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.\" $File: magic.man,v 1.71 2011/12/07 11:58:24 rrt Exp $
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2011-10-06 06:01:12 +00:00
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.Dd April 20, 2011
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2008-01-13 20:35:16 +00:00
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.Dt MAGIC __FSECTION__
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.Os
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2009-01-02 02:57:16 +00:00
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.\" install as magic.4 on USG, magic.5 on V7, Berkeley and Linux systems.
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.Sh NAME
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.Nm magic
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.Nd file command's magic pattern file
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.Sh DESCRIPTION
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1997-03-18 18:00:03 +00:00
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This manual page documents the format of the magic file as
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used by the
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.Xr file __CSECTION__
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2003-02-28 05:19:36 +00:00
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command, version __VERSION__.
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The
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.Xr file __CSECTION__
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1994-09-03 19:16:28 +00:00
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command identifies the type of a file using,
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among other tests,
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2009-01-02 02:57:16 +00:00
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a test for whether the file contains certain
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.Dq "magic patterns" .
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1994-09-03 19:16:28 +00:00
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The file
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.Pa __MAGIC__
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specifies what patterns are to be tested for, what message or
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MIME type to print if a particular pattern is found,
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1994-09-03 19:16:28 +00:00
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and additional information to extract from the file.
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.Pp
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1994-09-03 19:16:28 +00:00
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Each line of the file specifies a test to be performed.
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A test compares the data starting at a particular offset
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in the file with a byte value, a string or a numeric value.
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If the test succeeds, a message is printed.
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1994-09-03 19:16:28 +00:00
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The line consists of the following fields:
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.Bl -tag -width ".Dv message"
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.It Dv offset
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1994-09-03 19:16:28 +00:00
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A number specifying the offset, in bytes, into the file of the data
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which is to be tested.
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.It Dv type
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The type of the data to be tested.
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The possible values are:
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.Bl -tag -width ".Dv lestring16"
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.It Dv byte
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A one-byte value.
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.It Dv short
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A two-byte value in this machine's native byte order.
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.It Dv long
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A four-byte value in this machine's native byte order.
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.It Dv quad
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An eight-byte value in this machine's native byte order.
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.It Dv float
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A 32-bit single precision IEEE floating point number in this machine's native byte order.
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.It Dv double
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A 64-bit double precision IEEE floating point number in this machine's native byte order.
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.It Dv string
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A string of bytes.
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The string type specification can be optionally followed
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by /[WwcCtb]*.
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The
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.Dq W
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flag compacts whitespace in the target, which must
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contain at least one whitespace character.
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If the magic has
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.Dv n
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consecutive blanks, the target needs at least
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.Dv n
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consecutive blanks to match.
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The
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.Dq w
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flag treats every blank in the magic as an optional blank.
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The
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.Dq c
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flag specifies case insensitive matching: lower case
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characters in the magic match both lower and upper case characters in the
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target, whereas upper case characters in the magic only match upper case
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characters in the target.
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The
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.Dq C
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flag specifies case insensitive matching: upper case
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characters in the magic match both lower and upper case characters in the
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target, whereas lower case characters in the magic only match upper case
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characters in the target.
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To do a complete case insensitive match, specify both
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.Dq c
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and
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.Dq C .
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The
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.Dq t
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flag forces the test to be done for text files, while the
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.Dq b
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flag forces the test to be done for binary files.
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.It Dv pstring
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A Pascal-style string where the first byte/short/int is interpreted as the an
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unsigned length.
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The length defaults to byte and can be specified as a modifier.
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The following modifiers are supported:
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.Bl -tag -compact -width B
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.It B
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A byte length (default).
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.It H
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A 2 byte big endian length.
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.It h
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A 2 byte big little length.
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.It L
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A 4 byte big endian length.
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.It l
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A 4 byte big little length.
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.It J
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The length includes itself in its count.
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.El
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The string is not NUL terminated.
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.Dq J
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is used rather than the more
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valuable
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.Dq I
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because this type of length is a feature of the JPEG
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format.
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.It Dv date
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A four-byte value interpreted as a UNIX date.
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.It Dv qdate
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A eight-byte value interpreted as a UNIX date.
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.It Dv ldate
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2001-10-08 22:50:54 +00:00
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A four-byte value interpreted as a UNIX-style date, but interpreted as
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local time rather than UTC.
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.It Dv qldate
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An eight-byte value interpreted as a UNIX-style date, but interpreted as
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local time rather than UTC.
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.It Dv beid3
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A 32-bit ID3 length in big-endian byte order.
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.It Dv beshort
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A two-byte value in big-endian byte order.
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.It Dv belong
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A four-byte value in big-endian byte order.
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.It Dv bequad
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An eight-byte value in big-endian byte order.
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.It Dv befloat
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A 32-bit single precision IEEE floating point number in big-endian byte order.
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.It Dv bedouble
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A 64-bit double precision IEEE floating point number in big-endian byte order.
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.It Dv bedate
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A four-byte value in big-endian byte order,
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interpreted as a Unix date.
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.It Dv beqdate
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An eight-byte value in big-endian byte order,
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interpreted as a Unix date.
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.It Dv beldate
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A four-byte value in big-endian byte order,
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interpreted as a UNIX-style date, but interpreted as local time rather
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than UTC.
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.It Dv beqldate
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An eight-byte value in big-endian byte order,
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interpreted as a UNIX-style date, but interpreted as local time rather
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than UTC.
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.It Dv bestring16
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A two-byte unicode (UCS16) string in big-endian byte order.
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.It Dv leid3
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A 32-bit ID3 length in little-endian byte order.
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.It Dv leshort
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A two-byte value in little-endian byte order.
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.It Dv lelong
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A four-byte value in little-endian byte order.
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.It Dv lequad
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An eight-byte value in little-endian byte order.
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.It Dv lefloat
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A 32-bit single precision IEEE floating point number in little-endian byte order.
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.It Dv ledouble
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A 64-bit double precision IEEE floating point number in little-endian byte order.
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.It Dv ledate
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A four-byte value in little-endian byte order,
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interpreted as a UNIX date.
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.It Dv leqdate
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An eight-byte value in little-endian byte order,
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interpreted as a UNIX date.
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.It Dv leldate
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A four-byte value in little-endian byte order,
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interpreted as a UNIX-style date, but interpreted as local time rather
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than UTC.
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.It Dv leqldate
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An eight-byte value in little-endian byte order,
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interpreted as a UNIX-style date, but interpreted as local time rather
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than UTC.
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.It Dv lestring16
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2006-06-19 07:52:15 +00:00
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A two-byte unicode (UCS16) string in little-endian byte order.
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.It Dv melong
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A four-byte value in middle-endian (PDP-11) byte order.
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.It Dv medate
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A four-byte value in middle-endian (PDP-11) byte order,
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interpreted as a UNIX date.
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.It Dv meldate
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2009-01-02 02:57:16 +00:00
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A four-byte value in middle-endian (PDP-11) byte order,
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interpreted as a UNIX-style date, but interpreted as local time rather
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than UTC.
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.It Dv indirect
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Starting at the given offset, consult the magic database again.
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.It Dv regex
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A regular expression match in extended POSIX regular expression syntax
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(like egrep).
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Regular expressions can take exponential time to process, and their
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performance is hard to predict, so their use is discouraged.
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When used in production environments, their performance
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should be carefully checked.
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The type specification can be optionally followed by
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.Dv /[c][s] .
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The
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.Dq c
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flag makes the match case insensitive, while the
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.Dq s
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flag update the offset to the start offset of the match, rather than the end.
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The regular expression is tested against line
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.Dv N + 1
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onwards, where
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.Dv N
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is the given offset.
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Line endings are assumed to be in the machine's native format.
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.Dv ^
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and
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.Dv $
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match the beginning and end of individual lines, respectively,
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not beginning and end of file.
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.It Dv search
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A literal string search starting at the given offset.
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The same modifier flags can be used as for string patterns.
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The modifier flags (if any) must be followed by
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.Dv /number
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the range, that is, the number of positions at which the match will be
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attempted, starting from the start offset.
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This is suitable for
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searching larger binary expressions with variable offsets, using
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.Dv \e
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escapes for special characters.
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The offset works as for regex.
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.It Dv default
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This is intended to be used with the test
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.Em x
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(which is always true) and a message that is to be used if there are
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no other matches.
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.El
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.Pp
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Each top-level magic pattern (see below for an explanation of levels)
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is classified as text or binary according to the types used.
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Types
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.Dq regex
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and
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.Dq search
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are classified as text tests, unless non-printable characters are used
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in the pattern.
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All other tests are classified as binary.
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A top-level
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pattern is considered to be a test text when all its patterns are text
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patterns; otherwise, it is considered to be a binary pattern.
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When
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matching a file, binary patterns are tried first; if no match is
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found, and the file looks like text, then its encoding is determined
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and the text patterns are tried.
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.Pp
|
1994-09-03 19:16:28 +00:00
|
|
|
The numeric types may optionally be followed by
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Am]
|
1994-09-03 19:16:28 +00:00
|
|
|
and a numeric value,
|
|
|
|
to specify that the value is to be AND'ed with the
|
2003-02-28 05:19:36 +00:00
|
|
|
numeric value before any comparisons are done.
|
|
|
|
Prepending a
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv u
|
1994-09-03 19:16:28 +00:00
|
|
|
to the type indicates that ordered comparisons should be unsigned.
|
2008-01-13 20:35:16 +00:00
|
|
|
.It Dv test
|
2003-02-28 05:19:36 +00:00
|
|
|
The value to be compared with the value from the file.
|
2004-08-09 08:45:41 +00:00
|
|
|
If the type is
|
|
|
|
numeric, this value
|
1994-09-03 19:16:28 +00:00
|
|
|
is specified in C form; if it is a string, it is specified as a C string
|
|
|
|
with the usual escapes permitted (e.g. \en for new-line).
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
1994-09-03 19:16:28 +00:00
|
|
|
Numeric values
|
|
|
|
may be preceded by a character indicating the operation to be performed.
|
|
|
|
It may be
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv = ,
|
1994-09-03 19:16:28 +00:00
|
|
|
to specify that the value from the file must equal the specified value,
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Lt] ,
|
1994-09-03 19:16:28 +00:00
|
|
|
to specify that the value from the file must be less than the specified
|
|
|
|
value,
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Gt] ,
|
1994-09-03 19:16:28 +00:00
|
|
|
to specify that the value from the file must be greater than the specified
|
|
|
|
value,
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Am] ,
|
2006-06-19 07:52:15 +00:00
|
|
|
to specify that the value from the file must have set all of the bits
|
1994-09-03 19:16:28 +00:00
|
|
|
that are set in the specified value,
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv ^ ,
|
2006-06-19 07:52:15 +00:00
|
|
|
to specify that the value from the file must have clear any of the bits
|
1996-01-23 12:29:07 +00:00
|
|
|
that are set in the specified value, or
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv ~ ,
|
2006-06-19 07:52:15 +00:00
|
|
|
the value specified after is negated before tested.
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv x ,
|
2003-02-28 05:19:36 +00:00
|
|
|
to specify that any value will match.
|
|
|
|
If the character is omitted, it is assumed to be
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv = .
|
|
|
|
Operators
|
|
|
|
.Dv \*[Am] ,
|
|
|
|
.Dv ^ ,
|
|
|
|
and
|
|
|
|
.Dv ~
|
|
|
|
don't work with floats and doubles.
|
2009-01-02 02:57:16 +00:00
|
|
|
The operator
|
|
|
|
.Dv !\&
|
2006-06-19 07:52:15 +00:00
|
|
|
specifies that the line matches if the test does
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em not
|
2006-06-19 07:52:15 +00:00
|
|
|
succeed.
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
1994-09-03 19:16:28 +00:00
|
|
|
Numeric values are specified in C form; e.g.
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv 13
|
1994-09-03 19:16:28 +00:00
|
|
|
is decimal,
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv 013
|
1994-09-03 19:16:28 +00:00
|
|
|
is octal, and
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv 0x13
|
1994-09-03 19:16:28 +00:00
|
|
|
is hexadecimal.
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
2009-01-02 02:57:16 +00:00
|
|
|
For string values, the string from the
|
|
|
|
file must match the specified string.
|
1994-09-03 19:16:28 +00:00
|
|
|
The operators
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv = ,
|
|
|
|
.Dv \*[Lt]
|
1994-09-03 19:16:28 +00:00
|
|
|
and
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Gt]
|
1994-09-03 19:16:28 +00:00
|
|
|
(but not
|
2008-01-13 20:35:16 +00:00
|
|
|
.Dv \*[Am] )
|
1994-09-03 19:16:28 +00:00
|
|
|
can be applied to strings.
|
|
|
|
The length used for matching is that of the string argument
|
2003-02-28 05:19:36 +00:00
|
|
|
in the magic file.
|
2009-01-02 02:57:16 +00:00
|
|
|
This means that a line can match any non-empty string (usually used to
|
|
|
|
then print the string), with
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em \*[Gt]\e0
|
2009-01-02 02:57:16 +00:00
|
|
|
(because all non-empty strings are greater than the empty string).
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
|
|
|
The special test
|
|
|
|
.Em x
|
|
|
|
always evaluates to true.
|
2011-10-06 06:01:12 +00:00
|
|
|
.It Dv message
|
2008-01-13 20:35:16 +00:00
|
|
|
The message to be printed if the comparison succeeds.
|
|
|
|
If the string contains a
|
|
|
|
.Xr printf 3
|
1994-09-03 19:16:28 +00:00
|
|
|
format specification, the value from the file (with any specified masking
|
|
|
|
performed) is printed using the message as the format string.
|
2009-01-02 02:57:16 +00:00
|
|
|
If the string begins with
|
|
|
|
.Dq \eb ,
|
|
|
|
the message printed is the remainder of the string with no whitespace
|
|
|
|
added before it: multiple matches are normally separated by a single
|
|
|
|
space.
|
2008-01-13 20:35:16 +00:00
|
|
|
.El
|
|
|
|
.Pp
|
2009-05-02 06:25:51 +00:00
|
|
|
An APPLE 4+4 character APPLE creator and type can be specified as:
|
2011-10-06 06:01:12 +00:00
|
|
|
.Bd -literal -offset indent
|
2009-05-02 06:25:51 +00:00
|
|
|
!:apple CREATYPE
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2009-01-02 02:57:16 +00:00
|
|
|
A MIME type is given on a separate line, which must be the next
|
|
|
|
non-blank or comment line after the magic line that identifies the
|
|
|
|
file type, and has the following format:
|
2011-10-06 06:01:12 +00:00
|
|
|
.Bd -literal -offset indent
|
2009-01-02 02:57:16 +00:00
|
|
|
!:mime MIMETYPE
|
|
|
|
.Ed
|
|
|
|
.Pp
|
|
|
|
i.e. the literal string
|
|
|
|
.Dq !:mime
|
|
|
|
followed by the MIME type.
|
|
|
|
.Pp
|
|
|
|
An optional strength can be supplied on a separate line which refers to
|
|
|
|
the current magic description using the following format:
|
2011-10-06 06:01:12 +00:00
|
|
|
.Bd -literal -offset indent
|
2009-01-02 02:57:16 +00:00
|
|
|
!:strength OP VALUE
|
|
|
|
.Ed
|
|
|
|
.Pp
|
|
|
|
The operand
|
|
|
|
.Dv OP
|
2011-10-06 06:01:12 +00:00
|
|
|
can be:
|
2009-01-02 02:57:16 +00:00
|
|
|
.Dv + ,
|
|
|
|
.Dv - ,
|
|
|
|
.Dv * ,
|
|
|
|
or
|
|
|
|
.Dv /
|
|
|
|
and
|
|
|
|
.Dv VALUE
|
|
|
|
is a constant between 0 and 255.
|
|
|
|
This constant is applied using the specified operand
|
|
|
|
to the currently computed default magic strength.
|
|
|
|
.Pp
|
1994-09-03 19:16:28 +00:00
|
|
|
Some file formats contain additional information which is to be printed
|
2006-06-19 07:52:15 +00:00
|
|
|
along with the file type or need additional tests to determine the true
|
|
|
|
file type.
|
|
|
|
These additional tests are introduced by one or more
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em \*[Gt]
|
2006-06-19 07:52:15 +00:00
|
|
|
characters preceding the offset.
|
2003-02-28 05:19:36 +00:00
|
|
|
The number of
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em \*[Gt]
|
1994-09-03 19:16:28 +00:00
|
|
|
on the line indicates the level of the test; a line with no
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em \*[Gt]
|
1994-09-03 19:16:28 +00:00
|
|
|
at the beginning is considered to be at level 0.
|
2006-06-19 07:52:15 +00:00
|
|
|
Tests are arranged in a tree-like hierarchy:
|
2011-10-06 06:01:12 +00:00
|
|
|
if the test on a line at level
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em n
|
2006-06-19 07:52:15 +00:00
|
|
|
succeeds, all following tests at level
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em n+1
|
2011-10-06 06:01:12 +00:00
|
|
|
are performed, and the messages printed if the tests succeed, until a line
|
2006-06-19 07:52:15 +00:00
|
|
|
with level
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em n
|
2006-06-19 07:52:15 +00:00
|
|
|
(or less) appears.
|
|
|
|
For more complex files, one can use empty messages to get just the
|
|
|
|
"if/then" effect, in the following way:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable
|
|
|
|
\*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows)
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
Offsets do not need to be constant, but can also be read from the file
|
|
|
|
being examined.
|
1994-09-03 19:16:28 +00:00
|
|
|
If the first character following the last
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em \*[Gt]
|
1994-09-03 19:16:28 +00:00
|
|
|
is a
|
2011-10-06 06:01:12 +00:00
|
|
|
.Em \&(
|
1994-09-03 19:16:28 +00:00
|
|
|
then the string after the parenthesis is interpreted as an indirect offset.
|
1996-01-23 12:29:07 +00:00
|
|
|
That means that the number after the parenthesis is used as an offset in
|
2003-02-28 05:19:36 +00:00
|
|
|
the file.
|
|
|
|
The value at that offset is read, and is used again as an offset
|
|
|
|
in the file.
|
|
|
|
Indirect offsets are of the form:
|
2009-05-02 06:25:51 +00:00
|
|
|
.Em (( x [.[bislBISL]][+\-][ y ]) .
|
2006-06-19 07:52:15 +00:00
|
|
|
The value of
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em x
|
|
|
|
is used as an offset in the file.
|
2009-05-02 06:25:51 +00:00
|
|
|
A byte, id3 length, short or long is read at that offset depending on the
|
|
|
|
.Em [bislBISLm]
|
2003-02-28 05:19:36 +00:00
|
|
|
type specifier.
|
|
|
|
The capitalized types interpret the number as a big endian
|
2003-02-15 18:53:17 +00:00
|
|
|
value, whereas the small letter versions interpret the number as a little
|
2006-06-19 07:52:15 +00:00
|
|
|
endian value;
|
|
|
|
the
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em m
|
2006-06-19 07:52:15 +00:00
|
|
|
type interprets the number as a middle endian (PDP-11) value.
|
2003-02-28 05:19:36 +00:00
|
|
|
To that number the value of
|
2008-01-13 20:35:16 +00:00
|
|
|
.Em y
|
2003-02-28 05:19:36 +00:00
|
|
|
is added and the result is used as an offset in the file.
|
|
|
|
The default type if one is not specified is long.
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
That way variable length structures can be examined:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
# MS Windows executables are also valid MS-DOS executables
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS)
|
|
|
|
# skip the whole block below if it is not an extended executable
|
|
|
|
\*[Gt]0x18 leshort \*[Gt]0x3f
|
|
|
|
\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
|
|
|
|
\*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2)
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2009-01-02 02:57:16 +00:00
|
|
|
This strategy of examining has a drawback: You must make sure that
|
2006-06-19 07:52:15 +00:00
|
|
|
you eventually print something, or users may get empty output (like, when
|
|
|
|
there is neither PE\e0\e0 nor LE\e0\e0 in the above example)
|
2008-01-13 20:35:16 +00:00
|
|
|
.Pp
|
2009-01-02 02:57:16 +00:00
|
|
|
If this indirect offset cannot be used directly, simple calculations are
|
2006-06-19 07:52:15 +00:00
|
|
|
possible: appending
|
2009-01-02 02:57:16 +00:00
|
|
|
.Em [+-*/%\*[Am]|^]number
|
2006-06-19 07:52:15 +00:00
|
|
|
inside parentheses allows one to modify
|
|
|
|
the value read from the file before it is used as an offset:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
# MS Windows executables are also valid MS-DOS executables
|
|
|
|
0 string MZ
|
|
|
|
# sometimes, the value at 0x18 is less that 0x40 but there's still an
|
|
|
|
# extended executable, simply appended to the file
|
|
|
|
\*[Gt]0x18 leshort \*[Lt]0x40
|
|
|
|
\*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
|
|
|
|
\*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
Sometimes you do not know the exact offset as this depends on the length or
|
2008-01-13 20:35:16 +00:00
|
|
|
position (when indirection was used before) of preceding fields.
|
|
|
|
You can specify an offset relative to the end of the last up-level
|
|
|
|
field using
|
|
|
|
.Sq \*[Am]
|
2006-06-19 07:52:15 +00:00
|
|
|
as a prefix to the offset:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Gt]0x3f
|
|
|
|
\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
|
|
|
|
# immediately following the PE signature is the CPU type
|
|
|
|
\*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386
|
|
|
|
\*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
Indirect and relative offsets can be combined:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Lt]0x40
|
|
|
|
\*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
|
|
|
|
# if it's not COFF, go back 512 bytes and add the offset taken
|
|
|
|
# from byte 2/3, which is yet another way of finding the start
|
|
|
|
# of the extended executable
|
|
|
|
\*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver)
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
Or the other way around:
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Gt]0x3f
|
|
|
|
\*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
|
|
|
|
# at offset 0x80 (-4, since relative offsets start at the end
|
|
|
|
# of the up-level match) inside the LE header, we find the absolute
|
|
|
|
# offset to the code area, where we look for a specific signature
|
|
|
|
\*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed
|
|
|
|
.Ed
|
|
|
|
.Pp
|
2006-06-19 07:52:15 +00:00
|
|
|
Or even both!
|
2008-01-13 20:35:16 +00:00
|
|
|
.Bd -literal -offset indent
|
|
|
|
0 string MZ
|
|
|
|
\*[Gt]0x18 leshort \*[Gt]0x3f
|
|
|
|
\*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
|
|
|
|
# at offset 0x58 inside the LE header, we find the relative offset
|
|
|
|
# to a data area where we look for a specific signature
|
|
|
|
\*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive
|
|
|
|
.Ed
|
|
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.Pp
|
2006-06-19 07:52:15 +00:00
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Finally, if you have to deal with offset/length pairs in your file, even the
|
2008-01-13 20:35:16 +00:00
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second value in a parenthesized expression can be taken from the file itself,
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using another set of parentheses.
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Note that this additional indirect offset is always relative to the
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start of the main indirect offset.
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.Bd -literal -offset indent
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0 string MZ
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\*[Gt]0x18 leshort \*[Gt]0x3f
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\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
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# search for the PE section called ".idata"...
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\*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata
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# ...and go to the end of it, calculated from start+length;
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# these are located 14 and 10 bytes after the section name
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\*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive
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.Ed
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|
.Sh SEE ALSO
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.Xr file __CSECTION__
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\- the command that reads this file.
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|
.Sh BUGS
|
2006-06-19 07:52:15 +00:00
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The formats
|
2008-01-13 20:35:16 +00:00
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|
.Dv long ,
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.Dv belong ,
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.Dv lelong ,
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.Dv melong ,
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.Dv short ,
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.Dv beshort ,
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.Dv leshort ,
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.Dv date ,
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.Dv bedate ,
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.Dv medate ,
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.Dv ledate ,
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.Dv beldate ,
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.Dv leldate ,
|
1994-09-03 19:16:28 +00:00
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and
|
2008-01-13 20:35:16 +00:00
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|
.Dv meldate
|
1996-01-23 12:29:07 +00:00
|
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|
are system-dependent; perhaps they should be specified as a number
|
2006-06-19 07:52:15 +00:00
|
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of bytes (2B, 4B, etc),
|
1994-09-03 19:16:28 +00:00
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|
since the files being recognized typically come from
|
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|
a system on which the lengths are invariant.
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|
.\"
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|
.\" From: guy@sun.uucp (Guy Harris)
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|
.\" Newsgroups: net.bugs.usg
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|
.\" Subject: /etc/magic's format isn't well documented
|
2004-08-09 08:45:41 +00:00
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|
.\" Message-ID: <2752@sun.uucp>
|
1994-09-03 19:16:28 +00:00
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|
.\" Date: 3 Sep 85 08:19:07 GMT
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.\" Organization: Sun Microsystems, Inc.
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.\" Lines: 136
|
2006-06-19 07:52:15 +00:00
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.\"
|
1994-09-03 19:16:28 +00:00
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|
.\" Here's a manual page for the format accepted by the "file" made by adding
|
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|
.\" the changes I posted to the S5R2 version.
|
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|
.\"
|
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|
|
.\" Modified for Ian Darwin's version of the file command.
|