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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 "4.10".  The file 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  specifies
       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 com-
       pares 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 suc-
       ceeds, 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.

		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.

		date	 A four-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.

		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.


		ledate	 A  four-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.

       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 x, to specify that any value will match.  If the character is
	      omitted, it is assumed to be =.

	      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).

       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.

       Some file formats contain additional information which is to be printed
       along  with  the  file  type.  A line which begins with the character >
       indicates additional tests and messages to be printed.  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.  Each line at	level  n+1  is
       under  the  control of the line at level n most closely preceding it in
       the magic file.	If the test on a line at level n succeeds,  the  tests
       specified  in  all the subsequent lines at level n+1 are performed, and
       the messages printed if the tests succeed.  The next line  at  level  n
       terminates  this.   If  the first character following the last > is a (
       then the string after the parenthesis is  interpreted  as  an  indirect
       added  and  the	result	is used as an offset in the file.  The default
       type if one is not specified is long.

       Sometimes you do not know the exact  offset  as	this  depends  on  the
       length  of preceding fields.  You can specify an offset relative to the
       end of the last uplevel field (of course this may only be done for sub-
       level  tests, i.e.  test beginning with > ).  Such a relative offset is
       specified using & as a prefix to the offset.

BUGS

       The formats  long,  belong,  lelong,  short,  beshort,  leshort,  date,
       bedate,	and ledate are system-dependent; perhaps they should be speci-
       fied as a number of bytes (2B, 4B, etc), since the files  being	recog-
       nized  typically come from a system on which the lengths are invariant.

       There is (currently) no support for specified-endian data to be used in
       indirect offsets.

SEE ALSO

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

				 Public Domain			      MAGIC(5)

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