FILE(1)                    OpenBSD Reference Manual                    FILE(1)

NAME
     file - determine file type

SYNOPSIS
     file [-0bCcehikLNnprsvz] [--help] [--mime-encoding] [--mime-type]
          [-F separator] [-f namefile] [-m magicfiles] file

DESCRIPTION
     The file utility 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
     modifying magic files or the program itself, make sure to preserve these
     keywords.  Users depend on knowing that all the readable files in a di-
     rectory 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, such as sockets, sym-
     bolic links, and named pipes (FIFOs), 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 exe-
     cutable, and which of several types thereof.  The concept of a ``magic''
     has been applied by extension to data files.  Any file with some invari-
     ant identifier at a small fixed offset into the file can usually be de-
     scribed in this way.  The information identifying these files is read
     from the magic file /etc/magic.  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 ex-
     amined 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 addi-
     tion, file will attempt to determine other characteristics of text-type
     files.  If the lines of a file are terminated by CR, CRLF, or NEL, in-
     stead 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 lan-
     guage 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
     -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.

     -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   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, --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.

     -h, --no-dereference
             Causes symlinks not to be followed.  This is the default if the
             environment variable POSIXLY_CORRECT is not defined.

     --help  Print a help message and exit.

     -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 also FILES, below.

     --mime-encoding, --mime-type
             Like -i, but print only the specified element(s).

     -k, --keep-going
             Don't stop at the first match, keep going.  Subsequent matches
             will have the string ``\012-'' prepended.  (If a newline is re-
             quired, see the -r option.)

     -L, --dereference
             Causes symlinks to be followed; analogous to the option of the
             same name in ls(1).  This is the default if the environment vari-
             able 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 on-
             ly 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 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 op-
             tion 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.

     The file utility exits 0 on success, and >0 if an error occurs.

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 whether file
     will attempt to follow symlinks or not.  If set, then file follows sym-
     links; otherwise it does not.  This is also controlled by the -L and -h
     options.

FILES
     /etc/magic  default list of magic numbers

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 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 whitespace as a delimiter, so that spaces in pat-
     tern 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

HISTORY
     There has been a file command in every UNIX since at least Research Ver-
     sion 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
     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, 1989.

     Guy Harris, made many changes from 1993 to the present.

     Primary development and maintenance from 1990 to the present by Christos
     Zoulas.

     Altered by Chris Lowth, 2000: Handle the -i option to output mime type
     strings, using an alternative magic file and internal logic.

     Altered by Eric Fischer, July, 2000, to identify character codes and at-
     tempt to identify the languages of non-ASCII files.

     Altered by Reuben Thomas, 2007 to 2008, to improve MIME support and merge
     MIME and non-MIME magic, support directories as well as files of magic,
     apply many bug fixes and improve the build system.

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

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.

OpenBSD 4.7                     January 2, 2010                              5
