FILE(1)                    OpenBSD Reference Manual                    FILE(1)

NAME
     file - determine file type

SYNOPSIS
     file [-vczL] [-f namefile] [-m magicfiles] file [...]

DESCRIPTION
     This manual page documents version 3.22 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 ASCII 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 the file /etc/magic or
     the program itself, 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; 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 <sys/stat.h>.

     The magic number tests are used to check for files with data in particu-
     lar fixed formats.  The canonical example of this is a binary executable
     (compiled program) a.out file, whose format is defined in <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 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 in these
     files is read from the magic file /etc/magic.

     If an argument appears to be an ASCII file, file attempts to guess its
     language.  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) and determine whether an unknown file should be labelled as
     ``ASCII text'' or ``data''.

     The options are as follows:

     -v      Print the version of the program and exit.

     -m list
             Specify an alternate list of files containing magic numbers.

             This can be a single file, or a colon-separated list of files.

     -z      Try to look inside compressed files.

     -c      Cause a checking printout of the parsed form of the magic file.
             This is usually used in conjunction with -m to debug a new magic
             file before installing it.

     -f 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.

     -L      Cause symlinks to be followed, as the like-named option in ls(1).
             (on systems that support symbolic links).

ENVIRONMENT
     MAGIC   Default magic number files.

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 behaviour 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(1) com-
     mand 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 be-
     low) will collect additional or corrected magic file entries.  A consoli-
     dation 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 /etc/magic.orig).

HISTORY
     There has been a file command in every UNIX since at least Research Ver-
     sion 6 (man page dated January, 1975).  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 F. Darwin
     <ian@darwinisys.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.

     Altered by Rob McMahon <cudcv@warwick.ac.uk>, 1989, to extend the `&' op-
     erator from simple ``x&y != 0'' to ``x&y op z''.

     Altered by Guy Harris <guy@auspex.com>, 1993, to:

           put the ``old-style'' `&' operator back the way it was, because

                 1.   Rob McMahon's change broke the previous style of usage,

                 2.   The SunOS ``new-style'' `&' operator, which this version
                      of file supports, also handles ``x&y op z'',

                 3.   Rob's change wasn't documented in any case;

           put in multiple levels of `>';

           put in ``beshort'', ``leshort'', etc. keywords to look at numbers
           in the file in a specific byte order, rather than in the native
           byte order of the process running file.

     Currently maintained by Christos Zoulas <christos@zoulas.com>.

LEGAL NOTICE
     Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.  Covered by the
     standard Berkeley Software Distribution copyright; see the file LEGAL.NO-
     TICE in the distribution.

     The files tar.h and is_tar.c were written by John Gilmore from his pub-
     lic-domain tar program.

BUGS
     There must be a better way to automate the construction of the Magic file
     from all the glop in Magdir.  What is it?  Better yet, the magic file
     should be compiled into binary (say, ndbm(3) or, better yet, fixed-length
     ASCII strings for use in heterogenous network environments) for faster
     startup.  Then the program would run as fast as the Version 7 program of
     the same name, with the flexibility of the System V version.

     file uses several algorithms that favor speed over accuracy, thus it can
     be misled about the contents of ASCII files.

     The support for ASCII files (primarily for programming languages) is sim-
     plistic, inefficient and requires recompilation to update.

     There should be an ``else'' clause to follow a series of continuation
     lines.

     The magic file and keywords should have regular expression support.
     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.

     Another optimization would be to sort the magic file so that we can just
     run down all the tests for the first byte, first word, first long, etc,
     once we have fetched it.  Complain about conflicts in the magic file en-
     tries.  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.

     This manual page, and particularly this section, is too long.

AVAILABILITY
     You can obtain the original author's latest version by anonymous FTP on
     ftp.deshaw.com in the directory /pub/file/file-X.YY.tar.gz

OpenBSD 2.9                      July 30, 1997                               4
