Overview
The `file` command determines the type of a file by analyzing its content, rather than relying on its extension. It recognizes various formats such as text/binary, executable file formats (ELF), compressed files, images/audio, and can also output MIME types and encodings.
Key Features
- Determines type based on actual content, regardless of extension
- Can output MIME type and character encoding
- Can choose to identify the symbolic link target or the link itself
- Attempts to check inside compressed files (-z)
Example Usage Scenarios
Situations where the `file` command particularly shines.
- Identifying the actual format of a file with a misleading extension (e.g., a PDF disguised as a .jpg)
- Determining the type of files without extensions
- Branching processing in scripts based on file type
- Determining MIME types of uploaded files in web/network services
- Identifying the symbolic link itself or its target
- Analyzing content inside compressed files
- Identifying executable file formats in security analysis and forensics
Key Options
Commonly used options grouped by scenario.
1) Basic Operation & Output Control
2) Input/Target Specification
3) Magic Database/Exclusion/Debug
4) Help/Version
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Usage Examples
Common patterns are organized as examples.
Basic Identification
file /bin/lsOutputs file type in basic format
Brief Output Without Filename
file -b /bin/lsSimple output, easy to process in scripts
MIME Type/Encoding
file --mime-type index.html && file --mime-encoding README.mdUseful for type identification in web/pipelines
Check Inside Compressed Files
file -z backup.tar.gzEstimates the actual content of compressed files
Symbolic Link Itself vs. Target
file -h symlink && file -L symlinkExamine the link itself (-h) or follow the target (-L)
Bulk MIME Type Check with find
find . -type f -print0 | xargs -0 file --mime-typeSafely passes file lists using NUL delimiters
Magic Database Location
Paths may vary depending on the system and distribution.
🪄 Default Compiled Magic DB
/usr/share/file/magic.mgc
Default location for most distributions
📁 Source Magic Directory
/usr/share/file/magic/
Source rules before compilation (original, not .mgc)
Exit Codes
Refer to these when handling conditional logic in scripts.
| Code | Meaning |
|---|---|
| 0 | Success: Identification successful (or requested operation successful) |
| 1 | General problem: File not found/inaccessible/identification failed, etc. |
| 2 | Usage error or system error |
Installation
Mostly pre-installed, but if not, install with the following:
Debian/Ubuntu
sudo apt update && sudo apt install -y fileRHEL/CentOS/Fedora
sudo dnf install -y fileArch Linux
sudo pacman -S --needed fileopenSUSE
sudo zypper install -y fileTips & Cautions
- Using `--mime-type` and `--mime-encoding` explicitly can avoid differences in `-i/--mime` behavior across distributions/versions.
- Symbolic link handling: Use `-h` to examine the link itself, and `-L` to check the target file.
- When processing in bulk, using the `find -print0 | xargs -0` pattern ensures safety with filenames containing spaces/newlines.
- Depending on the compression format, `-z` may not always be able to check inside. If necessary, decompress first to check.