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MAGIC(5)                  FreeBSD File Formats Manual                 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 "4.23".  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 file /usr/share/misc/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.

                  quad            An eight-byte value (on most systems) in
                                  this machine's native byte order.

                  float           A 32-bit (on most systems) single precision
                                  IEEE floating point number in this machine's
                                  native byte order.

                  double          A 64-bit (on most systems) 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 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 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.

                  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.

                  bequad          An eight-byte value (on most systems) in
                                  big-endian byte order.

                  befloat         A 32-bit (on most systems) single precision
                                  IEEE floating point number in big-endian
                                  byte order.

                  bedouble        A 64-bit (on most systems) double precision
                                  IEEE floating point number in big-endian
                                  byte order.

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

                  beqdate         An eight-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.

                  beqldate        An eight-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.

                  lequad          An eight-byte value (on most systems) in
                                  little-endian byte order.

                  lefloat         A 32-bit (on most systems) single precision
                                  IEEE floating point number in little-endian
                                  byte order.

                  ledouble        A 64-bit (on most systems) double precision
                                  IEEE floating point number in little-endian
                                  byte order.

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

                  leqdate         An eight-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.

                  leqldate        An eight-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 specification can be optionally
                                  followed by /[cse]*.  The ``c'' flag makes
                                  the match case insensitive, while the ``s''
                                  or ``e'' flags update the offset to the
                                  starting or ending offsets of the match
                                  (only one should be used).  By default,
                                  regex does not update the offset.  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 beginning 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 characters.

                  default         This is intended to be used with the text x
                                  (which is always true) and a message that is
                                  to be used if there are no other matches.

     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
                  specify 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.
                  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).

                  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.

     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
     calculations 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
     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.

FreeBSD 11.0-PRERELEASE        January 10, 2007        FreeBSD 11.0-PRERELEASE

NAME | DESCRIPTION | SEE ALSO | BUGS

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