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 4.17.  The file 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/file/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 com-
       pares 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 suc-
       ceeds, 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.

                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 inter-
                         preted as the an unsigned length. The string  is  not
                         NUL terminated.

                date     A four-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.

                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.

                bedate   A four-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.

                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.

                ledate   A four-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.

                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 speci-
                         fication  can  be optionally followed by /c for case-
                         insensitive  matches.   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 begin-
                         ning 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 charac-
                         ters.

       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 =.  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).

       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.

       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 calcula-
       tions  possible: appending [+-*/%&|^]<number> inside parentheses allows
       one to modify the value read from the file before it is used as an off-
       set:

           # 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
       uplevel 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 uplevel 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 parenthesed expression can be taken from the
       file itself, using another set of parentheses.  Note  that  this  addi-
       tional  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

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.

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

                                 Public Domain                        MAGIC(5)