Provided by: file_4.21-3_i386 bug

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 4.21 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 adding local definitions to /etc/magic, 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
     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 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 /etc/magic and the compiled magic file
     /usr/share/file/magic.mgc, or /usr/share/file/magic if the compiled 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 the -m flag to debug a
             new magic file before installing it.

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

     -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
                Check for EMX application type (only on EMX).

             ascii
                Check for various types of ascii files.

             compress
                Don’t look for, or inside compressed files.

             elf
                Don’t print elf details.

             fortran
                Don’t look for fortran sequences inside ascii files.

             soft
                Don’t consult magic files.

             tar
                Don’t examine tar files.

             token
                Don’t look for known tokens inside ascii files.

             troff
                Don’t look for troff sequences inside ascii files.

     -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 recognized 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. Subsequent matches
             will be prepended by “\012- ”.  (If you want a newline, see “-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 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
             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.

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

     --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.  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), 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), strings(1), od(1), hexdump(1)

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 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 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.

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(1) 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?

     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.  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.

     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.

RETURN CODE

     file almost always returns 0. It returns a different code if it cannot
     open a file.

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 magix entries. It can be
     obtained from every site carrying a Debian distribution (that is
     ftp.debian.org and mirrors).