

  • Linux: Commonly available on various Linux distributions.

  • macOS: Included in macOS by default.

  • FreeBSD: Available as part of the base system.

  • NetBSD: Included in the base system.

  • OpenBSD: Part of the base system.

It is not natively available on Windows, but similar functionality can be achieved using third-party tools like Cygwin or Windows Subsystem for Linux (WSL).

Last modified: 19 December 2024
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