How to Use File Command in Linux: Syntax and Examples

Use the file command in Linux to determine the type of a file by analyzing its content, not just its extension. Run file filename to see the file type information.

Syntax

The basic syntax of the file command is:

• file [options] filename

Here, filename is the name or path of the file you want to check. Options can modify the output or behavior.

bash

file filename

Example

This example shows how to use the file command to identify the type of a file named example.txt and a binary file /bin/ls.

bash

file example.txt
file /bin/ls

Output

example.txt: ASCII text
/bin/ls: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=..., stripped

Common Pitfalls

Common mistakes when using file include:

• Relying on file extensions instead of using file to check the actual content.
• Using file on directories without the -s option, which may not give detailed info.
• Not having permission to read the file, causing incomplete or no output.

Always ensure you have read access and use file -s for special files like devices or partitions.

bash

file myfile.pdf
file -s /dev/sda1

Output

myfile.pdf: PDF document, version 1.4
/dev/sda1: Linux rev 1.0 ext4 filesystem data, UUID=..., volume name "root"

Quick Reference

Option	Description
-b	Brief output, omit filename
-i	Output MIME type string
-s	Read special files like devices
-L	Follow symbolic links
--help	Show help message

Key Takeaways

Use file filename to identify the actual file type by content.

File extensions can be misleading; file reads file data to determine type.

Use options like -i for MIME type or -s for special files.

Ensure you have read permission to get accurate results.

The file command works on any file type including text, binaries, and devices.