FILE(1) BSD General Commands Manual FILE(1)
file -- determine file type
file [-bchiklLNnprsvz0] [--apple] [--mime-encoding] [--mime-type] [-e testname] [-F separator] [-f namefile] [-m magicfiles] file ...
file -C [-m magicfiles]
This manual page documents version 5.11 of the file command.
file tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic
tests, and language tests. The first test that succeeds causes the file type to be printed.
The type printed will usually contain one of the words text (the file contains only printing characters and a few common control characters
and is probably safe to read on an ASCII terminal), executable (the file contains the result of compiling a program in a form understandable
to some UNIX kernel or another), or data meaning anything else (data is usually ``binary'' or non-printable). Exceptions are well-known file
formats (core files, tar archives) that are known to contain binary data. When modifying magic files or the program itself, make sure to
preserve these keywords. Users depend on knowing that all the readable files in a directory have the word ``text'' printed. Don't do as
Berkeley did and change ``shell commands text'' to ``shell script''.
The filesystem tests are based on examining the return from a stat(2) system call. The program checks to see if the file is empty, or if
it's some sort of special file. Any known file types appropriate to the system you are running on (sockets, symbolic links, or named pipes
(FIFOs) on those systems that implement them) are intuited if they are defined in the system header file <sys/stat.h>.
The magic tests are used to check for files with data in particular fixed formats. The canonical example of this is a binary executable
(compiled program) a.out file, whose format is defined in <elf.h>, <a.out.h> and possibly <exec.h> in the standard include directory. These
files have a ``magic number'' stored in a particular place near the beginning of the file that tells the UNIX operating system that the file
is a binary executable, and which of several types thereof. The concept of a ``magic'' has been applied by extension to data files. Any
file with some invariant identifier at a small fixed offset into the file can usually be described in this way. The information identifying
these files is read from the compiled magic file /usr/share/misc/magic.mgc, or the files in the directory /usr/share/misc/magic if the com-
piled file does not exist. In addition, if $HOME/.magic.mgc or $HOME/.magic exists, it will be used in preference to the system magic files.
If a file does not match any of the entries in the magic file, it is examined to see if it seems to be a text file. ASCII, ISO-8859-x, non-
ISO 8-bit extended-ASCII character sets (such as those used on Macintosh and IBM PC systems), UTF-8-encoded Unicode, UTF-16-encoded Unicode,
and EBCDIC character sets can be distinguished by the different ranges and sequences of bytes that constitute printable text in each set. If
a file passes any of these tests, its character set is reported. ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified as
``text'' because they will be mostly readable on nearly any terminal; UTF-16 and EBCDIC are only ``character data'' because, while they con-
tain text, it is text that will require translation before it can be read. In addition, file will attempt to determine other characteristics
of text-type files. If the lines of a file are terminated by CR, CRLF, or NEL, instead of the Unix-standard LF, this will be reported.
Files that contain embedded escape sequences or overstriking will also be identified.
Once file has determined the character set used in a text-type file, it will attempt to determine in what language the file is written. The
language tests look for particular strings (cf. <names.h>) that can appear anywhere in the first few blocks of a file. For example, the
keyword .br indicates that the file is most likely a troff(1) input file, just as the keyword struct indicates a C program. These tests are
less reliable than the previous two groups, so they are performed last. The language test routines also test for some miscellany (such as
Any file that cannot be identified as having been written in any of the character sets listed above is simply said to be ``data''.
Do not prepend filenames to output lines (brief mode).
Write a magic.mgc output file that contains a pre-parsed version of the magic file or directory.
Cause a checking printout of the parsed form of the magic file. This is usually used in conjunction with the -m flag to debug a new
magic file before installing it.
-e, --exclude testname
Exclude the test named in testname from the list of tests made to determine the file type. Valid test names are:
apptype EMX application type (only on EMX).
ascii Various types of text files (this test will try to guess the text encoding, irrespective of the setting of the 'encoding'
encoding Different text encodings for soft magic tests.
tokens Ignored for backwards compatibility.
cdf Prints details of Compound Document Files.
compress Checks for, and looks inside, compressed files.
elf Prints ELF file details.
soft Consults magic files.
tar Examines tar files.
-F, --separator separator
Use the specified string as the separator between the filename and the file result returned. Defaults to ':'.
-f, --files-from namefile
Read the names of the files to be examined from namefile (one per line) before the argument list. Either namefile or at least one
filename argument must be present; to test the standard input, use '-' as a filename argument. Please note that namefile is
unwrapped and the enclosed filenames are processed when this option is encountered and before any further options processing is done.
This allows one to process multiple lists of files with different command line arguments on the same file invocation. Thus if you
want to set the delimiter, you need to do it before you specify the list of files, like: ``-F @ -f namefile'', instead of: ``-f
namefile -F @''.
option causes symlinks not to be followed (on systems that support symbolic links). This is the default if the environment variable
POSIXLY_CORRECT is not defined.
Causes the file command to output mime type strings rather than the more traditional human readable ones. Thus it may say
'text/plain; charset=us-ascii' rather than ``ASCII text''.
Like -i, but print only the specified element(s).
Don't stop at the first match, keep going. Subsequent matches will be have the string '