Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
FILE(1)			  BSD General Commands Manual		       FILE(1)

     file -- determine file type

     file [-bchikLnNprsvz] [-f namefile] [-F separator]	[-m magicfiles]
	  file ...
     file -C [-m magicfile]

     This manual page documents	version	4.21 of	the file utility which tests
     each argument in an attempt to classify it.  There	are three sets of
     tests, performed in this order: file system tests,	magic number 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 for-
     mats (core	files, tar archives) that are known to contain binary data.
     When modifying the	file /usr/share/misc/magic or the program itself,
     preserve these keywords.  People depend on	knowing	that all the readable
     files in a	directory have the word	"text" printed.	 Do not	do as Berkeley
     did and change "shell commands text" to "shell script".  Note that	the
     file /usr/share/misc/magic	is built mechanically from a large number of
     small files in the	subdirectory Magdir in the source distribution of this

     The file system 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 is
     some sort of special file.	 Any known file	types appropriate to the sys-
     tem 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 number tests are	used to	check for files	with data in particu-
     lar fixed formats.	 The canonical example of this is a binary executable
     (compiled program)	a.out file, whose format is defined in <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 exe-
     cutable, and which	of several types thereof.  The concept of `magic
     number' 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
     /usr/share/misc/magic if the compile file does not	exist.	In addition
     file will look in $HOME/.magic.mgc, or $HOME/.magic for magic entries.

     If	a file does not	match any of the entries in the	magic file, it is ex-
     amined 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" be-
     cause they	will be	mostly readable	on nearly any terminal;	UTF-16 and
     EBCDIC are	only "character	data" because, while they contain 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 es-
     cape 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 lan-
     guage tests look for particular strings (cf names.h) that can appear any-
     where 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 tar(1) archives).

     Any file that cannot be identified	as having been written in any of the
     character sets listed above is simply said	to be "data".

     -b, --brief
	     Do	not prepend filenames to output	lines (brief mode).

     -c, --checking-printout
	     Cause a checking printout of the parsed form of the magic file.
	     This is usually used in conjunction with -m to debug a new	magic
	     file before installing it.

     -C, --compile
	     Write a magic.mgc output file that	contains a pre-parsed version
	     of	file.

     -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.

     -F, --separator separator
	     Use the specified string as the separator between the filename
	     and the file result returned.  Defaults to	`:'.

     -h, --no-dereference
	     Causes symlinks not to be followed	(on systems that support sym-
	     bolic links).  This is the	default	if the environment variable
	     POSIXLY_CORRECT is	not defined.

     -i, --mime
	     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".  In or-
	     der for this option to work, file changes the way it handles
	     files recognised by the command itself (such as many of the text
	     file types, directories etc), and makes use of an alternative
	     magic file.  (See FILES section, below).

     -k, --keep-going
	     Do	not stop at the	first match, keep going.

     -L, --dereference
	     option causes symlinks to be followed, as the like-named option
	     in	ls(1) (on systems that support symbolic	links).	 This is the
	     default if	the environment	variable POSIXLY_CORRECT is defined.

     -m, --magic-file list
	     Specify an	alternate list of files	containing magic numbers.
	     This can be a single file,	or a colon-separated list of files.
	     If	a compiled magic file is found alongside, it will be used in-
	     stead.  With the -i or --mime option, the program adds .mime to
	     each file name.

     -n, --no-buffer
	     Force stdout to be	flushed	after checking each file.  This	is
	     only useful if checking a list of files.  It is intended to be
	     used by programs that want	filetype output	from a pipe.

     -N, --no-pad
	     Do	not pad	filenames so that they align in	the output.

     -p, --preserve-date
	     On	systems	that support utime(3) or utimes(2), attempt to pre-
	     serve the access time of files analyzed, to pretend that file
	     never read	them.

     -r, --raw
	     Do	not translate unprintable characters to	\ooo.  Normally	file
	     translates	unprintable characters to their	octal representation.

     -s, --special-files
	     Normally, file only attempts to read and determine	the type of
	     argument files which stat(2) reports are ordinary files.  This
	     prevents problems,	because	reading	special	files may have pecu-
	     liar consequences.	 Specifying the	-s option causes file to also
	     read argument files which are block or character special files.
	     This is useful for	determining the	file system types of the data
	     in	raw disk partitions, which are block special files.  This op-
	     tion also causes file to disregard	the file size as reported by
	     stat(2) since on some systems it reports a	zero size for raw disk

     -v, --version
	     Print the version of the program and exit.

     -z, --uncompress
	     Try to look inside	compressed files.

     --help  Print a help message and exit.

     /usr/share/misc/magic.mgc	 Default compiled list of magic	numbers
     /usr/share/misc/magic	 Default list of magic numbers
				 Default compiled list of magic	numbers, used
				 to output mime	types when the -i option is
     /usr/share/misc/magic.mime	 Default list of magic numbers,	used to	output
				 mime types when the -i	option is specified.

     The environment variable MAGIC can	be used	to set the default magic num-
     ber file name.  If	that variable is set, then file	will not attempt to
     open $HOME/.magic.	 file adds .mime and/or	.mgc to	the value of this
     variable as appropriate.  The environment variable	POSIXLY_CORRECT	con-
     trols (on systems that support symbolic links), if	file will attempt to
     follow symlinks or	not.  If set, then file	follows	symlink, otherwise it
     does not.	This is	also controlled	by the -L and -h options.

     hexdump(1), od(1),	strings(1), magic(5)

     This program is believed to exceed	the System V Interface Definition,
     Fourth Edition ("SVID4") of FILE(CMD), as near as one can determine from
     the vague language	contained therein.  Its	behaviour is mostly compatible
     with the System V program of the same name.  This version knows more
     magic, however, so	it will	produce	different (albeit more accurate) out-
     put in many cases.

     The one significant difference between this version and System V is that
     this version treats any white space as a delimiter, so that spaces	in
     pattern strings must be escaped.  For example,

	   >10	string	  language impress    (imPRESS data)

     in	an existing magic file would have to be	changed	to

	   >10	string	  language\ impress   (imPRESS data)

     In	addition, in this version, if a	pattern	string contains	a backslash,
     it	must be	escaped.  For example

	   0	string	       \begindata     Andrew Toolkit document

     in	an existing magic file would have to be	changed	to

	   0	string	       \\begindata    Andrew Toolkit document

     SunOS releases 3.2	and later from Sun Microsystems	include	a file(1) com-
     mand derived from the System V one, but with some extensions.  My version
     differs from Sun's	only in	minor ways.  It	includes the extension of the
     `&' operator, used	as, for	example,

	   >16	long&0x7fffffff	    >0	      not stripped

     The magic file entries have been collected	from various sources, mainly
     USENET, and contributed by	various	authors.  Christos Zoulas (address be-
     low) will collect additional or corrected magic file entries.  A consoli-
     dation of magic file entries will be distributed periodically.

     The order of entries in the magic file is significant.  Depending on what
     system you	are using, the order that they are put together	may be incor-
     rect.  If your old	file command uses a magic file,	keep the old magic
     file around for comparison	purposes (rename it to

     $ file file.c file	/dev/{wd0a,hda}
     file.c:	C program text
     file:	ELF 32-bit LSB executable, Intel 80386,	version	1 (SYSV),
		dynamically linked (uses shared	libs), stripped
     /dev/wd0a:	block special (0/0)
     /dev/hda:	block special (3/0)
     $ file -s /dev/wd0{b,d}
     /dev/wd0b:	data
     /dev/wd0d:	x86 boot sector
     $ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10}
     /dev/hda:	 x86 boot sector
     /dev/hda1:	 Linux/i386 ext2 filesystem
     /dev/hda2:	 x86 boot sector
     /dev/hda3:	 x86 boot sector, extended partition table
     /dev/hda4:	 Linux/i386 ext2 filesystem
     /dev/hda5:	 Linux/i386 swap file
     /dev/hda6:	 Linux/i386 swap file
     /dev/hda7:	 Linux/i386 swap file
     /dev/hda8:	 Linux/i386 swap file
     /dev/hda9:	 empty
     /dev/hda10: empty

     $ file -i file.c file /dev/{wd0a,hda}
     file.c:	text/x-c
     file:	application/x-executable, dynamically linked (uses shared libs),
		not stripped
     /dev/hda:	application/x-not-regular-file
     /dev/wd0a:	application/x-not-regular-file

     There has been a file command in every UNIX since at least	Research Ver-
     sion 4 (man page dated November, 1973).  The System V version introduced
     one significant major change: the external	list of	magic number types.
     This slowed the program down slightly but made it a lot more flexible.

     This program, based on the	System V version, was written by Ian Darwin
     <> without looking at anybody else's source code.

     John Gilmore revised the code extensively,	making it better than the
     first version.  Geoff Collyer found several inadequacies and provided
     some magic	file entries.  Contributions by	the `&'	operator by Rob
     McMahon <>, 1989.

     Guy Harris	<>, made many changes from 1993 to the present.

     Primary development and maintenance from 1990 to the present by Christos
     Zoulas <>.

     Altered by	Chris Lowth <>, 2000: Handle the	-i option to
     output mime type strings and using	an alternative magic file and internal

     Altered by	Eric Fischer <>, July, 2000, to identify charac-
     ter codes and attempt to identify the languages of	non-ASCII files.

     The list of contributors to the Magdir directory (source for the
     /usr/share/misc/magic file) is too	long to	include	here.  You know	who
     you are; thank you.

     Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.  Covered by the
     standard Berkeley Software	Distribution copyright;	see the	file
     LEGAL.NOTICE in the source	distribution.

     The files tar.h and is_tar.c were written by John Gilmore from his	pub-
     lic-domain	tar program, and are not covered by the	above license.

     There must	be a better way	to automate the	construction of	the Magic file
     from all the glop in Magdir.  What	is it?	Better yet, the	magic file
     should be compiled	into binary (say, ndbm(3) or, better yet, fixed-length
     ASCII strings for use in heterogenous network environments) for faster
     startup.  Then the	program	would run as fast as the Version 7 program of
     the same name, with the flexibility of the	System V version.

     The file utility uses several algorithms that favor speed over accuracy,
     thus it can be misled about the contents of text files.

     The support for text files	(primarily for programming languages) is sim-
     plistic, inefficient and requires recompilation to	update.

     There should be an	else clause to follow a	series of continuation lines.

     The magic file and	keywords should	have regular expression	support.
     Their use of ASCII	TAB as a field delimiter is ugly and makes it hard to
     edit the files, but is entrenched.

     It	might be advisable to allow upper-case letters in keywords for e.g.,
     troff(1) commands vs man page macros.  Regular expression support would
     make this easy.

     The program does not grok FORTRAN.	 It should be able to figure FORTRAN
     by	seeing some keywords which appear indented at the start	of line.  Reg-
     ular expression support would make	this easy.

     The list of keywords in ascmagic probably belongs in the Magic file.
     This could	be done	by using some keyword like `*' for the offset value.

     Another optimisation would	be to sort the magic file so that we can just
     run down all the tests for	the first byte,	first word, first long,	etc,
     once we have fetched it.  Complain	about conflicts	in the magic file en-
     tries.  Make a rule that the magic	entries	sort based on file offset
     rather than position within the magic file?

     The program should	provide	a way to give an estimate of "how good"	a
     guess is.	We end up removing guesses (e.g. "From " as first 5 chars of
     file) because they	are not	as good	as other guesses (e.g. "Newsgroups:"
     versus "Return-Path:").  Still, if	the others do not pan out, it should
     be	possible to use	the first guess.

     This program is slower than some vendors' file commands.  The new support
     for multiple character codes makes	it even	slower.

     This manual page, and particularly	this section, is too long.

     You can obtain the	original author's latest version by anonymous FTP on in the directory /pub/file/file-X.YZ.tar.gz

BSD				August 18, 2005				   BSD


Want to link to this manual page? Use this URL:

home | help