Provided by: libmagic1t64_5.45-3build1_amd64 bug

NAME

     magic — file command's magic pattern file

DESCRIPTION

     This manual page documents the format of magic files as used by the file(1) command, version
     5.45.  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 database of these “magic
     patterns” is usually located in a binary file in /usr/share/misc/magic.mgc or a directory of
     source text magic pattern fragment files in /usr/share/misc/magic.  The database 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.

     The format of the source fragment files that are used to build this database is as follows:
     Each line of a fragment 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.  This offset can be a negative number if it is:
                 The first direct offset of the magic entry (at continuation level 0), in which
                  case it is interpreted an offset from end end of the file going backwards.
                  This works only when a file descriptor to the file is available and it is a
                  regular file.
                 A continuation offset relative to the end of the last up-level field (&).

     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 a /<width> option and optionally followed by a set of flags
                          /[bCcftTtWw]*.  The width limits the number of characters to be copied.
                          Zero means all characters.  The following flags are supported:
                              b  Force binary file test.
                              C  Use upper case insensitive matching: upper case characters in
                                 the magic match both lower and upper case characters in the
                                 target, whereas lower case characters in the magic only match
                                 upper case characters in the target.
                              c  Use lower case insensitive matching: lower case characters in
                                 the magic match both lower and upper case characters in the
                                 target, whereas upper case characters in the magic only match
                                 upper case characters in the target.  To do a complete case
                                 insensitive match, specify both “c” and “C”.
                              f  Require that the matched string is a full word, not a partial
                                 word match.
                              T  Trim the string, i.e. leading and trailing whitespace
                              t  Force text file test.
                              W  Compact 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.
                              w  Treat every blank in the magic as an optional blank.  is deleted
                                 before the string is printed.

              pstring     A Pascal-style string where the first byte/short/int is interpreted as
                          the unsigned length.  The length defaults to byte and can be specified
                          as a modifier.  The following modifiers are supported:
                              B  A byte length (default).
                              H  A 2 byte big endian length.
                              h  A 2 byte little endian length.
                              L  A 4 byte big endian length.
                              l  A 4 byte little endian length.
                              J  The length includes itself in its count.
                          The string is not NUL terminated.  “J” is used rather than the more
                          valuable “I” because this type of length is a feature of the JPEG
                          format.

              date        A four-byte value interpreted as a UNIX date.

              qdate       An 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.

              qwdate      An eight-byte value interpreted as a Windows-style date.

              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.

              beqwdate    An eight-byte value in big-endian byte order, interpreted as a Windows-
                          style date.

              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.

              leqwdate    An eight-byte value in little-endian byte order, interpreted as a
                          Windows-style date.

              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.  The
                          offset of the indirect magic is by default absolute in the file, but
                          one can specify /r to indicate that the offset is relative from the
                          beginning of the entry.

              name        Define a “named” magic instance that can be called from another use
                          magic entry, like a subroutine call.  Named instance direct magic
                          offsets are relative to the offset of the previous matched entry, but
                          indirect offsets are relative to the beginning of the file as usual.
                          Named magic entries always match.

              use         Recursively call the named magic starting from the current offset.  If
                          the name of the referenced begins with a ^ then the endianness of the
                          magic is switched; if the magic mentioned leshort for example, it is
                          treated as beshort and vice versa.  This is useful to avoid duplicating
                          the rules for different endianness.

              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 carefully checked.  The size of the string to search should
                          also be limited by specifying /<length>, to avoid performance issues
                          scanning long files.  The type specification can also be optionally
                          followed by /[c][s][l].  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 “l” modifier, changes the limit of length to
                          mean number of lines instead of a byte count.  Lines are delimited by
                          the platforms native line delimiter.  When a line count is specified,
                          an implicit byte count also computed assuming each line is 80
                          characters long.  If neither a byte or line count is specified, the
                          search is limited automatically to 8KiB.  ^ 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 search
                          expression must contain the range in the form /number, 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 order of modifier and number is not relevant.

              default     This is intended to be used with the test x (which is always true) and
                          it has no type.  It matches when no other test at that continuation
                          level has matched before.  Clearing that matched tests for a
                          continuation level, can be done using the clear test.

              clear       This test is always true and clears the match flag for that
                          continuation level.  It is intended to be used with the default test.

              der         Parse the file as a DER Certificate file.  The test field is used as a
                          der type that needs to be matched.  The DER types are: eoc, bool, int,
                          bit_str, octet_str, null, obj_id, obj_desc, ext, real, enum, embed,
                          utf8_str, rel_oid, time, res2, seq, set, num_str, prt_str, t61_str,
                          vid_str, ia5_str, utc_time, gen_time, gr_str, vis_str, gen_str,
                          univ_str, char_str, bmp_str, date, tod, datetime, duration, oid-iri,
                          rel-oid-iri.  These types can be followed by an optional numeric size,
                          which indicates the field width in bytes.

              guid        A Globally Unique Identifier, parsed and printed as XXXXXXXX-XXXX-XXXX-
                          XXXX-XXXXXXXXXXXX.  It's format is a string.

              offset      This is a quad value indicating the current offset of the file.  It can
                          be used to determine the size of the file or the magic buffer.  For
                          example the magic entries:

                                -0      offset  x       this file is %lld bytes
                                -0      offset  <=100   must be more than 100 \
                                    bytes and is only %lld

              octal       A string representing an octal number.

     For compatibility with the Single UNIX Standard, the type specifiers dC and d1 are
     equivalent to byte, the type specifiers uC and u1 are equivalent to ubyte, the type
     specifiers dS and d2 are equivalent to short, the type specifiers uS and u2 are equivalent
     to ushort, the type specifiers dI, dL, and d4 are equivalent to long, the type specifiers
     uI, uL, and u4 are equivalent to ulong, the type specifier d8 is equivalent to quad, the
     type specifier u8 is equivalent to uquad, and the type specifier s is equivalent to string.
     In addition, the type specifier dQ is equivalent to quad and the type specifier uQ is
     equivalent to uquad.

     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.
     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.  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.

     Numeric operations are not performed on date types, instead the numeric value is interpreted
     as an offset.

     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).

     Dates are treated as numerical values in the respective internal representation.

     The special test x always evaluates to true.
     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 slash-separated list of commonly found filename extensions can be specified as:

         !:ext   ext[/ext...]

   i.e. the literal string “!:ext” followed by a slash-separated list of commonly found
   extensions; for example for JPEG images:

         !:ext jpeg/jpg/jpe/jfif

   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 > 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 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 [[.,][bBcCeEfFgGhHiIlmsSqQ]][+-][ 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 [bBcCeEfFgGhHiIlmsSqQ] type specifier.  The value is treated as
   signed if “”, is specified or unsigned if “”.  is specified.  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.  The following types are recognized:

         Type    Sy Mnemonic   Sy Endian Sy Size
         bcBc    Byte/Char     N/A       1
         efg     Double        Little    8
         EFG     Double        Big       8
         hs      Half/Short    Little    2
         HS      Half/Short    Big       2
         i       ID3           Little    4
         I       ID3           Big       4
         m       Middle        Middle    4
         o       Octal         Textual   Variable
         q       Quad          Little    8
         Q       Quad          Big       8

   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 (such as 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

   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

   If you have a list of known values at a particular continuation level, and you want to provide
   a switch-like default case:

         # clear that continuation level match
         >18     clear
         >18     lelong  1       one
         >18     lelong  2       two
         >18     default x
         # print default match
         >>18    lelong  x       unmatched 0x%x

SEE ALSO

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

BUGS

     The formats long, belong, lelong, melong, short, beshort, and leshort do not depend on the
     length of the C data types short and long on the platform, even though the Single UNIX
     Specification implies that they do.  However, as OS X Mountain Lion has passed the Single
     UNIX Specification validation suite, and supplies a version of file(1) in which they do not
     depend on the sizes of the C data types and that is built for a 64-bit environment in which
     long is 8 bytes rather than 4 bytes, presumably the validation suite does not test whether,
     for example long refers to an item with the same size as the C data type long.  There should
     probably be type names int8, uint8, int16, uint16, int32, uint32, int64, and uint64, and
     specified-byte-order variants of them, to make it clearer that those types have specified
     widths.