Home Man
Today's Posts

Linux & Unix Commands - Search Man Pages

RedHat 9 (Linux i386) - man page for file (redhat section 1)

FILE(1) 			     General Commands Manual				  FILE(1)

       file - determine file type

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

       This manual page documents version 3.39 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 print-
       ing 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  modifying  the   file
       /usr/share/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  and  change ``shell commands text'' to ``shell script''.  Note that the
       file /usr/share/magic is built mechanically from a large number of small files in the sub-
       directory 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  the  compiled  magic  file /usr/share/magic.mgc , or /usr/share/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, 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  addi-
       tion,  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) 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''.

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

       -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.

       -C      Write a magic.mgc output file that contains a pre-parsed version of file.

       -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.

       -i      Causes the file command to output mime type strings rather than	the  more  tradi-
	       tional  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      Don't stop at the first match, keep going.

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

       -n      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.

       -v      Print the version of the program and exit.

       -z      Try to look inside compressed files.

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

       -s      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.

       /usr/share/magic.mgc - defaults compiled list of magic numbers

       /usr/share/magic - default list of magic numbers

       /usr/share/magic.mime - default list of magic numbers, used to output mime types when  the
       -i option is specified.

       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), 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   long0x7fffffff 0	     not stripped

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

       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

       $ 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, dynamically linked (uses shared libs),
       not stripped
       /dev/hda:    application/x-not-regular-file
       /dev/wd0a:   application/x-not-regular-file

       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 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 (chris-

       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.

       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  pro-
       gram, and are not covered by the above license.

       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,  ineffi-
       cient 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 key-
       words 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.

       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

				   Copyright but distributable				  FILE(1)

All times are GMT -4. The time now is 11:44 PM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
Show Password