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MAGIC(5)			     BSD 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, ver-
     sion 5.04.  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 /[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 char-
			  acters in the target, whereas upper case characters in the magic only
			  match uppercase characters in the target.

	      pstring	  A Pascal-style string where the first byte is interpreted as the an
			  unsigned length.  The string is not NUL terminated.

	      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, interpreted as a Unix date.

	      beqdate	  An eight-byte value in big-endian byte order, interpreted as a Unix
			  date.

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

	      beqldate	  An eight-byte value 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.

	      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 interpreted 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 performance is hard to predict, so their use is discouraged.
			  When used in production environments, their performance should be care-
			  fully checked. The type specification can be optionally followed by
			  /[c][s].  The ``c'' flag makes the match case insensitive, 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 offset. 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 number 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 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 ~, 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 specified 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 con-
     stant 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 > 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, 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 offset
     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 off-
     set 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 parenthe-
     ses.  Note that this additional 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

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-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.

BSD					 August 30, 2008				      BSD
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