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FILE
!!!FILE
NAME
SYNOPSIS
DESCRIPTION
OPTIONS
FILES
ENVIRONMENT
SEE ALSO
STANDARDS CONFORMANCE
MAGIC DIRECTORY
EXAMPLES
HISTORY
LEGAL NOTICE
BUGS
AVAILABILITY
----
!!NAME


file - determine file type
!!SYNOPSIS


__file__ [[ __-bciknsvzL__ ] [[ __-f__
''namefile'' ] [[ __-m__ ''magicfiles'' ]
''file'' ...__
file -C__ [[ __-m__ magicfile ]
!!DESCRIPTION


This manual page documents version 3.37-3.1 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 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'', __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 and
change ``shell commands text'' to ``shell script''. Note
that the file ''/usr/share/misc/magic'' is built
mechanically from a large number of small files in the
subdirectory ''Magdir'' in the source distribution of
this program.


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
''''.


The magic number 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 ''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 `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
''/etc/magic'' and the compiled magic file
''/usr/share/misc/magic.mgc ,'' or
''/usr/share/misc/magic'' if the compile file does not
exist.


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).


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.


''-c, --checking-printout''


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.


''-C, --compile''


Write a magic.mgc output file that contains a pre-parsed
version of file.


''-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.


''-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 recognised by the command itself (such
as many of the text file types, directories etc), and makes
use of an alternative ``magic'' file. (See ``FILES''
section, below).


''-k, --keep-going''


Don't stop at the first match, keep going.


''-m, --magic-file list''


Specify an alternate list of files containing magic numbers.
This can be a single file, or a colon-separated list of
files.


''-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.


__-v__


Print the version of the program and exit.


''-z, --uncompress''


Try to look inside compressed files.


''-L, --dereference''


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


''-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.


''--help''


Print a help message and exit.


''--version''


Print version information and exit.
!!FILES


''/usr/share/misc/magic.mgc''


Default compiled list of magic numbers


''/usr/share/misc/magic''


Default list of magic numbers


''/usr/share/misc/magic.mime''


Default list of magic numbers, used to output mime types
when the -i option is specified.


''/etc/magic''


Local additions to magic wisdom.
!!ENVIRONMENT


The environment variable __MAGIC__ can be used to set the
default magic number files.
!!SEE ALSO


magic(5) - description of magic file format.__
strings__(1), od(1), __hexdump(1)__ - tools for
examining non-textfiles.
!!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
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,
in an existing magic file would have to be changed to
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) command 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 `
__
__
!!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.
!!EXAMPLES


$ file file.c file /dev/hda
file.c:   C program text
file:     ELF 32-bit LSB executable, Intel 80386, version 1,
dynamically linked, not stripped
/dev/hda: block special
$ 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/hda
file.c:      text/x-c
file:        application/x-executable, dynamically linked (uses shared libs), not stripped
/dev/hda:    application/x-not-regular-file
!!HISTORY


There has been a __file__ command in every
UNIX since at least Research Version 6 (man
page dated January 16, 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 Darwin


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 `


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 and 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.


The list of contributors to the
!!LEGAL NOTICE


Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.
Covered by the standard Berkeley Software Distribution
copyright; see the file LEGAL.NOTICE in the source
distribution.


The files ''tar.h'' and ''is_tar.c'' were written by
John Gilmore from his public-domain __tar__ 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?
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 text
files.


The support for text files (primarily for programming
languages) is simplistic, 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 optimisation 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 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.
``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. The
new support for multiple character codes makes it even
slower.


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.astron.com__ in the directory
''/pub/file/file-X.YY.tar.gz''


This __Debian__ version adds long options and corrects
some bugs. It can be obtained from every site carrying a
__Debian__ distribution (ftp.debian.org and
mirrors).
----
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Last edited on Tuesday, June 4, 2002 12:22:00 am by "perry"
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