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    Command:

    file

    
              [-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, performed 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 terminal), executable (the file con-
         tains 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 modify-
         ing magic files or the program itself, 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 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
    
         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 #include <a.out.h>
         and possibly #include <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 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 /etc/magic exists, it will be used
         together with other 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
         guage tests look for particular strings (cf.  #include <names.h>
         ) that can appear anywhere in the first few blocks of a file.  For exam-
         ple, 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 per-
         formed 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 encoding, 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 ':'.
    
                 '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 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 new-
                 line, 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 checking a list of files.  It is intended to be
                 used by programs that want filetype output from a pipe.
    
         -p, --preserve-date
                 On systems that support utime(2) or utimes(2), attempt to pre-
                 serve 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 pecu-
                 liar 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
    
    
    

    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 appro-
         priate.  The environment variable POSIXLY_CORRECT controls (on systems
         that support symbolic links), whether file will attempt to follow sym-
         links 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,) 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 compatible with the System V program of
         the same name.  This version knows more magic, however, so it will pro-
         duce 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 dif-
         fers 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
                         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 intro-
         duced 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 McMa-
         hon, 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, using an alternative magic file and internal
         logic.
    
         Altered by Eric Fischer (enf@pobox.com), July, 2000, to identify charac-
    
         The files tar.h and is_tar.c were written by John Gilmore from his pub-
         lic-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 sim-
         plistic, 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.
    
         If the file named by the file operand does not exist, cannot be read, or
         the type of the file named by the file operand cannot be determined, this
         is not be considered an error that affects the exit status.
    
    
    

    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
    
    
    

    BSD October 9, 2008 BSD

    
    
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