Provided by: file_5.37-5_amd64 bug

NAME

     file — determine file type

SYNOPSIS

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

DESCRIPTION

     This manual page documents version 5.37 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 adding local definitions to
     /etc/magic, 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” 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/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 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

     --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 flag 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.

             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’.

     --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
             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
             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
                   indir        15         recursion limit for indirect magic
                   name         30         use count limit for name/use magic
                   elf_notes    256        max ELF notes processed
                   elf_phnum    128        max ELF program sections processed
                   elf_shnum    32768      max ELF sections processed
                   regex        8192       length limit for regex searches
                   bytes        1048576    max number of bytes to read from file

     -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 flag disables sandboxing which is enabled by default.  This option is needed
             for file to execute external descompressing programs, i.e. when the -z flag is
             specified and the built-in decompressors are not available.

             Note: This Debian version of file was built without seccomp support, so 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

     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

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

EXIT STATUS

     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

           $ 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

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

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.  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

     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 flag.

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.

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 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

     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

     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

     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 move around the file.  One
     must be careful though because this has performance (and thus security considerations).

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.