Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
MAGIC(5)		  FreeBSD File Formats Manual		      MAGIC(5)

NAME
     magic -- file command's magic pattern file

DESCRIPTION
     This manual page documents	the format of the magic	file as	used by	the
     file(1) command, version "5.11".  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 file /usr/share/misc/magic 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.

     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 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.

     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
			  order.

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

	      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	/[WwcCtb]*.  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 characters in the target.  To do	a complete
			  case insensitive 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.

	      pstring	  A Pascal-style string	where the first	byte/short/int
			  is interpreted as the	an 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 2 byte big endian length.
			  h  A 2 byte big little length.
			  L  A 4 byte big endian length.
			  l  A 4 byte big little 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.

	      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
			  local	time rather than UTC.

	      beqldate	  An eight-byte	value in big-endian byte order,	inter-
			  preted 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.

	      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,
			  interpreted as a UNIX	date.

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

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

	      leqldate	  An eight-byte	value 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 in middle-endian (PDP-11) byte
			  order.

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

	      meldate	  A four-byte value in middle-endian (PDP-11) byte
			  order, 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.

	      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
			  type specification can be optionally followed	by
			  /[c][s].  The	``c'' flag makes the match case	insen-
			  sitive, while	the ``s'' flag update the offset to
			  the start offset of the match, rather	than the end.
			  The regular expression is tested against line	N + 1
			  onwards, where N is the given	offset.	 Line endings
			  are assumed to be in the machine's native format.  ^
			  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	modifier flags (if any)	must
			  be followed by /number the range, that is, the num-
			  ber of positions at which the	match will be
			  attempted, starting from the start offset.  This is
			  suitable for searching larger	binary expressions
			  with variable	offsets, using \ escapes for special
			  characters.  The offset works	as for regex.

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

	      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
	      patterns;	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 determined 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
	      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.  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.

	      For string values, the string from the file must match the spec-
	      ified 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	non-empty string (usually used to then print the
	      string), with _\0	(because all non-empty strings are greater
	      than the empty string).

	      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
	      separated	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
     [.[bislBISL]][+-][	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 [bislBISLm]	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 a 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 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
     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			April 20, 2011			  FreeBSD 10.1

NAME | DESCRIPTION | SEE ALSO | BUGS

Want to link to this manual page? Use this URL:
<http://www.freebsd.org/cgi/man.cgi?query=magic&sektion=5&manpath=FreeBSD+9.3-RELEASE>

home | help