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OpenSolaris 2009.06 - man page for magic (opensolaris section 4)

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magic(4)				   File Formats 				 magic(4)

       magic - file command's magic number file


       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 /etc/magic file, or a file speci-
       fied  as  an option-argument to the -m or -M options of file(1), specifies what magic num-
       bers 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 position-sensitive test to perform. A test compares the
       data starting at a particular offset in the file with a 1-byte, 2-byte, 4-byte, or  8-byte
       numeric	value or string. If the test succeeds, a message is printed. The line consists of
       the following fields (separated by tabs): offset type value message

       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, d1, dC		  A one-byte signed value.

		  short, d2, dS 	  A 2-byte signed value.

		  long, d4, dI, dL, d	  A 4-byte signed value.

		  llong, d8		  An 8-byte signed value

		  ubyte, u1, uC 	  A one-byte unsigned value.

		  ushort, u2, uS	  A 2-byte unsigned value.

		  ulong, u4, uI, uL, u	  A 4-byte unsigned value.

		  ullong, u8		  An 8-byte unsigned value.

		  string, s		  A string of bytes.

		  All  type specifiers, except for string and s, may be followed by a mask speci-
		  fier of the form &number. If a mask specifier is given,  the	value  is  AND'ed
		  with	the  number before any comparisons are done. The number is specified in C
		  form. For instance, 13 is decimal, 013 is octal, and 0x13 is hexadecimal.

       value	  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 (for instance, \n for NEWLINE).

		  Numeric values may be preceded by a character indicating the	operation  to  be
		  performed, as follows:

		  =    The value from the file must equal the specified value.

		  <    The value from the file must be less than the specified value.

		  >    The value from the file must be greater than the specified value.

		  &    All  the  bits  in  the	specified value must be set in the value from the

		  ^    At least one of the bits in the specified value must not  be  set  in  the
		       value from the file.

		  x    Any value will match.

		  If the character is omitted, it is assumed to be "=".

		  For  comparison  of  numeric values, the sign and size of both the value in the
		  file and the value from the value field of the magic entry will match  that  of
		  the  corresponding  type  field.  If	there  is a non-zero mask (&) in the type
		  field, the comparison will be unsigned.

		  For string values, the byte string from the file must match the specified  byte
		  string.  The	byte  string from the file which is matched is the same length as
		  the specified byte string. If the value is a string, it can contain the follow-
		  ing sequences:

		  \character	 The backslash-escape sequences \\, \a, \b, \f, \n, \r, \t, \v.

		  \octal	 Octal	sequences  that  can be used to represent characters with
				 specific coded values. An octal sequence consists of a backslash
				 followed  by  the  longest sequence of one, two, or three octal-
				 digit characters(01234567).

       message	  The message to be printed if the comparison succeeds. If the string contains	a
		  printf(3C)  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 mes-
       sages to be printed. If the test on the line preceding the first line with a ">" succeeds,
       the  tests specified in all the subsequent lines beginning with ">" are performed, and the
       messages are printed if the tests succeed. The next line which does not begin with  a  ">"
       terminates this.


       file(1), file(1B), printf(3C)

       In  Solaris 9 and prior releases, the file utility may have performed unsigned comparisons
       for types byte, short, and long. Old user-defined magic files, which were  specified  with
       the  -m	option,  will  need modification of byte, short, and long entries to their corre-
       sponding unsigned types (ubyte, ushort, or ulong) for those entries for which all  of  the
       following are true:

	   o	  The entry uses the "<" or the ">" operator.

	   o	  The type field does not contain a non-zero mask.

	   o	  The intention of the entry is to test unsigned values.

       For example, if the following entry is expected to match any non-zero, one-byte value from
       the file, including values for which the sign bit is on:

	 #offset type	 value	 message
	 0	 byte	 >0	 this matches any non-zero value

       then that entry should be changed to:

	 0	 ubyte	  >0	 this matches any non-zero value

       In Solaris 7 through Solaris 9, when applying tests for	magic  file  entries  whose  type
       field is the numeric type "short" or "long", the file utility in the x86 environment would
       switch the byte order of the numeric values read. Starting in Solaris 10, the  byte  order
       will  not  be switched on x86. A test for a numeric value whose byte order is identical in
       both little- and big-endian architectures may require two magic file  entries,  to  ensure
       that  the  test correctly identifies files in both environments. For example, a magic file
       entry that will match on a big-endian system may look like this:

	 0	 long	   0xf00000ff	   extended accounting file

       Its corresponding magic file entry that will match the same value on a little-endian  sys-
       tem would look like this:

	 0	 long	   0xff0000f0	   extended accounting file

       There should be more than one level of subtests, with the level indicated by the number of
       `>' at the beginning of the line.

SunOS 5.11				    6 Feb 2004					 magic(4)
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