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Linux 2.6 - man page for file (linux section 1)

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

NAME
     file -- determine file type

SYNOPSIS
     file [-bchikLNnprsvz0] [--apple] [--mime-encoding] [--mime-type] [-e testname]
	  [-F separator] [-f namefile] [-m magicfiles] file ...
     file -C [-m magicfiles]
     file [--help]

DESCRIPTION
     This manual page documents version 5.04 of the file command.

     file tests each argument in an attempt to classify it.  There are three sets of tests, per-
     formed in this order: filesystem tests, magic 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 ter-
     minal), executable (the file contains the result of compiling a program in a form under-
     standable 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 ar-
     chives) that are known to contain binary data.  When adding local definitions to /etc/magic,
     make sure to preserve these keywords.  Users 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'.

     The filesystem tests are based on examining the return from a stat(2) system call.  The pro-
     gram 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 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 <elf.h>, <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 a 'magic' 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 the compiled magic file /usr/share/misc/magic.mgc, or the files in the
     directory /usr/share/misc/magic if the compiled file does not exist. In addition, if
     $HOME/.magic.mgc or $HOME/.magic exists, it will be used in preference to the system magic
     files.

     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, 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' 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 previ-
     ous 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'.

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

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

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

     -e, --exclude testname
	     Exclude the test named in testname from the list of tests made to determine the file
	     type. Valid test names are:

	     apptype   EMX application type (only on EMX).

	     text      Various types of text files (this test will try to guess the text encod-
		       ing, irrespective of the setting of the 'encoding' option).

	     encoding  Different text encodings for soft magic tests.

	     tokens    Looks for known tokens inside text files.

	     cdf       Prints details of Compound Document Files.

	     compress  Checks for, and looks inside, compressed files.

	     elf       Prints ELF file details.

	     soft      Consults magic files.

	     tar       Examines tar files.

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

     -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.

     -h, --no-dereference
	     option causes symlinks not to be followed (on systems that support symbolic 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 order for this option to work, file changes the way it handles
	     files recognized by the command itself (such as many of the text file types, direc-
	     tories etc), and makes use of an alternative 'magic' file.  (See the FILES section,
	     below).

     --mime-type, --mime-encoding
	     Like -i, but print only the specified element(s).

     -k, --keep-going
	     Don't stop at the first match, keep going. Subsequent matches will be have the
	     string '\012- ' prepended.  (If you want a newline, see the '-r' option.)

     -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 magicfiles
	     Specify an alternate list of files and directories containing magic.  This can be a
	     single item, or a colon-separated list.  If a compiled magic file is found alongside
	     a file or directory, it will be used instead.

     -N, --no-pad
	     Don't pad filenames so that they align in the output.

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

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

     -r, --raw
	     Don't translate unprintable characters to \ooo.  Normally file translates unprint-
	     able 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 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.

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

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

     -0, --print0
	     Output a null character '\0' after the end of the filename. Nice to cut(1) the out-
	     put. This does not affect the separator which is still printed.

     --help  Print a help message and exit.

FILES
     /usr/share/misc/magic.mgc	Default compiled list of magic.
     /usr/share/misc/magic	Directory containing default magic files.

ENVIRONMENT
     The environment variable MAGIC can be used to set the default magic file name.  If that
     variable is set, then file will not attempt to open $HOME/.magic.	file adds '.mgc' to the
     value of this variable as appropriate.  However, file has to exist in order for file.mime to
     be considered.  The environment variable POSIXLY_CORRECT controls (on systems that support
     symbolic links), whether file will attempt to follow symlinks or not. If set, then file fol-
     lows symlink, otherwise it does not. This is also controlled by the -L and -h options.

SEE ALSO
     magic(5), strings(1), od(1), hexdump(1), file(1posix)

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 com-
     patible 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 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
     The magic file entries have been collected from various sources, mainly USENET, and contrib-
     uted by various authors.  Christos Zoulas (address below) will collect additional or cor-
     rected magic file entries.  A consolidation of magic file entries will be distributed peri-
     odically.

     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.

EXAMPLES
	   $ 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
	   /dev/hda:	application/x-not-regular-file
	   /dev/wd0a:	application/x-not-regular-file

HISTORY
     There has been a file command in every UNIX since at least Research Version 4 (man page
     dated November, 1973).  The System V version introduced one significant major change: the
     external list of magic 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 (chris-
     tos@astron.com).

     Altered by Chris Lowth, chris@lowth.com, 2000: Handle the -i option to output mime type
     strings, 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.

     Altered by Reuben Thomas (rrt@sc3d.org), 2007 to 2008, to improve MIME support and merge
     MIME and non-MIME magic, support directories as well as files of magic, apply many bug fixes
     and improve the build system.

     The list of contributors to the 'magic' directory (magic files) is too long to include here.
     You know who you are; thank you.  Many contributors are listed in the source files.

LEGAL NOTICE
     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(1) pro-
     gram, and are not covered by the above license.

BUGS
     There must be a better way to automate the construction of the Magic file from all the glop
     in Magdir.  What is it?

     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.

     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.

     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.  'Fromas 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 manual page, and particularly this section, is too long.

RETURN CODE
     file returns 0 on success, and non-zero on error.

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

     This Debian version adds a number of new magic entries. It can be obtained from every site
     carrying a Debian distribution (that is ftp.debian.org and mirrors).

BSD					 October 9, 2008				      BSD


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