FILE(1)							  FILE(1)


file - determine file type

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

DESCRIPTION
       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 prob-
       ably 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 the file /etc/magic or  the  program
       itself,	preserve these keywords .  People depend on know-
       ing 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 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	 informa-
       tion   in   these  files	 is  read  from	 the  magic  file
       /etc/magic.

       If an argument appears to be an ASCII file, file	 attempts
       to  guess  its language.	 The language tests look for par-
       ticular 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  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
       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 conjunc-
	       tion 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      option  causes  symlinks	 to  be	 followed, as the
	       like-named option in ls(1).  (on systems that sup-
	       port symbolic links).

FILES
       /etc/magic - default list of magic numbers

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

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

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  behavior  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 `&' opera-
       tor, 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  below)  will  collect
       additional  or corrected magic file entries.  A consolida-
       tion of magic file entries will	be  distributed	 periodi-
       cally.

       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 incorrect.	 If your old file
       command uses a magic file, keep the old magic file  around
       for comparison purposes (rename it to /etc/magic.orig).

HISTORY
       There has been a file command in every UNIX since at least
       Research Version 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 bet-
       ter than the first version.  Geoff Collyer  found  several
       inadequacies  and  provided  some magic file entries.  The
       program has undergone continued evolution since.

AUTHOR
       Written	by  Ian	 F.  Darwin,  UUCP   address   {utzoo	|
       ihnp4}!darwin!ian,  Internet  address  ian@sq.com,  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 pre-
	      vious  style  of	usage, 2) the SunOS ``new-style''
	      `&' operator, which this version of file	supports,
	      also handles `x&y op z', and 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 Chris-
       tos Zoulas (christos@ee.cornell.edu), 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 sub-
       ject to any license of the American  Telephone  and  Tele-
       graph  Company,	Sun  Microsystems Inc., Digital Equipment
       Inc., Lotus Development Inc., the Regents of  the  Univer-
       sity  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	 restric-
       tions:

       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 documenta-
       tion.

       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 documentation.

       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 public-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  Ver-
       sion  7	program of the same name, with the flexibility of
       the System V version.

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

       The support for ASCII  files  (primarily	 for  programming
       languages)  is simplistic, inefficient and requires recom-
       pilation 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  key-
       words  for e.g., troff commands vs man page macros.  Regu-
       lar 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	 entries.
       Make a rule that the magic entries sort based on file off-
       set 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  tesla.ee.cornell.edu	 in the directory
       /pub/file-X.YY.tar.gz



















		   Copyright but distributable			6


