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MAGIC(5)		    BSD	File Formats Manual		      MAGIC(5)

NAME
     magic -- file command's magic pattern file

DESCRIPTION
     This manual page documents	the format of magic files as used by the
     file(1) command, version "5.32".  The file(1) command identifies the type
     of	a file using, among other tests, a test	for whether the	file contains
     certain "magic patterns".	The database of	these "magic patterns" is usu-
     ally located in a binary file in /usr/share/misc/magic.mgc	or a directory
     of	source text magic pattern fragment files in /usr/share/misc/magic.
     The database specifies what patterns are to be tested for,	what message
     or	MIME type to print if a	particular pattern is found, and additional
     information to extract from the file.

     The format	of the source fragment files that are used to build this data-
     base is as	follows: Each line of a	fragment file specifies	a test to be
     performed.	 A test	compares the data starting at a	particular offset in
     the file with a byte value, a string or a numeric value.  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.  This	offset can be a	negative num-
	      ber if it	is:
	      +o	  The first direct offset of the magic entry (at continuation
		  level	0), in which case it is	interpreted an offset from end
		  end of the file going	backwards.  This works only when a
		  file descriptor to the file is a available and it is a regu-
		  lar file.
	      +o	  A continuation offset	relative to the	end of the last	up-
		  level	field (&).

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

	      byte	  A one-byte value.

	      short	  A two-byte value in this machine's native byte or-
			  der.

	      long	  A four-byte value in this machine's native byte or-
			  der.

	      quad	  An eight-byte	value in this machine's	native byte
			  order.

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

	      double	  A 64-bit 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	/[WwcCtbT]*.  The "W"
			  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 "w"	flag
			  treats every blank in	the magic as an	optional
			  blank.  The "c" flag specifies case insensitive
			  matching: lower case characters in the magic match
			  both lower and upper case characters in the target,
			  whereas upper	case characters	in the magic only
			  match	upper case characters in the target.  The "C"
			  flag specifies case insensitive matching: upper case
			  characters in	the magic match	both lower and upper
			  case characters in the target, whereas lower case
			  characters in	the magic only match upper case	char-
			  acters in the	target.	 To do a complete case insen-
			  sitive match,	specify	both "c" and "C".  The "t"
			  flag forces the test to be done for text files,
			  while	the "b"	flag forces the	test to	be done	for
			  binary files.	 The "T" flag causes the string	to be
			  trimmed, i.e.	leading	and trailing whitespace	is
			  deleted before the string is printed.

	      pstring	  A Pascal-style string	where the first	byte/short/int
			  is interpreted as the	unsigned length.  The length
			  defaults to byte and can be specified	as a modifier.
			  The following	modifiers are supported:
			  B  A byte length (default).
			  H  A 4 byte big endian length.
			  h  A 2 byte big endian length.
			  L  A 4 byte little endian length.
			  l  A 2 byte little endian length.
			  J  The length	includes itself	in its count.
			  The string is	not NUL	terminated.  "J" is used
			  rather than the more valuable	"I" because this type
			  of length is a feature of the	JPEG format.

	      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.

	      qwdate	  An eight-byte	value interpreted as a Windows-style
			  date.

	      beid3	  A 32-bit ID3 length in big-endian byte order.

	      beshort	  A two-byte value in big-endian byte order.

	      belong	  A four-byte value in big-endian byte order.

	      bequad	  An eight-byte	value in big-endian byte order.

	      befloat	  A 32-bit single precision IEEE floating point	number
			  in big-endian	byte order.

	      bedouble	  A 64-bit double precision IEEE floating point	number
			  in big-endian	byte order.

	      bedate	  A four-byte value in big-endian byte order, inter-
			  preted as a Unix date.

	      beqdate	  An eight-byte	value in big-endian byte order,	inter-
			  preted as a Unix date.

	      beldate	  A four-byte value in big-endian byte order, inter-
			  preted as a UNIX-style date, but interpreted as lo-
			  cal time rather than UTC.

	      beqldate	  An eight-byte	value in big-endian byte order,	inter-
			  preted as a UNIX-style date, but interpreted as lo-
			  cal time rather than UTC.

	      beqwdate	  An eight-byte	value in big-endian byte order,	inter-
			  preted as a Windows-style date.

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

	      leid3	  A 32-bit ID3 length in little-endian byte order.

	      leshort	  A two-byte value in little-endian byte order.

	      lelong	  A four-byte value in little-endian byte order.

	      lequad	  An eight-byte	value in little-endian byte order.

	      lefloat	  A 32-bit single precision IEEE floating point	number
			  in little-endian byte	order.

	      ledouble	  A 64-bit double precision IEEE floating point	number
			  in little-endian byte	order.

	      ledate	  A four-byte value in little-endian byte order, in-
			  terpreted as a UNIX date.

	      leqdate	  An eight-byte	value in little-endian byte order, in-
			  terpreted as a UNIX date.

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

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

	      leqwdate	  An eight-byte	value in little-endian byte order, in-
			  terpreted as a Windows-style date.

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

	      melong	  A four-byte value in middle-endian (PDP-11) byte or-
			  der.

	      medate	  A four-byte value in middle-endian (PDP-11) byte or-
			  der, interpreted as a	UNIX date.

	      meldate	  A four-byte value in middle-endian (PDP-11) byte or-
			  der, interpreted as a	UNIX-style date, but inter-
			  preted as local time rather than UTC.

	      indirect	  Starting at the given	offset,	consult	the magic
			  database again.  The offset of the indirect magic is
			  by default absolute in the file, but one can specify
			  /r to	indicate that the offset is relative from the
			  beginning of the entry.

	      name	  Define a "named" magic instance that can be called
			  from another use magic entry,	like a subroutine
			  call.	 Named instance	direct magic offsets are rela-
			  tive to the offset of	the previous matched entry,
			  but indirect offsets are relative to the beginning
			  of the file as usual.	 Named magic entries always
			  match.

	      use	  Recursively call the named magic starting from the
			  current offset.  If the name of the referenced be-
			  gins with a ^	then the endianness of the magic is
			  switched; if the magic mentioned leshort for exam-
			  ple, it is treated as	beshort	and vice versa.	 This
			  is useful to avoid duplicating the rules for differ-
			  ent endianness.

	      regex	  A regular expression match in	extended POSIX regular
			  expression syntax (like egrep).  Regular expressions
			  can take exponential time to process,	and their per-
			  formance is hard to predict, so their	use is dis-
			  couraged.  When used in production environments,
			  their	performance should be carefully	checked.  The
			  size of the string to	search should also be limited
			  by specifying	/<length>, to avoid performance	issues
			  scanning long	files.	The type specification can
			  also be optionally followed by /[c][s][l].  The "c"
			  flag makes the match case insensitive, while the "s"
			  flag update the offset to the	start offset of	the
			  match, rather	than the end.  The "l" modifier,
			  changes the limit of length to mean number of	lines
			  instead of a byte count.  Lines are delimited	by the
			  platforms native line	delimiter.  When a line	count
			  is specified,	an implicit byte count also computed
			  assuming each	line is	80 characters long.  If	nei-
			  ther a byte or line count is specified, the search
			  is limited automatically to 8KiB.  ^ and $ match the
			  beginning and	end of individual lines, respectively,
			  not beginning	and end	of file.

	      search	  A literal string search starting at the given	off-
			  set.	The same modifier flags	can be used as for
			  string patterns.  The	search expression must contain
			  the range in the form	/number, that is the number of
			  positions at which the match will be attempted,
			  starting from	the start offset.  This	is suitable
			  for searching	larger binary expressions with vari-
			  able offsets,	using \	escapes	for special charac-
			  ters.	 The order of modifier and number is not rele-
			  vant.

	      default	  This is intended to be used with the test x (which
			  is always true) and it has no	type.  It matches when
			  no other test	at that	continuation level has matched
			  before.  Clearing that matched tests for a continua-
			  tion level, can be done using	the clear test.

	      clear	  This test is always true and clears the match	flag
			  for that continuation	level.	It is intended to be
			  used with the	default	test.

	      For compatibility	with the Single	UNIX Standard, the type	speci-
	      fiers dC and d1 are equivalent to	byte, the type specifiers uC
	      and u1 are equivalent to ubyte, the type specifiers dS and d2
	      are equivalent to	short, the type	specifiers uS and u2 are
	      equivalent to ushort, the	type specifiers	dI, dL,	and d4 are
	      equivalent to long, the type specifiers uI, uL, and u4 are
	      equivalent to ulong, the type specifier d8 is equivalent to
	      quad, the	type specifier u8 is equivalent	to uquad, and the type
	      specifier	s is equivalent	to string.  In addition, the type
	      specifier	dQ is equivalent to quad and the type specifier	uQ is
	      equivalent to uquad.

	      Each top-level magic pattern (see	below for an explanation of
	      levels) is classified as text or binary according	to the types
	      used.  Types "regex" and "search"	are classified as text tests,
	      unless non-printable characters are used in the pattern.	All
	      other tests are classified as binary.  A top-level pattern is
	      considered to be a test text when	all its	patterns are text pat-
	      terns; otherwise,	it is considered to be a binary	pattern.  When
	      matching a file, binary patterns are tried first;	if no match is
	      found, and the file looks	like text, then	its encoding is	deter-
	      mined and	the text patterns are tried.

	      The numeric types	may optionally be followed by &	and a numeric
	      value, to	specify	that the value is to be	AND'ed with the	nu-
	      meric 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 op-
	      eration to be performed.	It may be =, to	specify	that the value
	      from the file must equal the specified value, <, to specify 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 spec-
	      ify that any value will match.  If the character is omitted, it
	      is assumed to be =.  Operators &,	^, and ~ don't work with
	      floats and doubles.  The operator	! 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.

	      Numeric operations are not performed on date types, instead the
	      numeric value is interpreted as an offset.

	      For string values, the string from the file must match the spec-
	      ified string.  The operators =, <	and > (but not &) can be ap-
	      plied 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	non-empty string (usually used to then print the
	      string), with _\0	(because all non-empty strings are greater
	      than the empty string).

	      Dates are	treated	as numerical values in the respective internal
	      representation.

	      The special test x always	evaluates to true.

     message  The message 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.

     An	APPLE 4+4 character APPLE creator and type can be specified as:

	   !:apple CREATYPE

     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:

	   !:mime  MIMETYPE

     i.e. the literal string "!:mime" followed by the MIME type.

     An	optional strength can be supplied on a separate	line which refers to
     the current magic description using the following format:

	   !:strength OP VALUE

     The operand OP can	be: +, -, *, or	/ and VALUE is a constant between 0
     and 255.  This constant is	applied	using the specified operand to the
     currently computed	default	magic strength.

     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 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, until 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
     [[.,][bBcCeEfFgGhHiIlmsSqQ]][+-][ y ]).  The value	of x is	used as	an
     offset in the file.  A byte, id3 length, short or long is read at that
     offset depending on the [bBcCeEfFgGhHiIlmsSqQ] type specifier.  The value
     is	treated	as signed if "", is specified or unsigned if "".  is speci-
     fied.  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.
     The following types are recognized:

	   Type	   Sy Mnemonic	 Sy Endian Sy Size
	   bcBc	   Byte/Char	 N/A	   1
	   efg	   Double	 Little	   8
	   EFG	   Double	 Big	   8
	   hs	   Half/Short	 Little	   2
	   HS	   Half/Short	 Big	   2
	   i	   ID3		 Little	   4
	   I	   ID3		 Big	   4
	   m	   Middle	 Middle	   4
	   q	   Quad		 Little	   8
	   Q	   Quad		 Big	   8

     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 a drawback:	you must make sure that	you
     eventually	print something, or users may get empty	output (such as	when
     there is neither PE\0\0 nor LE\0\0	in the above example).

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

	   # 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 us-
     ing `&' 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

     If	you have to deal with offset/length pairs in your file,	even the sec-
     ond value in a parenthesized expression can be taken from the file	it-
     self, using another set of	parentheses.  Note that	this additional	indi-
     rect offset is always relative to the start of the	main indirect offset.

	   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

     If	you have a list	of known values	at a particular	continuation level,
     and you want to provide a switch-like default case:

	   # clear that	continuation level match
	   >18	   clear
	   >18	   lelong  1	   one
	   >18	   lelong  2	   two
	   >18	   default x
	   # print default match
	   >>18	   lelong  x	   unmatched 0x%x

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

BUGS
     The formats long, belong, lelong, melong, short, beshort, and leshort do
     not depend	on the length of the C data types short	and long on the	plat-
     form, even	though the Single UNIX Specification implies that they do.
     However, as OS X Mountain Lion has	passed the Single UNIX Specification
     validation	suite, and supplies a version of file(1) in which they do not
     depend on the sizes of the	C data types and that is built for a 64-bit
     environment in which long is 8 bytes rather than 4	bytes, presumably the
     validation	suite does not test whether, for example long refers to	an
     item with the same	size as	the C data type	long.  There should probably
     be	type names int8, uint8,	int16, uint16, int32, uint32, int64, and
     uint64, and specified-byte-order variants of them,	to make	it clearer
     that those	types have specified widths.

BSD				 June 22, 2018				   BSD

NAME | DESCRIPTION | SEE ALSO | BUGS

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