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-.TH FILE __CSECTION__ "Copyright but distributable"
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-.\" $Id: file.man,v 1.27 1996/06/22 22:05:07 christos Exp $
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-.SH NAME
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-file
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-\- determine file type
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-.SH SYNOPSIS
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-.B file
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-[
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-.B \-vczL
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-]
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-[
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-.B \-f
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-namefile ]
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-[
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-.B \-m
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-magicfiles ]
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-file ...
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-.SH DESCRIPTION
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-This manual page documents version __VERSION__ of the
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-.B file
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-command.
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-.B File
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-tests each argument in an attempt to classify it.
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-There are three sets of tests, performed in this order:
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-filesystem tests, magic number tests, and language tests.
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-The
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-.I first
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-test that succeeds causes the file type to be printed.
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-.PP
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-The type printed will usually contain one of the words
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-.B text
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-(the file contains only
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-.SM ASCII
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-characters and is probably safe to read on an
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-.SM ASCII
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-terminal),
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-.B executable
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-(the file contains the result of compiling a program
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-in a form understandable to some \s-1UNIX\s0 kernel or another),
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-or
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-.B data
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-meaning anything else (data is usually `binary' or non-printable).
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-Exceptions are well-known file formats (core files, tar archives)
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-that are known to contain binary data.
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-When modifying the file
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-.I __MAGIC__
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-or the program itself,
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-.B "preserve these keywords" .
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-People depend on knowing that all the readable files in a directory
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-have the word ``text'' printed.
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-Don't do as Berkeley did \- change ``shell commands text''
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-to ``shell script''.
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-.PP
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-The filesystem tests are based on examining the return from a
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-.BR stat (2)
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-system call.
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-The program checks to see if the file is empty,
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-or if it's some sort of special file.
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-Any known file types appropriate to the system you are running on
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-(sockets, symbolic links, or named pipes (FIFOs) on those systems that
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-implement them)
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-are intuited if they are defined in
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-the system header file
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-.IR sys/stat.h .
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-.PP
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-The magic number tests are used to check for files with data in
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-particular fixed formats.
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-The canonical example of this is a binary executable (compiled program)
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-.I a.out
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-file, whose format is defined in
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-.I a.out.h
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-and possibly
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-.I exec.h
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-in the standard include directory.
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-These files have a `magic number' stored in a particular place
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-near the beginning of the file that tells the \s-1UNIX\s0 operating system
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-that the file is a binary executable, and which of several types thereof.
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-The concept of `magic number' has been applied by extension to data files.
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-Any file with some invariant identifier at a small fixed
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-offset into the file can usually be described in this way.
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-The information in these files is read from the magic file
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-.I __MAGIC__.
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-.PP
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-If an argument appears to be an
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-.SM ASCII
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-file,
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-.B file
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-attempts to guess its language.
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-The language tests look for particular strings (cf
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-.IR names.h )
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-that can appear anywhere in the first few blocks of a file.
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-For example, the keyword
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-.B .br
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-indicates that the file is most likely a
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-.BR troff (1)
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-input file, just as the keyword
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-.B struct
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-indicates a C program.
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-These tests are less reliable than the previous
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-two groups, so they are performed last.
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-The language test routines also test for some miscellany
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-(such as
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-.BR tar (1)
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-archives) and determine whether an unknown file should be
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-labelled as `ascii text' or `data'.
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-.SH OPTIONS
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-.TP 8
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-.B \-v
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-Print the version of the program and exit.
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-.TP 8
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-.B \-m list
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-Specify an alternate list of files containing magic numbers.
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-This can be a single file, or a colon-separated list of files.
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-.TP 8
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-.B \-z
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-Try to look inside compressed files.
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-.TP 8
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-.B \-c
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-Cause a checking printout of the parsed form of the magic file.
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-This is usually used in conjunction with
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-.B \-m
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-to debug a new magic file before installing it.
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-.TP 8
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-.B \-f namefile
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-Read the names of the files to be examined from
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-.I namefile
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-(one per line)
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-before the argument list.
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-Either
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-.I namefile
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-or at least one filename argument must be present;
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-to test the standard input, use ``-'' as a filename argument.
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-.TP 8
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-.B \-L
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-option causes symlinks to be followed, as the like-named option in
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-.BR ls (1).
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-(on systems that support symbolic links).
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-.SH FILES
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-.I __MAGIC__
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-\- default list of magic numbers
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-.SH ENVIRONMENT
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-The environment variable
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-.B MAGIC
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-can be used to set the default magic number files.
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-.SH SEE ALSO
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-.BR magic (__FSECTION__)
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-\- description of magic file format.
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-.br
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-.BR strings (1), " od" (1)
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-\- tools for examining non-textfiles.
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-.SH STANDARDS CONFORMANCE
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-This program is believed to exceed the System V Interface Definition
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-of FILE(CMD), as near as one can determine from the vague language
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-contained therein.
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-Its behaviour is mostly compatible with the System V program of the same name.
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-This version knows more magic, however, so it will produce
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-different (albeit more accurate) output in many cases.
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-.PP
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-The one significant difference
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-between this version and System V
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-is that this version treats any white space
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-as a delimiter, so that spaces in pattern strings must be escaped.
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-For example,
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-.br
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->10 string language impress\ (imPRESS data)
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-.br
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-in an existing magic file would have to be changed to
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-.br
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->10 string language\e impress (imPRESS data)
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-.br
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-In addition, in this version, if a pattern string contains a backslash,
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-it must be escaped. For example
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-.br
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-0 string \ebegindata Andrew Toolkit document
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-.br
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-in an existing magic file would have to be changed to
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-.br
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-0 string \e\ebegindata Andrew Toolkit document
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-.br
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-.PP
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-SunOS releases 3.2 and later from Sun Microsystems include a
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-.BR file (1)
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-command derived from the System V one, but with some extensions.
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-My version differs from Sun's only in minor ways.
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-It includes the extension of the `&' operator, used as,
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-for example,
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-.br
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->16 long&0x7fffffff >0 not stripped
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-.SH MAGIC DIRECTORY
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-The magic file entries have been collected from various sources,
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-mainly USENET, and contributed by various authors.
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-Christos Zoulas (address below) will collect additional
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-or corrected magic file entries.
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-A consolidation of magic file entries
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-will be distributed periodically.
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-.PP
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-The order of entries in the magic file is significant.
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-Depending on what system you are using, the order that
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-they are put together may be incorrect.
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-If your old
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-.B file
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-command uses a magic file,
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-keep the old magic file around for comparison purposes
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-(rename it to
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-.IR __MAGIC__.orig ).
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-.SH HISTORY
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-There has been a
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-.B file
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-command in every \s-1UNIX\s0 since at least Research Version 6
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-(man page dated January, 1975).
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-The System V version introduced one significant major change:
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-the external list of magic number types.
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-This slowed the program down slightly but made it a lot more flexible.
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-.PP
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-This program, based on the System V version,
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-was written by Ian Darwin without looking at anybody else's source code.
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-.PP
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-John Gilmore revised the code extensively, making it better than
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-the first version.
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-Geoff Collyer found several inadequacies
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-and provided some magic file entries.
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-The program has undergone continued evolution since.
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-.SH AUTHOR
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-Written by Ian F. Darwin, UUCP address {utzoo | ihnp4}!darwin!ian,
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-Internet address ian@sq.com,
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-postal address: P.O. Box 603, Station F, Toronto, Ontario, CANADA M4Y 2L8.
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-.PP
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-Altered by Rob McMahon, cudcv@warwick.ac.uk, 1989, to extend the `&' operator
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-from simple `x&y != 0' to `x&y op z'.
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-.PP
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-Altered by Guy Harris, guy@auspex.com, 1993, to:
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-.RS
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-.PP
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-put the ``old-style'' `&'
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-operator back the way it was, because 1) Rob McMahon's change broke the
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-previous style of usage, 2) the SunOS ``new-style'' `&' operator,
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-which this version of
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-.B file
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-supports, also handles `x&y op z', and 3) Rob's change wasn't documented
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-in any case;
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-.PP
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-put in multiple levels of `>';
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-.PP
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-put in ``beshort'', ``leshort'', etc. keywords to look at numbers in the
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-file in a specific byte order, rather than in the native byte order of
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-the process running
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-.BR file .
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-.RE
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-.PP
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-Changes by Ian Darwin and various authors including
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-Christos Zoulas (christos@ee.cornell.edu), 1990-1992.
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-.SH LEGAL NOTICE
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-Copyright (c) Ian F. Darwin, Toronto, Canada,
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-1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993.
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-.PP
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-This software is not subject to and may not be made subject to any
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-license of the American Telephone and Telegraph Company, Sun
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-Microsystems Inc., Digital Equipment Inc., Lotus Development Inc., the
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-Regents of the University of California, The X Consortium or MIT, or
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-The Free Software Foundation.
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-.PP
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-This software is not subject to any export provision of the United States
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-Department of Commerce, and may be exported to any country or planet.
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-.PP
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-Permission is granted to anyone to use this software for any purpose on
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-any computer system, and to alter it and redistribute it freely, subject
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-to the following restrictions:
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-.PP
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-1. The author is not responsible for the consequences of use of this
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-software, no matter how awful, even if they arise from flaws in it.
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-.PP
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-2. The origin of this software must not be misrepresented, either by
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-explicit claim or by omission. Since few users ever read sources,
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-credits must appear in the documentation.
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-.PP
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-3. Altered versions must be plainly marked as such, and must not be
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-misrepresented as being the original software. Since few users
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-ever read sources, credits must appear in the documentation.
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-.PP
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-4. This notice may not be removed or altered.
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-.PP
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-A few support files (\fIgetopt\fP, \fIstrtok\fP)
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-distributed with this package
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-are by Henry Spencer and are subject to the same terms as above.
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-.PP
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-A few simple support files (\fIstrtol\fP, \fIstrchr\fP)
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-distributed with this package
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-are in the public domain; they are so marked.
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-.PP
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-The files
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-.I tar.h
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-and
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-.I is_tar.c
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-were written by John Gilmore from his public-domain
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-.B tar
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-program, and are not covered by the above restrictions.
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-.SH BUGS
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-There must be a better way to automate the construction of the Magic
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-file from all the glop in Magdir. What is it?
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-Better yet, the magic file should be compiled into binary (say,
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-.BR ndbm (3)
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-or, better yet, fixed-length
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-.SM ASCII
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-strings for use in heterogenous network environments) for faster startup.
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-Then the program would run as fast as the Version 7 program of the same name,
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-with the flexibility of the System V version.
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-.PP
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-.B File
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-uses several algorithms that favor speed over accuracy,
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-thus it can be misled about the contents of
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-.SM ASCII
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-files.
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-.PP
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-The support for
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-.SM ASCII
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-files (primarily for programming languages)
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-is simplistic, inefficient and requires recompilation to update.
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-.PP
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-There should be an ``else'' clause to follow a series of continuation lines.
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-.PP
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-The magic file and keywords should have regular expression support.
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-Their use of
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-.SM "ASCII TAB"
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-as a field delimiter is ugly and makes
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-it hard to edit the files, but is entrenched.
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-.PP
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-It might be advisable to allow upper-case letters in keywords
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-for e.g.,
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-.BR troff (1)
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-commands vs man page macros.
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-Regular expression support would make this easy.
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-.PP
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-The program doesn't grok \s-2FORTRAN\s0.
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-It should be able to figure \s-2FORTRAN\s0 by seeing some keywords which
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-appear indented at the start of line.
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-Regular expression support would make this easy.
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-.PP
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-The list of keywords in
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-.I ascmagic
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-probably belongs in the Magic file.
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-This could be done by using some keyword like `*' for the offset value.
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-.PP
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-Another optimisation would be to sort
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-the magic file so that we can just run down all the
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-tests for the first byte, first word, first long, etc, once we
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-have fetched it. Complain about conflicts in the magic file entries.
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-Make a rule that the magic entries sort based on file offset rather
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-than position within the magic file?
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-.PP
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-The program should provide a way to give an estimate
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-of ``how good'' a guess is.
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-We end up removing guesses (e.g. ``From '' as first 5 chars of file) because
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-they are not as good as other guesses (e.g. ``Newsgroups:'' versus
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-"Return-Path:"). Still, if the others don't pan out, it should be
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-possible to use the first guess.
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-.PP
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-This program is slower than some vendors' file commands.
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-.PP
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-This manual page, and particularly this section, is too long.
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-.SH AVAILABILITY
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-You can obtain the original author's latest version by anonymous FTP
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-on
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-.B tesla.ee.cornell.edu
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-in the directory
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-.I /pub/file-X.YY.tar.gz
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