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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, version "5.03".  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 con‐
			  tain 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 insen‐
			  sitive matching: lowercase characters in the magic
			  match both lower and upper case characters 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 inter‐
			  preted 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, inter‐
			  preted as a Unix date.

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

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

	      beqldate	  An eight-byte value in big-endian byte order, inter‐
			  preted 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 inter‐
			  preted 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 per‐
			  formance is hard to predict, so their use is dis‐
			  couraged. When used in production environments,
			  their performance should be carefully checked. The
			  type specification can be optionally followed by
			  /[c][s].  The “c” flag makes the match case insensi‐
			  tive, 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 off‐
			  set. 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 pat‐
	      terns; 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 deter‐
	      mined 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 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 =.  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 spec‐
	      ified 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 mes‐
	      sage 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 sepa‐
	      rated 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 constant 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 > char‐
     acters 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 per‐
     formed, 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 off‐
     set 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 offset 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 parentheses.	Note that this additional
     indirect offset is always relative to the start of the main indirect off‐
     set.

	   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-depen‐
     dent; 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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