FreeBSD Man Pages

file(1)

NAME

     file -- determine file type

SYNOPSIS

     file [-bciknNsvzL] [-f namefile] [-F separator] [-m magicfiles] file ...
     file -C [-m magicfile]

DESCRIPTION

     This manual page documents version 3.41 of the file utility which tests
     each argument in an attempt to classify it.  There are three sets of
     tests, performed in this order: file system 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 for-
     mats (core files, tar archives) that are known to contain binary data.
     When modifying the file /usr/share/misc/magic or the program itself,
     preserve these keywords.  People depend on knowing that all the readable
     files in a directory have the word ``text'' printed.  Don't do as Berke-
     ley 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 distribu-
     tion of this program.

     The file system 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 sys-
     tem 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 particu-
     lar 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 exe-
     cutable, 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/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, 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''
     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 lan-
     guage tests look for particular strings (cf names.h) that can appear any-
     where 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''.

OPTIONS

     -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.

     -F separator
	     Use the specified separator character instead of `:'.

     -i      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      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 checking a list of files.  It is intended to be
	     used by programs that want filetype output from a pipe.

     -N      Don't pad output to align filenames nicely.

     -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).

	     stat(2) since on some systems it reports a zero size for raw disk
	     partitions.

FILES

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

ENVIRONMENT

     The environment variable MAGIC can be used to set the default magic num-
     ber files.

SEE ALSO

     hexdump(1), od(1), strings(1), magic(5)

STANDARDS CONFORMANCE

     This program is believed to exceed the System V Interface Definition,
     Fourth Edition (``SVID4'') of FILE(CMD), as near as one can determine
     from the vague language contained therein.  Its behaviour 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(1) com-
     mand 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 contributed by various authors.  Christos Zoulas (address
     below) will collect additional or corrected magic file entries.  A con-
     solidation 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 incor-

		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}	     # Linux
     /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 -s /dev/rwd0e			     # BSD
     /dev/rwd0e:
     Unix Fast File system (little-endian),
     last mounted on /usr,
     last written at Mon Feb 10 13:22:40 2003,
     clean flag 2,
     number of blocks 28754208,
     number of data blocks 27812712,
     number of cylinder groups 3566,
     block size 8192,
     fragment size 1024,
     minimum percentage of free blocks 5,
     rotational delay 0ms,
     disk rotational speed 60rps,
     TIME optimization

     $ 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

HISTORY

     There has been a file command in every UNIX since at least Research Ver-
     sion 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.

     ter codes and attempt to identify the languages of non-ASCII files.

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

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 pub-
     lic-domain tar program, 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?	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.

     The file utility 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 sim-
     plistic, inefficient 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 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

FreeBSD 5.4		       February 27, 2003		   FreeBSD 5.4

SPONSORED LINKS