What is the file command in UNIX?
The file command determines the file type of a file. It reports the file type in human readable format (e.g. ‘ASCII text’) or MIME type (e.g. ‘text/plain; charset=us-ascii’). As filenames in UNIX can be entirely independent of file type file can be a useful command to determine how to view or work with a file.
How to determine the file type of a file
To determine the file type of a file pass the name of a file to the file command.The file name along with the file type will be printed to standard output.
file file.txt
file.txt: ASCII text
To show just the file type pass the -b option.
file -b file.txt
ASCII text
The file command can be useful as filenames in UNIX bear no relation to their file type. So a file called somefile.csv could actually be a zip file. This can be verified by the file command.
file somefile.csv
somefile.csv: Zip archive data, at least v2.0 to extract
How to determine the file type of multiple files
The file command can also operate on multiple files and will output a separate line to standard output for each file.
file unix-*.md
unix-cat.md: ASCII text, with very long lines
unix-comm.md: ASCII text, with very long lines
unix-cut.md: UTF-8 Unicode text
unix-exit-status.md: ASCII text
unix-file.md: ASCII text, with very long lines
How to view the mime type of a file
To view the mime type of a file rather than the human readable format pass the -i option.
file -i file.txt
file.txt: text/plain; charset=us-ascii
This can be combined with the -b option to just show the mime type.
file -i -b file.txt
text/plain; charset=us-ascii
How to view compressed files without decompressing
To view compressed files without decompressing them pass the -z option. In the following example a file foo.txt.gz is a gzip compressed ASCII text file.
file -z bar.txt.gz
bar.txt.gz: ASCII text (gzip compressed data, was "bar.txt", last modified: Wed Sep 7 19:31:23 2016, from Unix)
Further reading
- file man page
- The Linux file command
- file (command) Wikipedia page
