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FILE(1)			  BSD General Commands Manual		       FILE(1)

NAME
     file -- determine file type

SYNOPSIS
     file [-vczL] [-f namefile]	[-m magicfiles]	file ...

DESCRIPTION
     This manual page documents	version	3.22 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 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 ASCII characters and	is probably safe to read on an ASCII
     terminal),	executable (the	file contains the result of compiling a	pro-
     gram in a form understandable to some UNIX	kernel or another), or data
     meaning anything else (data is usually `binary' or	non-printable).	 Ex-
     ceptions are well-known file formats (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.	 Don't do as Berkeley did - 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 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 num-
     ber' has been applied by extension	to data	files.	Any file with some in-
     variant identifier	at a small fixed offset	into the file can usually be
     described in this way.  The information in	these files is read from the
     magic file	/usr/share/misc/magic.

     If	an argument appears to be an ASCII file, file attempts to guess	its
     language.	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 tar(1)
     archives) and determine whether an	unknown	file should be labelled	as
     `ascii text' or `data'.

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

     -m	list
	     Specify an	alternate list of files	containing magic numbers.
	     This can be a single file,	or a colon-separated list of files.

     -z	     Try to look inside	compressed files.

     -c	     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.

     -f	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.

     -L	     Cause symlinks to be followed, as the like-named option in	ls(1).
	     (on systems that support symbolic links).

FILES
     /usr/share/misc/magic  default list of magic numbers (used	to be
			    /etc/magic in previous versions of FreeBSD)

ENVIRONMENT
     The environment variable MAGIC can	be used	to set the default magic num-
     ber files.

SEE ALSO
     od(1), strings(1),	magic(5)

STANDARDS CONFORMANCE
     This program is believed to exceed	the System V Interface Definition 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	pro-
     duce different (albeit more accurate) output 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

MAGIC DIRECTORY
     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
     /usr/share/misc/magic.orig).

HISTORY
     There has been a file command in every UNIX since at least	Research Ver-
     sion 6 (man page dated January, 1975).  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.  The program has undergone continued evolution
     since.

AUTHORS
     Written by	Ian F. Darwin <ian@sq.com>, UUCP address {utzoo	| ihnp4}!dar-
     win!ian, postal address: P.O. Box 603, Station F, Toronto,	Ontario,
     CANADA M4Y	2L8.

     Altered by
     Rob McMahon <cudcv@warwick.ac.uk>,	1989, to extend	the `&'	operator from
     simple `x&y != 0' to `x&y op z'.

     Altered by
     Guy Harris	<guy@auspex.com>, 1993,	to:

	   put the ``old-style'' `&' operator back the way it was, because

		 1.   Rob McMahon's change broke the previous style of usage,

		 2.   The SunOS	``new-style'' `&' operator, which this version
		      of file supports,	also handles `x&y op z',

		 3.   Rob's change wasn't documented in	any case;

	   put in multiple levels of `>';

	   put in ``beshort'', ``leshort'', etc. keywords to look at numbers
	   in the file in a specific byte order, rather	than in	the native
	   byte	order of the process running file.

     Changes by
     Ian Darwin	and various authors including
     Christos Zoulas <christos@deshaw.com>, 1990-1992.

LEGAL NOTICE
     Copyright (c) Ian F. Darwin, Toronto, Canada, 1986, 1987, 1988, 1989,
     1990, 1991, 1992, 1993.

     This software is not subject to and may not be made subject to any	li-
     cense of the American Telephone and Telegraph Company, Sun	Microsystems
     Inc., Digital Equipment Inc., Lotus Development Inc., the Regents of the
     University	of California, The X Consortium	or MIT,	or The Free Software
     Foundation.

     This software is not subject to any export	provision of the United	States
     Department	of Commerce, and may be	exported to any	country	or planet.

     Permission	is granted to anyone to	use this software for any purpose on
     any computer system, and to alter it and redistribute it freely, subject
     to	the following restrictions:

	   1.	The author is not responsible for the consequences of use of
		this software, no matter how awful, even if they arise from
		flaws in it;

	   2.	The origin of this software must not be	misrepresented,	either
		by explicit claim or by	omission.  Since few users ever	read
		sources, credits must appear in	the documentation;

	   3.	Altered	versions must be plainly marked	as such, and must not
		be misrepresented as being the original	software.  Since few
		users ever read	sources, credits must appear in	the documenta-
		tion;

	   4.	This notice may	not be removed or altered.

     A few support files ( getopt(), strtok()) distributed with	this package
     are by Henry Spencer and are subject to the same terms as above.

     A few simple support files	( strtol(), strchr()) distributed with this
     package are in the	public domain; they are	so marked.

     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 restrictions.

BUGS
     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.

     File uses several algorithms that favor speed over	accuracy, thus it can
     be	misled about the contents of ASCII files.

     The support for ASCII 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 doesn't grok FORTRAN.	It should be able to figure FORTRAN by
     seeing some keywords which	appear indented	at the start of	line.  Regular
     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 optimization 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 don't pan out, it should be
     possible to use the first guess.

     This program is slower than some vendors' file commands.

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

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

BSD				 July 30, 1997				   BSD

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | ENVIRONMENT | SEE ALSO | STANDARDS CONFORMANCE | MAGIC DIRECTORY | HISTORY | AUTHORS | LEGAL NOTICE | BUGS | AVAILABILITY

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