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MAGIC(5)										 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 3.39. 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/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 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.

		string	 A  string of bytes. The string type specification can be optionally fol-
			 lowed 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: low-
			 ercase  characters  in the magic match both lower and upper case charac-
			 ters 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.

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

		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.

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

		leldate  A four-byte value (on most systems) in little-endian byte order,  inter-
			 preted  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  per-
	      formed.  It may be =, to specify that the value from the file must equal the speci-
	      fied value, , to specify that the value from the file must be less than the  speci-
	      fied  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 con-
       trol 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 termi-
       nates this.  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	offset	 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 [bslBSL] type specifier. The capitalized
       types interpret the number as a big endian value, whereas the small letter versions inter-
       pet  the  number  as a little endian 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.

       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 sublevel 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 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.

       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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