NAME | DESCRIPTION | SEE ALSO | BUGS | COLOPHON

MAGIC(4)                BSD Kernel Interfaces Manual                MAGIC(4)

NAME         top

     magic — file command's magic pattern file

DESCRIPTION         top

     This manual page documents the format of magic files as used by the
     file(1) command, version 5.30.  The file(1) command identifies the type
     of a file using, among other tests, a test for whether the file con‐
     tains certain “magic patterns”.  The database of these “magic patterns”
     is usually located in a binary file in /usr/local/share/misc/magic.mgc
     or a directory of source text magic pattern fragment files in
     /usr/local/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 fol‐
     lowing 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 num‐
                          ber in this machine's native byte order.

              double      A 64-bit double precision IEEE floating point num‐
                          ber in this machine's native byte order.

              string      A string of bytes.  The string type specification
                          can be optionally followed by /[WwcCtbT]*.  The
                          “W” 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
                          “w” flag treats every blank in the magic as an
                          optional blank.  The “c” flag specifies 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.  The “C” flag specifies case insensitive
                          matching: upper case characters in the magic match
                          both lower and upper case characters in the tar‐
                          get, whereas lower 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”.  The “t” flag forces the test to
                          be done for text files, while the “b” flag forces
                          the test to be done for binary files.  The “T”
                          flag causes the string to be trimmed, i.e. leading
                          and trailing whitespace 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 4 byte big endian length.
                          h  A 2 byte big endian length.
                          L  A 4 byte little endian length.
                          l  A 2 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       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.

              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 num‐
                          ber in big-endian byte order.

              bedouble    A 64-bit double precision IEEE floating point num‐
                          ber 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,
                          interpreted 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,
                          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 num‐
                          ber in little-endian byte order.

              ledouble    A 64-bit double precision IEEE floating point num‐
                          ber 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 regu‐
                          lar 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 envi‐
                          ronments, 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 spec‐
                          ified, an implicit byte count also computed assum‐
                          ing 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, respec‐
                          tively, 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 search expression must con‐
                          tain 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 expres‐
                          sions 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.

              For compatibility with the Single UNIX Standard, the type
              specifiers dC and d1 are equivalent to byte, the type speci‐
              fiers 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 pat‐
              tern.  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 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 inter‐
              nal representation.

              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 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
     [[.,][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 depend‐
     ing on the [bislBISLm] 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.

     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         top

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

BUGS         top

     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 Specifi‐
     cation 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.

COLOPHON         top

     This page is part of the file (a file type guesser) project.  Informa‐
     tion about the project can be found at http://www.darwinsys.com/file/.
     If you have a bug report for this manual page, see
     http://bugs.gw.com/my_view_page.php.  This page was obtained from the
     project's upstream Git read-only mirror of the CVS repository
     https://github.com/glensc/file on 2017-05-03.  If you discover any ren‐
     dering problems in this HTML version of the page, or you believe there
     is a better or more up-to-date source for the page, or you have correc‐
     tions or improvements to the information in this COLOPHON (which is not
     part of the original manual page), send a mail to man-pages@man7.org

BSD                           February 12, 2017                          BSD