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MAGIC(5)		  FreeBSD File Formats Manual		      MAGIC(5)

NAME
     magic -- file command's magic number file

DESCRIPTION
     This manual page documents	the format of the magic	file as	used by	the
     file(1) command, version "4.23".  The file(1) command identifies the type
     of	a file using, among other tests, a test	for whether the	file begins
     with a certain ``magic number''.  The file	/usr/share/misc/magic speci-
     fies what magic numbers are to be tested for, what	message	to print if a
     particular	magic number is	found, and additional information to extract
     from the file.

     Each line of the file specifies a test to be performed.  A	test compares
     the data starting at a particular offset in the file with a 1-byte,
     2-byte, or	4-byte numeric value or	a string.  If the test succeeds, a
     message is	printed.  The line consists of the following fields:

     offset   A	number specifying the offset, in bytes,	into the file of the
	      data which is to be tested.

     type     The type of the data to be tested.  The possible values are:

	      byte	  A one-byte value.

	      short	  A two-byte value (on most systems) in	this machine's
			  native byte order.

	      long	  A four-byte value (on	most systems) in this
			  machine's native byte	order.

	      quad	  An eight-byte	value (on most systems)	in this
			  machine's native byte	order.

	      float	  A 32-bit (on most systems) single precision IEEE
			  floating point number	in this	machine's native byte
			  order.

	      double	  A 64-bit (on most systems) double precision IEEE
			  floating point number	in this	machine's native byte
			  order.

	      string	  A string of bytes.  The string type specification
			  can be optionally followed by	/[Bbc]*.  The ``B''
			  flag compacts	whitespace in the target, which	must
			  contain at least one whitespace character.  If the
			  magic	has n consecutive blanks, the target needs at
			  least	n consecutive blanks to	match.	The ``b'' flag
			  treats every blank in	the target as an optional
			  blank.  Finally the ``c'' flag, specifies case
			  insensitive matching:	lowercase characters in	the
			  magic	match both lower and upper case	characters in
			  the targer, whereas upper case characters in the
			  magic, only much uppercase characters	in the target.

	      pstring	  A pascal style string	where the first	byte is	inter-
			  preted as the	an unsigned length.  The string	is not
			  NUL terminated.

	      date	  A four-byte value interpreted	as a UNIX date.

	      qdate	  A eight-byte value interpreted as a UNIX date.

	      ldate	  A four-byte value interpreted	as a UNIX-style	date,
			  but interpreted as local time	rather than UTC.

	      qldate	  An eight-byte	value interpreted as a UNIX-style
			  date,	but interpreted	as local time rather than UTC.

	      beshort	  A two-byte value (on most systems) in	big-endian
			  byte order.

	      belong	  A four-byte value (on	most systems) in big-endian
			  byte order.

	      bequad	  An eight-byte	value (on most systems)	in big-endian
			  byte order.

	      befloat	  A 32-bit (on most systems) single precision IEEE
			  floating point number	in big-endian byte order.

	      bedouble	  A 64-bit (on most systems) double precision IEEE
			  floating point number	in big-endian byte order.

	      bedate	  A four-byte value (on	most systems) in big-endian
			  byte order, interpreted as a Unix date.

	      beqdate	  An eight-byte	value (on most systems)	in big-endian
			  byte order, interpreted as a Unix date.

	      beldate	  A four-byte value (on	most systems) in big-endian
			  byte order, interpreted as a UNIX-style date,	but
			  interpreted as local time rather than	UTC.

	      beqldate	  An eight-byte	value (on most systems)	in big-endian
			  byte order, interpreted as a UNIX-style date,	but
			  interpreted as local time rather than	UTC.

	      bestring16  A two-byte unicode (UCS16) string in big-endian byte
			  order.

	      leshort	  A two-byte value (on most systems) in	little-endian
			  byte order.

	      lelong	  A four-byte value (on	most systems) in little-endian
			  byte order.

	      lequad	  An eight-byte	value (on most systems)	in little-
			  endian byte order.

	      lefloat	  A 32-bit (on most systems) single precision IEEE
			  floating point number	in little-endian byte order.

	      ledouble	  A 64-bit (on most systems) double precision IEEE
			  floating point number	in little-endian byte order.

	      ledate	  A four-byte value (on	most systems) in little-endian
			  byte order, interpreted as a UNIX date.

	      leqdate	  An eight-byte	value (on most systems)	in little-
			  endian byte order, interpreted as a UNIX date.

	      leldate	  A four-byte value (on	most systems) in little-endian
			  byte order, interpreted as a UNIX-style date,	but
			  interpreted as local time rather than	UTC.

	      leqldate	  An eight-byte	value (on most systems)	in little-
			  endian byte order, interpreted as a UNIX-style date,
			  but interpreted as local time	rather than UTC.

	      lestring16  A two-byte unicode (UCS16) string in little-endian
			  byte order.

	      melong	  A four-byte value (on	most systems) in middle-endian
			  (PDP-11) byte	order.

	      medate	  A four-byte value (on	most systems) in middle-endian
			  (PDP-11) byte	order, interpreted as a	UNIX date.

	      meldate	  A four-byte value (on	most systems) in middle-endian
			  (PDP-11) byte	order, interpreted as a	UNIX-style
			  date,	but interpreted	as local time rather than UTC.

	      regex	  A regular expression match in	extended POSIX regular
			  expression syntax (much like egrep).	The type spec-
			  ification can	be optionally followed by /[cse]*.
			  The ``c'' flag makes the match case insensitive,
			  while	the ``s'' or ``e'' flags update	the offset to
			  the starting or ending offsets of the	match (only
			  one should be	used).	By default, regex does not
			  update the offset.  The regular expression is	always
			  tested against the first N lines, where N is the
			  given	offset,	thus it	is only	useful for (single-
			  byte encoded)	text.  ^ and $ will match the begin-
			  ning and end of individual lines, respectively, not
			  beginning and	end of file.

	      search	  A literal string search starting at the given	off-
			  set.	It must	be followed by <number>	which speci-
			  fies how many	matches	shall be attempted (the
			  range).  This	is suitable for	searching larger
			  binary expressions with variable offsets, using \
			  escapes for special characters.

	      default	  This is intended to be used with the text x (which
			  is always true) and a	message	that is	to be used if
			  there	are no other matches.

     The numeric types may optionally be followed by & and a numeric value, to
     specify that the value is to be AND'ed with the numeric value before any
     comparisons are done.  Prepending a u to the type indicates that ordered
     comparisons should	be unsigned.

     test     The value	to be compared with the	value from the file.  If the
	      type is numeric, this value is specified in C form; if it	is a
	      string, it is specified as a C string with the usual escapes
	      permitted	(e.g. \n for new-line).

	      Numeric values may be preceded by	a character indicating the
	      operation	to be performed.  It may be =, to specify that the
	      value from the file must equal the specified value, <, to	spec-
	      ify that the value from the file must be less than the specified
	      value, >,	to specify that	the value from the file	must be
	      greater than the specified value,	&, to specify that the value
	      from the file must have set all of the bits that are set in the
	      specified	value, ^, to specify that the value from the file must
	      have clear any of	the bits that are set in the specified value,
	      or ~, the	value specified	after is negated before	tested.	 x, to
	      specify that any value will match.  If the character is omitted,
	      it is assumed to be =.  Operators	&, ^, and ~ don't work with
	      floats and doubles.  For all tests except	string and regex,
	      operation	!  specifies that the line matches if the test does
	      not succeed.

	      Numeric values are specified in C	form; e.g.  13 is decimal, 013
	      is octal,	and 0x13 is hexadecimal.

	      For string values, the byte string from the file must match the
	      specified	byte string.  The operators =, < and > (but not	&) can
	      be applied to strings.  The length used for matching is that of
	      the string argument in the magic file.  This means that a	line
	      can match	any string, and	then presumably	print that string, by
	      doing _\0	(because all strings are greater than the null
	      string).

	      The special test x always	evaluates to true.  message The	mes-
	      sage to be printed if the	comparison succeeds.  If the string
	      contains a printf(3) format specification, the value from	the
	      file (with any specified masking performed) is printed using the
	      message as the format string.  If	the string begins with ``\b'',
	      the message printed is the remainder of the string with no
	      whitespace added before it: multiple matches are normally	sepa-
	      rated by a single	space.

     Some file formats contain additional information which is to be printed
     along with	the file type or need additional tests to determine the	true
     file type.	 These additional tests	are introduced by one or more _	char-
     acters preceding the offset.  The number of _ on the line indicates the
     level of the test;	a line with no _ at the	beginning is considered	to be
     at	level 0.  Tests	are arranged in	a tree-like hierarchy: If a the	test
     on	a line at level	n succeeds, all	following tests	at level n+1 are per-
     formed, and the messages printed if the tests succeed, untile a line with
     level n (or less) appears.	 For more complex files, one can use empty
     messages to get just the "if/then"	effect,	in the following way:

	   0	  string   MZ
	   >0x18  leshort  <0x40   MS-DOS executable
	   >0x18  leshort  >0x3f   extended PC executable (e.g., MS Windows)

     Offsets do	not need to be constant, but can also be read from the file
     being examined.  If the first character following the last	_ is a ( then
     the string	after the parenthesis is interpreted as	an indirect offset.
     That means	that the number	after the parenthesis is used as an offset in
     the file.	The value at that offset is read, and is used again as an off-
     set in the	file.  Indirect	offsets	are of the form: (( x [.[bslBSL]][+-][
     y ]).  The	value of x is used as an offset	in the file.  A	byte, short or
     long is read at that offset depending on the [bslBSLm] type specifier.
     The capitalized types interpret the number	as a big endian	value, whereas
     the small letter versions interpret the number as a little	endian value;
     the m type	interprets the number as a middle endian (PDP-11) value.  To
     that number the value of y	is added and the result	is used	as an offset
     in	the file.  The default type if one is not specified is long.

     That way variable length structures can be	examined:

	   # MS	Windows	executables are	also valid MS-DOS executables
	   0	       string  MZ
	   >0x18       leshort <0x40   MZ executable (MS-DOS)
	   # skip the whole block below	if it is not an	extended executable
	   >0x18       leshort >0x3f
	   >>(0x3c.l)  string  PE\0\0  PE executable (MS-Windows)
	   >>(0x3c.l)  string  LX\0\0  LX executable (OS/2)

     This strategy of examining	has one	drawback: You must make	sure that you
     eventually	print something, or users may get empty	output (like, when
     there is neither PE\0\0 nor LE\0\0	in the above example)

     If	this indirect offset cannot be used as-is, there are simple calcula-
     tions possible: appending [+-*/%_|^]_number_ inside parentheses allows
     one to modify the value read from the file	before it is used as an	off-
     set:

	   # 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
	   >0x18       leshort <0x40
	   >>(4.s*512) leshort 0x014c  COFF executable (MS-DOS,	DJGPP)
	   >>(4.s*512) leshort !0x014c MZ executable (MS-DOS)

     Sometimes you do not know the exact offset	as this	depends	on the length
     or	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 `&' as a prefix to the offset:

	   0	       string  MZ
	   >0x18       leshort >0x3f
	   >>(0x3c.l)  string  PE\0\0	 PE executable (MS-Windows)
	   # immediately following the PE signature is the CPU type
	   >>>&0       leshort 0x14c	 for Intel 80386
	   >>>&0       leshort 0x184	 for DEC Alpha

     Indirect and relative offsets can be combined:

	   0		 string	 MZ
	   >0x18	 leshort <0x40
	   >>(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
	   >>>&(2.s-514) string	 LE	 LE executable (MS Windows VxD driver)

     Or	the other way around:

	   0		     string  MZ
	   >0x18	     leshort >0x3f
	   >>(0x3c.l)	     string  LE\0\0  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
	   >>>(&0x7c.l+0x26) string  UPX     \b, UPX compressed

     Or	even both!

	   0		    string  MZ
	   >0x18	    leshort >0x3f
	   >>(0x3c.l)	    string  LE\0\0 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
	   >>>&(&0x54.l-3)  string  UNACE  \b, ACE self-extracting archive

     Finally, if you have to deal with offset/length pairs in your file, even
     the second	value in a parenthesized expression can	be taken from the file
     itself, using another set of parentheses.	Note that this additional
     indirect offset is	always relative	to the start of	the main indirect off-
     set.

	   0		     string	  MZ
	   >0x18	     leshort	  >0x3f
	   >>(0x3c.l)	     string	  PE\0\0 PE executable (MS-Windows)
	   # search for	the PE section called ".idata"...
	   >>>&0xf4	     search/0x140 .idata
	   # ...and go to the end of it, calculated from start+length;
	   # these are located 14 and 10 bytes after the section name
	   >>>>(&0xe.l+(-4)) string	  PK\3\4 \b, ZIP self-extracting archive

SEE ALSO
     file(1) - the command that	reads this file.

BUGS
     The formats long, belong, lelong, melong, short, beshort, leshort,	date,
     bedate, medate, ledate, beldate, leldate, and meldate are system-depen-
     dent; perhaps they	should be specified as a number	of bytes (2B, 4B,
     etc), since the files being recognized typically come from	a system on
     which the lengths are invariant.

FreeBSD	10.1		       January 10, 2007			  FreeBSD 10.1

NAME | DESCRIPTION | SEE ALSO | BUGS

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