file

FILE(1)                     General Commands Manual                    FILE(1)



NAME
       file - determine file type

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

DESCRIPTION
       This manual page documents version 4.17 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 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 formats (core files, tar archives) that are known
       to contain binary data.  When modifying the file /usr/share/file/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 Berkeley did and change ``shell commands
       text'' to ``shell script''.  Note that the file /usr/share/file/magic
       is built mechanically from a large number of small files in the
       subdirectory 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/file/magic.mgc , or /usr/share/file/magic if the compile
       file does not exist. In addition file will look in $HOME/.magic.mgc ,
       or $HOME/.magic for magic entries.

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

       -c, --checking-printout
               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, --compile
               Write a magic.mgc output file that contains a pre-parsed
               version of file.

       -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.

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

       -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 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, --keep-going
               Don't stop at the first match, keep going.

       -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 list
               Specify an alternate list of files containing magic numbers.
               This can be a single file, or a colon-separated list of files.
               If a compiled magic file is found alongside, it will be used
               instead.  With the -i or --mime option, the program adds
               ".mime" to each file name.

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

       -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(2) never read them.

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

       --help  Print a help message and exit.

FILES
       /usr/share/file/magic.mgc
              Default compiled list of magic numbers

       /usr/share/file/magic
              Default list of magic numbers

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

       /usr/share/file/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
       number file name.  If that variable is set, then file will not attempt
       to open $HOME/.magic .  file adds ".mime" and/or ".mgc" to the value of
       this variable as appropriate.  The environment variable POSIXLY_CORRECT
       controls (on systems that support symbolic links), if file will attempt
       to follow symlinks or not. If set, then file follows symlink, otherwise
       it does not. This is also controlled by the L and h options.

SEE ALSO
       magic(5) - description of magic file format.
       strings(1), od(1), hexdump(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 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  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
       consolidation 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
       incorrect.  If your old file command uses a magic file, keep the old
       magic file around for comparison purposes (rename it to
       /usr/share/file/magic.orig).

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, 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
       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 (christos@astron.com).

       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
       /usr/share/file/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
       public-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.

       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.

       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 for multiple character codes makes it even slower.

       This manual page, and particularly this section, is too long.

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



                          Copyright but distributable                  FILE(1)