file

Use

file unknown-data

What It Does

file guesses what kind of data a path contains by inspecting bytes and metadata. It does not rely only on the filename extension.

Practice

Use it before choosing text, archive, compression, or binary inspection tools.

file /bin/ls
file /etc/passwd
file ~/src/pages/index.md
file archive.tar.gz

file compares the beginning bytes against known signatures, checks whether bytes look like text in an encoding, and uses filesystem metadata where useful. The result is a strong hint, not a mathematical proof.

Watch Out

File extensions are conventions, not proof.

If file says ELF, you are looking at a Linux executable or library. If it says ASCII text or UTF-8 Unicode text, text tools are usually safe.

Docs Pointers

• Run man file.
• Read file encoding, file, and number bases.