479 lines
16 KiB
Groff
479 lines
16 KiB
Groff
.\" $NetBSD: file.1,v 1.17 2000/09/22 16:34:59 pooka Exp $
|
|
.\"
|
|
.TH FILE __CSECTION__ "Copyright but distributable"
|
|
.\" Id: file.man,v 1.36 2000/08/05 17:36:48 christos Exp
|
|
.SH NAME
|
|
file
|
|
\- determine file type
|
|
.SH SYNOPSIS
|
|
.B file
|
|
[
|
|
.B \-bciknsvzL
|
|
]
|
|
[
|
|
.B \-f
|
|
namefile ]
|
|
[
|
|
.B \-m
|
|
magicfiles ]
|
|
file ...
|
|
.SH DESCRIPTION
|
|
This manual page documents version 3.26 of the
|
|
.B file
|
|
command.
|
|
.PP
|
|
.B 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
|
|
.I first
|
|
test that succeeds causes the file type to be printed.
|
|
.PP
|
|
The type printed will usually contain one of the words
|
|
.B text
|
|
(the file contains only
|
|
printing characters and a few common control
|
|
characters and is probably safe to read on an
|
|
.SM ASCII
|
|
terminal),
|
|
.B executable
|
|
(the file contains the result of compiling a program
|
|
in a form understandable to some \s-1UNIX\s0 kernel or another),
|
|
or
|
|
.B 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
|
|
.I /usr/share/misc/magic
|
|
or the program itself,
|
|
.B "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''.
|
|
.PP
|
|
The filesystem tests are based on examining the return from a
|
|
.BR 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
|
|
.IR <sys/stat.h> .
|
|
.PP
|
|
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)
|
|
.I a.out
|
|
file, whose format is defined in
|
|
.I a.out.h
|
|
and possibly
|
|
.I 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 \s-1UNIX\s0 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 the magic file
|
|
.I /usr/share/misc/magic.
|
|
.PP
|
|
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,
|
|
.B 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.
|
|
.PP
|
|
Once
|
|
.B 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
|
|
.IR names.h )
|
|
that can appear anywhere in the first few blocks of a file.
|
|
For example, the keyword
|
|
.B .br
|
|
indicates that the file is most likely a
|
|
.BR troff (1)
|
|
input file, just as the keyword
|
|
.B 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
|
|
.BR tar (1)
|
|
archives).
|
|
.PP
|
|
Any file that cannot be identified as having been written
|
|
in any of the character sets listed above is simply said to be ``data''.
|
|
.SH OPTIONS
|
|
.TP 8
|
|
.B \-b
|
|
Do not prepend filenames to output lines (brief mode).
|
|
.TP 8
|
|
.B \-c
|
|
Cause a checking printout of the parsed form of the magic file.
|
|
This is usually used in conjunction with
|
|
.B \-m
|
|
to debug a new magic file before installing it.
|
|
.TP 8
|
|
.B \-f namefile
|
|
Read the names of the files to be examined from
|
|
.I namefile
|
|
(one per line)
|
|
before the argument list.
|
|
Either
|
|
.I namefile
|
|
or at least one filename argument must be present;
|
|
to test the standard input, use ``\-'' as a filename argument.
|
|
.TP 8
|
|
.B \-i
|
|
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 it's self (such as many of the
|
|
text file types, directories etc), and makes use of an alternative
|
|
``magic'' file.
|
|
(See ``FILES'' section, below).
|
|
.TP 8
|
|
.B \-k
|
|
Don't stop at the first match, keep going.
|
|
.TP 8
|
|
.B \-m list
|
|
Specify an alternate list of files containing magic numbers.
|
|
This can be a single file, or a colon-separated list of files.
|
|
.TP 8
|
|
.B \-n
|
|
Force stdout to be flushed after check a file. This is only useful if
|
|
checking a list of files. It is intended to be used by programs want
|
|
filetype output from a pipe.
|
|
.TP 8
|
|
.B \-v
|
|
Print the version of the program and exit.
|
|
.TP 8
|
|
.B \-z
|
|
Try to look inside compressed files.
|
|
.TP 8
|
|
.B \-L
|
|
option causes symlinks to be followed, as the like-named option in
|
|
.BR ls (1).
|
|
(on systems that support symbolic links).
|
|
.TP 8
|
|
.B \-s
|
|
Normally,
|
|
.B file
|
|
only attempts to read and determine the type of argument files which
|
|
.BR stat (2)
|
|
reports are ordinary files.
|
|
This prevents problems, because reading special files may have peculiar
|
|
consequences.
|
|
Specifying the
|
|
.BR \-s
|
|
option causes
|
|
.B 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
|
|
.B file
|
|
to disregard the file size as reported by
|
|
.BR stat (2)
|
|
since on some systems it reports a zero size for raw disk partitions.
|
|
.SH FILES
|
|
.I /usr/share/misc/magic
|
|
\- default list of magic numbers
|
|
.PP
|
|
.I __MAGIC__.mime
|
|
\- default list of magic numbers, used to output mime types when the -i option
|
|
is specified.
|
|
|
|
.SH ENVIRONMENT
|
|
The environment variable
|
|
.B MAGIC
|
|
can be used to set the default magic number files.
|
|
.SH SEE ALSO
|
|
.BR magic (1)
|
|
\- description of magic file format.
|
|
.br
|
|
.BR strings (1), " od" (1), " hexdump(1)"
|
|
\- tools for examining non-textfiles.
|
|
.SH 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.
|
|
.PP
|
|
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,
|
|
.br
|
|
>10 string language impress\ (imPRESS data)
|
|
.br
|
|
in an existing magic file would have to be changed to
|
|
.br
|
|
>10 string language\e impress (imPRESS data)
|
|
.br
|
|
In addition, in this version, if a pattern string contains a backslash,
|
|
it must be escaped. For example
|
|
.br
|
|
0 string \ebegindata Andrew Toolkit document
|
|
.br
|
|
in an existing magic file would have to be changed to
|
|
.br
|
|
0 string \e\ebegindata Andrew Toolkit document
|
|
.br
|
|
.PP
|
|
SunOS releases 3.2 and later from Sun Microsystems include a
|
|
.BR 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 `&' operator, used as,
|
|
for example,
|
|
.br
|
|
>16 long&0x7fffffff >0 not stripped
|
|
.SH 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.
|
|
.PP
|
|
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
|
|
.B file
|
|
command uses a magic file,
|
|
keep the old magic file around for comparison purposes
|
|
(rename it to
|
|
.IR /usr/share/misc/magic.orig ).
|
|
.SH EXAMPLES
|
|
.nf
|
|
$ 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
|
|
|
|
.fi
|
|
.SH HISTORY
|
|
There has been a
|
|
.B file
|
|
command in every \s-1UNIX\s0 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.
|
|
.PP
|
|
This program, based on the System V version,
|
|
was written by Ian Darwin without looking at anybody else's source code.
|
|
.PP
|
|
John Gilmore revised the code extensively, making it better than
|
|
the first version.
|
|
Geoff Collyer found several inadequacies
|
|
and provided some magic file entries.
|
|
The program has undergone continued evolution since.
|
|
.SH AUTHOR
|
|
Written by Ian F. Darwin, UUCP address {utzoo | ihnp4}!darwin!ian,
|
|
Internet address ian@sq.com,
|
|
postal address: P.O. Box 603, Station F, Toronto, Ontario, CANADA M4Y 2L8.
|
|
.PP
|
|
Altered by Rob McMahon, cudcv@warwick.ac.uk, 1989, to extend the `&' operator
|
|
from simple `x&y != 0' to `x&y op z'.
|
|
.PP
|
|
Altered by Guy Harris, guy@netapp.com, 1993, to:
|
|
.RS
|
|
.PP
|
|
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
|
|
.B file
|
|
supports, also handles `x&y op z', and 3) Rob's change wasn't documented
|
|
in any case;
|
|
.PP
|
|
put in multiple levels of `>';
|
|
.PP
|
|
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
|
|
.BR file .
|
|
.RE
|
|
.PP
|
|
Changes by Ian Darwin and various authors including
|
|
Christos Zoulas (christos@astron.com), 1990-1999.
|
|
.PP
|
|
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.
|
|
.PP
|
|
Altered by Eric Fischer (enf@pobox.com), July, 2000,
|
|
to identify character codes and attempt to identify the languages
|
|
of non-ASCII files.
|
|
.SH LEGAL NOTICE
|
|
Copyright (c) Ian F. Darwin, Toronto, Canada,
|
|
1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993.
|
|
.PP
|
|
This software is not subject to and may not be made subject to any
|
|
license of the American Telephone and Telegraph Company, Sun
|
|
Microsystems Inc., Digital Equipment Inc., Lotus Development Inc., the
|
|
Regents of the University of California, The X Consortium or MIT, or
|
|
The Free Software Foundation.
|
|
.PP
|
|
This software is not subject to any export provision of the United States
|
|
Department of Commerce, and may be exported to any country or planet.
|
|
.PP
|
|
Permission is granted to anyone to use this software for any purpose on
|
|
any computer system, and to alter it and redistribute it freely, subject
|
|
to the following restrictions:
|
|
.PP
|
|
1. The author is not responsible for the consequences of use of this
|
|
software, no matter how awful, even if they arise from flaws in it.
|
|
.PP
|
|
2. The origin of this software must not be misrepresented, either by
|
|
explicit claim or by omission. Since few users ever read sources,
|
|
credits must appear in the documentation.
|
|
.PP
|
|
3. Altered versions must be plainly marked as such, and must not be
|
|
misrepresented as being the original software. Since few users
|
|
ever read sources, credits must appear in the documentation.
|
|
.PP
|
|
4. This notice may not be removed or altered.
|
|
.\" .PP
|
|
.\" A few support files (\fIgetopt\fP, \fIstrtok\fP)
|
|
.\" distributed with this package
|
|
.\" are by Henry Spencer and are subject to the same terms as above.
|
|
.\" .PP
|
|
.\" A few simple support files (\fIstrtol\fP, \fIstrchr\fP)
|
|
.\" distributed with this package
|
|
.\" are in the public domain; they are so marked.
|
|
.\"
|
|
.\" enf: commented out because these support files don't seem to be included
|
|
.PP
|
|
The files
|
|
.I tar.h
|
|
and
|
|
.I is_tar.c
|
|
were written by John Gilmore from his public-domain
|
|
.B tar
|
|
program, and are not covered by the above restrictions.
|
|
.SH 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,
|
|
.BR ndbm (3)
|
|
or, better yet, fixed-length
|
|
.SM 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.
|
|
.PP
|
|
.B File
|
|
uses several algorithms that favor speed over accuracy,
|
|
thus it can be misled about the contents of
|
|
text
|
|
files.
|
|
.PP
|
|
The support for
|
|
text
|
|
files (primarily for programming languages)
|
|
is simplistic, inefficient and requires recompilation to update.
|
|
.PP
|
|
There should be an ``else'' clause to follow a series of continuation lines.
|
|
.PP
|
|
The magic file and keywords should have regular expression support.
|
|
Their use of
|
|
.SM "ASCII TAB"
|
|
as a field delimiter is ugly and makes
|
|
it hard to edit the files, but is entrenched.
|
|
.PP
|
|
It might be advisable to allow upper-case letters in keywords
|
|
for e.g.,
|
|
.BR troff (1)
|
|
commands vs man page macros.
|
|
Regular expression support would make this easy.
|
|
.PP
|
|
The program doesn't grok \s-2FORTRAN\s0.
|
|
It should be able to figure \s-2FORTRAN\s0 by seeing some keywords which
|
|
appear indented at the start of line.
|
|
Regular expression support would make this easy.
|
|
.PP
|
|
The list of keywords in
|
|
.I ascmagic
|
|
probably belongs in the Magic file.
|
|
This could be done by using some keyword like `*' for the offset value.
|
|
.PP
|
|
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?
|
|
.PP
|
|
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.
|
|
.PP
|
|
This program is slower than some vendors' file commands.
|
|
The new support for multiple character codes makes it even slower.
|
|
.PP
|
|
This manual page, and particularly this section, is too long.
|
|
.SH AVAILABILITY
|
|
You can obtain the original author's latest version by anonymous FTP
|
|
on
|
|
.B ftp.astron.com
|
|
in the directory
|
|
.I /pub/file/file-X.YY.tar.gz
|