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RocketLink!--> Man page versions: OpenBSD FreeBSD NetBSD RedHat Solaris Others

FILE(1)                                                   FILE(1)

       file - determine file type

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

       This manual page documents version 3.22 of the  file  com-
       mand.   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

       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

                  Copyrighted but distributable                 1

FILE(1)                                                   FILE(1)

       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  pro-
       gram.  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'.

       -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).

       /etc/magic - default list of magic numbers

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

       magic(5) - description of magic file format.
       strings(1), od(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

                  Copyrighted but distributable                 2

FILE(1)                                                   FILE(1)

       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

       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-

       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).

       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

       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.

       Written by Ian F. Darwin, ian@darwinsys.com.

       Altered  by  Rob  McMahon,  cudcv@warwick.ac.uk,  1989, to

                  Copyrighted but distributable                 3

FILE(1)                                                   FILE(1)

       extend the `&' operator from simple `x&y != 0' to `x&y  op

       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@deshaw.com), 1990-1997.

       This program is distributed under the terms of the  accom-
       panying license file LEGAL.NOTICE.

       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

       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.

       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

       The support for ASCII  files  (primarily  for  programming
       languages)   is   simplistic,   inefficient  and  requires

                  Copyrighted but distributable                 4

FILE(1)                                                   FILE(1)

       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

       It might be advisable to allow upper-case letters in  key-
       words  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 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

       You can obtain the original  author's  latest  version  by
       anonymous  FTP  at  ftp://ftp.astron.com/pub/file/  with a
       name like file-X.YY.tar.gz .

                  Copyrighted but distributable                 5

Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.

(Corrections, notes, and links courtesy of RocketAware.com)

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