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Introduction
The file command in Linux is used to determine the type of a given file. It examines the file content, rather than its extension, to classify the file as a text, executable, archive, image, etc. It is a vital tool for debugging, scripting, and ensuring files are handled correctly in various workflows. file works on virtually all file systems supported by Linux and is a go-to utility for system administrators, developers, and users working with mixed or unknown file types.
The file command is a robust utility that simplifies file type identification in Linux. Its versatility makes it indispensable for troubleshooting, scripting, and daily file management tasks. Share this guide with anyone needing a clear reference to maximize their efficiency with this powerful tool.
Syntax and usage
file [options] <file_name>
Tips for Effective Usage
- Combine with Other Tools: Use file with utilities like
findorxargsto process a large number of files automatically.
find . -type f | xargs file
- Create Reports: Redirect output to a file to generate a report of file types. This is EXTREMELY important if you’re doing filesystem maintenance or working large volumes of data, it’ll help you keep a history of your searches and you can later on parse that history with other tools.
file * > report.txt
- Identify Corrupt Files: since file also lets you analyze the contents of the data, use file to quickly identify files that may not be what they claim (e.g., mislabeled extensions).
Key Options
- -b: Outputs just the file type without the file name.
- -i: Displays the MIME type of the file.
- -f : Reads filenames from a given file (one per line) and outputs their types.
- -L: Follows symbolic links and identifies the target file’s type.
- -s: Examines block or character special files to determine their type.
- –mime: Similar to -i, but shows both MIME type and encoding.
- -z: Inspects compressed files.
- –exclude : Excludes files or directories matching the given pattern.
- –help: Displays help and exits.
file -b example.txt
file -i image.jpg
file -f filelist.txt
file -L symlink
sudo file -s /dev/sda1
file --mime document.pdf
file -z archive.tar.gz
file --help
file -z archive.tar.gz
file --exclude=*.tmp *
Using find along with other commands to search inside and compare files
While the file command itself doesn’t directly search inside files or compare their contents, it can be combined with other Linux utilities like grep, cmp, and diff to create powerful workflows for searching, analyzing, and comparing files. Below, we outline practical techniques for these tasks, starting with content search and progressing to advanced comparisons.
You can see the full guide and cheat sheet here: Searching inside files and comparing their contents using Linux commands.
Common Usage Examples
Basic File Type Identification
To determine the type of a single file:
file document.txt
Check Multiple Files
To check the type of multiple files:
file file1 file2 file3
Checking MIME Types
For determining the MIME type of files:
file -i video.mp4
Handling Symbolic Links
To identify the target type of a symbolic link:
file -L symlink_to_binary
Processing a List of Files
Use a file containing a list of filenames:
file -f filelist.txt
Inspecting Compressed Files
To identify the contents of a compressed file:
file -z logs.tar.gz
Inspecting Device Files
For identifying device file types:
sudo file -s /dev/sda1
