file(1)

file -- determine file type

Synopsis

file [-h] [-m mfile] [-f ffile] arg ...

file [-h] [-m mfile] -f ffile

file -c [-m mfile]

Description

file performs a series of tests on each file supplied by arg and, optionally, on each file supplied in ffile in an attempt to classify it. If arg appears to be a text file, file examines the first 512 bytes and tries to guess its programming language. If arg is an executable a.out, file prints the version stamp, provided it is greater than 0. If arg is a symbolic link, by default the link is followed and file tests the file that the symbolic link references.

-c: Check the magic file for format errors. For reasons of efficiency, this validation is normally not carried out.
-f ffile: ffile contains the names of the files to be examined.
-h: Do not follow symbolic links.
-m mfile: Use mfile as an alternate magic file, instead of /etc/magic.

file uses /etc/magic to identify files that have a magic number. A magic number is a numeric or string constant that indicates the file type. Commentary at the beginning of /etc/magic explains its format.

file classifies files containing supplementary code set characters according to the locale specified in the LC_CTYPE environment variable (see LANG on environ(5)). file reads each argument and can distinguish data files, program text files, shell scripts, and executable files as follows:

Files Classification

Data files containing supplementary characters data

Shell scripts containing supplementary characters command text

Language program text files containing literals or comments using supplementary characters xxx text

Executable files executable

Files	Classification
Data files containing supplementary characters	data
Shell scripts containing supplementary characters	command text
Language program text files containing literals or comments using supplementary characters	*xxx* text
Executable files	executable

Environment variables

If POSIX2 is set, error messages are printed to standard output rather than to standard error.

Files

/etc/magic
/usr/lib/locale/locale/LC_MESSAGES/uxcore: language-specific message file (See LANG on environ(5).)

References

filehdr(4)

Diagnostics

If the -h option is specified and arg is a symbolic link, file prints the error message: UX:file:ERROR:symbolic link to arg