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NAME    [Toc]    [Back]

       file - determine file type

SYNOPSIS    [Toc]    [Back]

       file [ -bciknsvzL ] [ -f namefile ] [ -m magicfiles ] file ...
       file -C [ -m magicfile ]

DESCRIPTION    [Toc]    [Back]

       This manual page documents version 3.37-3.1 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  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  adding  local definitions to /etc/magic, 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 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 program.

       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 number 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
       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 `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 /etc/magic and the compiled  magic  file
       /usr/share/misc/magic.mgc  ,  or  /usr/share/misc/magic	if the compile
       file does not exist.

       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, nonISO
 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 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 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	tar(1)

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

OPTIONS    [Toc]    [Back]

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

       -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.

       -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
	       order  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
	       Don't stop at the first match, keep going.

       -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.

       -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.

       -v      Print the version of the program and exit.

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

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

       -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 peculiar
 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 filesystem types  of
	       the data in raw disk partitions, which are block special files.
	       This option 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 partitions.

       --help  Print a help message and exit.

	       Print version information and exit.

FILES    [Toc]    [Back]

	      Default compiled list of magic numbers

	      Default list of magic numbers

	      Default list of magic numbers, used to output  mime  types  when
	      the -i option is specified.

	      Local additions to magic wisdom.

ENVIRONMENT    [Toc]    [Back]

       The  environment  variable  MAGIC  can be used to set the default magic
       number files.

SEE ALSO    [Toc]    [Back]

       magic(5) - description of magic file format.
       strings(1), od(1), hexdump(1) - tools for examining non-textfiles.


       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 produce 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)
       command	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    [Toc]    [Back]

       The magic file entries have been collected from various sources, mainly
       USENET, and contributed by various authors.  Christos  Zoulas  (address
       below) will collect additional or corrected magic file entries.	A consolidation
 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

EXAMPLES    [Toc]    [Back]

       $ file file.c file /dev/hda
       file.c:	 C program text
       file:	 ELF 32-bit LSB executable, Intel 80386, version 1,
		 dynamically linked, not stripped
       /dev/hda: block special

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

HISTORY    [Toc]    [Back]

       There has been a file command in every UNIX  since  at  least  Research
       Version	6  (man  page  dated  January 16, 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
       <ian@darwinsys.com> 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, cudcv@warwick.ac.uk, 1989.

       Guy Harris, guy@netapp.com, made many changes from 1993 to the present.

       Primary	development and maintenance from 1990 to the present by Christos
 Zoulas (christos@astron.com).

       Altered by Chris Lowth, chris@lowth.com, 2000: Handle the ``-i'' option
       to  output  mime  type  strings and using an alternative magic file and
       internal logic.

       Altered by Eric Fischer (enf@pobox.com), July, 2000, to identify  character
 codes and attempt to identify the languages of non-ASCII files.

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

LEGAL NOTICE    [Toc]    [Back]

       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 public-domain
 tar program, and are not covered by the above license.

BUGS    [Toc]    [Back]

       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 text files.

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

       There should be an ``else'' clause to follow a series  of  continuation

       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	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 entries.  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.  The new support
 for multiple character codes makes it even slower.

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

AVAILABILITY    [Toc]    [Back]

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

       This Debian version adds long options and corrects some bugs. It can be
       obtained from every site carrying a Debian distribution (ftp.debian.org
       and mirrors).

Debian/GNU Linux		 October 2001			       FILE(1)
[ Back ]
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