file(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | FILES | EXIT STATUS | EXAMPLES | SEE ALSO | STANDARDS CONFORMANCE | SECURITY | MAGIC DIRECTORY | HISTORY | LEGAL NOTICE | BUGS | TODO | AVAILABILITY | COLOPHON

FILE(1)                BSD General Commands Manual               FILE(1)

NAME         top

     file — determine file type

SYNOPSIS         top

     file [-bcdEhiklLNnprsSvzZ0] [--apple] [--exclude-quiet]
          [--extension] [--mime-encoding] [--mime-type] [-e testname]
          [-F separator] [-f namefile] [-m magicfiles] [-P name=value]
          file ...
     file -C [-m magicfiles]
     file [--help]

DESCRIPTION         top

     This manual page documents version 5.40 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 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 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 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 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 the compiled magic file /usr/local/share/misc/magic.mgc,
     or the files in the directory /usr/local/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 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, JSON
     files).

     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         top

     --apple
             Causes the file command to output the file type and creator
             code as used by older MacOS versions.  The code consists of
             eight letters, the first describing the file type, the
             latter the creator.  This option works properly only for
             file formats that have the apple-style output defined.

     -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
             option to debug a new magic file before installing it.

     -d      Prints internal debugging information to stderr.

     -E      On filesystem errors (file not found etc), instead of
             handling the error as regular output as POSIX mandates and
             keep going, issue an error message and exit.

     -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).

             ascii     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    Ignored for backwards compatibility.

             cdf       Prints details of Compound Document Files.

             compress  Checks for, and looks inside, compressed files.

             csv       Checks Comma Separated Value files.

             elf       Prints ELF file details, provided soft magic
                       tests are enabled and the elf magic is found.

             json      Examines JSON (RFC-7159) files by parsing them
                       for compliance.

             soft      Consults magic files.

             tar       Examines tar files by verifying the checksum of
                       the 512 byte tar header.  Excluding this test can
                       provide more detailed content description by
                       using the soft magic method.

             text      A synonym for ‘ascii’.

     --exclude-quiet
             Like --exclude but ignore tests that file does not know
             about.  This is intended for compatibility with older
             versions of file.

     --extension
             Print a slash-separated list of valid extensions for the
             file type found.

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

     -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.  Please
             note that namefile is unwrapped and the enclosed filenames
             are processed when this option is encountered and before
             any further options processing is done.  This allows one to
             process multiple lists of files with different command line
             arguments on the same file invocation.  Thus if you want to
             set the delimiter, you need to do it before you specify the
             list of files, like: “-F @ -f namefile”, instead of: “-f
             namefile -F @”.

     -h, --no-dereference
             This 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”.

     --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 newline, see the -r option.)  The magic pattern
             with the highest strength (see the -l option) comes first.

     -l, --list
             Shows a list of patterns and their strength sorted
             descending by magic(4) strength which is used for the
             matching (see also the -k option).

     -L, --dereference
             This 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(3) or utimes(2), attempt to
             preserve the access time of files analyzed, to pretend that
             file never read them.

     -P, --parameter name=value
             Set various parameter limits.

                   Name         Default    Explanation
                   bytes        1048576    max number of bytes to read
                                                                          from
                                                                          file
                   elf_notes    256        max ELF notes processed
                   elf_phnum    2048       max ELF program sections
                                                                          processed
                   elf_shnum    32768      max ELF sections processed
                   encoding     65536      max number of bytes to scan
                                                                          for
                                                                          encoding
                                                                          evaluation
                   indir        50         recursion limit for indirect
                                                                          magic
                   name         50         use count limit for name/use
                                                                          magic
                   regex        8192       length limit for regex
                                                                          searches

     -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.

     -S, --no-sandbox
             On systems where libseccomp
             (https://github.com/seccomp/libseccomp ) is available, the
             -S option disables sandboxing which is enabled by default.
             This option is needed for file to execute external
             decompressing programs, i.e. when the -z option is
             specified and the built-in decompressors are not available.
             On systems where sandboxing is not available, this option
             has no effect.

     -v, --version
             Print the version of the program and exit.

     -z, --uncompress
             Try to look inside compressed files.

     -Z, --uncompress-noreport
             Try to look inside compressed files, but report information
             about the contents only not the compression.

     -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.

             If this option is repeated more than once, then file prints
             just the filename followed by a NUL followed by the
             description (or ERROR: text) followed by a second NUL for
             each entry.

     --help  Print a help message and exit.

ENVIRONMENT         top

     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 appropriate.  The environment variable POSIXLY_CORRECT controls
     (on systems that support symbolic links), whether 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.

FILES         top

     /usr/local/share/misc/magic.mgc  Default compiled list of magic.
     /usr/local/share/misc/magic      Directory containing default magic
                                      files.

EXIT STATUS         top

     file will exit with 0 if the operation was successful or >0 if an
     error was encountered.  The following errors cause diagnostic
     messages, but don't affect the program exit code (as POSIX
     requires), unless -E is specified:
           A file cannot be found
           There is no permission to read a file
           The file type cannot be determined

EXAMPLES         top

           $ 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
           /dev/hda:    application/x-not-regular-file
           /dev/wd0a:   application/x-not-regular-file

SEE ALSO         top

     hexdump(1), od(1), strings(1), magic(4)

STANDARDS CONFORMANCE         top

     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.
     This 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

SECURITY         top

     On systems where libseccomp (https://github.com/seccomp/libseccomp )
     is available, file is enforces limiting system calls to only the
     ones necessary for the operation of the program.  This enforcement
     does not provide any security benefit when file is asked to
     decompress input files running external programs with the -z
     option.  To enable execution of external decompressors, one needs
     to disable sandboxing using the -S option.

MAGIC DIRECTORY         top

     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/local/share/misc/magic.orig).

HISTORY         top

     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
     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 of 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, 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.

     Altered by Reuben Thomas ⟨rrt@sc3d.org⟩, 2007-2011, to improve MIME
     support, merge MIME and non-MIME magic, support directories as well
     as files of magic, apply many bug fixes, update and fix a lot of
     magic, improve the build system, improve the documentation, and
     rewrite the Python bindings in pure Python.

     The list of contributors to the ‘magic’ directory (magic files) is
     too long to include here.  You know who you are; thank you.  Many
     contributors are listed in the source files.

LEGAL NOTICE         top

     Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.  Covered
     by the standard Berkeley Software Distribution copyright; see the
     file COPYING 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         top

     Please report bugs and send patches to the bug tracker at
     https://bugs.astron.com/  or the mailing list at ⟨file@astron.com⟩
     (visit https://mailman.astron.com/mailman/listinfo/file  first to
     subscribe).

TODO         top

     Fix output so that tests for MIME and APPLE flags are not needed
     all over the place, and actual output is only done in one place.
     This needs a design.  Suggestion: push possible outputs on to a
     list, then pick the last-pushed (most specific, one hopes) value at
     the end, or use a default if the list is empty.  This should not
     slow down evaluation.

     The handling of MAGIC_CONTINUE and printing \012- between entries
     is clumsy and complicated; refactor and centralize.

     Some of the encoding logic is hard-coded in encoding.c and can be
     moved to the magic files if we had a !:charset annotation.

     Continue to squash all magic bugs.  See Debian BTS for a good
     source.

     Store arbitrarily long strings, for example for %s patterns, so
     that they can be printed out.  Fixes Debian bug #271672.  This can
     be done by allocating strings in a string pool, storing the string
     pool at the end of the magic file and converting all the string
     pointers to relative offsets from the string pool.

     Add syntax for relative offsets after current level (Debian bug
     #466037).

     Make file -ki work, i.e. give multiple MIME types.

     Add a zip library so we can peek inside Office2007 documents to
     print more details about their contents.

     Add an option to print URLs for the sources of the file
     descriptions.

     Combine script searches and add a way to map executable names to
     MIME types (e.g. have a magic value for !:mime which causes the
     resulting string to be looked up in a table).  This would avoid
     adding the same magic repeatedly for each new hash-bang
     interpreter.

     When a file descriptor is available, we can skip and adjust the
     buffer instead of the hacky buffer management we do now.

     Fix “name” and “use” to check for consistency at compile time
     (duplicate “name”, “use” pointing to undefined “name” ).  Make
     “name” / “use” more efficient by keeping a sorted list of names.
     Special-case ^ to flip endianness in the parser so that it does not
     have to be escaped, and document it.

     If the offsets specified internally in the file exceed the buffer
     size ( HOWMANY variable in file.h), then we don't seek to that
     offset, but we give up.  It would be better if buffer managements
     was done when the file descriptor is available so we can seek
     around the file.  One must be careful though because this has
     performance and thus security considerations, because one can slow
     down things by repeateadly seeking.

     There is support now for keeping separate buffers and having
     offsets from the end of the file, but the internal buffer
     management still needs an overhaul.

AVAILABILITY         top

     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.

COLOPHON         top

     This page is part of the file (a file type guesser) project.
     Information about the project can be found at
     http://www.darwinsys.com/file/.  If you have a bug report for this
     manual page, see ⟨http://bugs.gw.com/my_view_page.php⟩.  This page
     was obtained from the project's upstream Git read-only mirror of
     the CVS repository ⟨https://github.com/glensc/file⟩ on 2021-04-01.
     (At that time, the date of the most recent commit that was found in
     the repository was 2021-04-01.)  If you discover any rendering
     problems in this HTML version of the page, or you believe there is
     a better or more up-to-date source for the page, or you have
     corrections or improvements to the information in this COLOPHON
     (which is not part of the original manual page), send a mail to
     man-pages@man7.org

BSD                         February 5, 2021                         BSD

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