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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 4.17.  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/file/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.

		pstring	 A  pascal style string where the first byte is inter‐
			 preted as the an unsigned length. The string  is  not
			 NUL terminated.

		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, interpreted as a Unix date.

		beldate	 A  four-byte  value  (on  most systems) in big-endian
			 byte order, interpreted 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.

		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, 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.

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

		melong	 A four-byte value (on most systems) in	 middle-endian
			 (PDP-11) byte order.

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

		meldate	 A four-byte value (on most systems) in	 middle-endian
			 (PDP-11)  byte	 order,	 interpreted  as  a UNIX-style
			 date, but interpreted as local time rather than UTC.

		regex	 A regular expression match in extended POSIX  regular
			 expression syntax (much like egrep).  The type speci‐
			 fication can be optionally followed by /c  for	 case-
			 insensitive   matches.	  The  regular	expression  is
			 always tested against the first N lines, where	 N  is
			 the given offset, thus it is only useful for (single-
			 byte encoded) text.  ^ and $ will match the beginning
			 and end of individual lines, respectively, not begin‐
			 ning and end of file.

		search	 A literal string search starting at the given offset.
			 It  must be followed by /<number> which specifies how
			 many matches shall be attempted (the range).  This is
			 suitable for searching larger binary expressions with
			 variable offsets, using \ escapes for special charac‐
			 ters.

       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 =.  For all tests except string  and	regex,
	      operation	 !   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 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 or need additional tests to determine the true
       file type.  These additional tests are introduced  by  one  or  more  >
       characters 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 a
       the test on a line at level n succeeds, all following  tests  at	 level
       n+1  are	 performed,  and  the  messages	 printed if the tests succeed,
       untile 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  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
       [bslBSLm] 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 one 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 as-is, there are simple calcula‐
       tions possible: appending [+-*/%&|^]<number> inside parentheses	allows
       one to modify the value read from the file before it is used as an off‐
       set:

	   # 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
       uplevel 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 uplevel 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 parenthesed expression can be taken from the
       file  itself,  using  another  set of parentheses. Note that this addi‐
       tional indirect 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

BUGS
       The  formats  long,  belong,  lelong,  melong, short, beshort, leshort,
       date, bedate, medate, ledate, beldate, leldate, and meldate 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.

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

				 Public Domain			      MAGIC(5)
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