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MAGIC(4)                                                              MAGIC(4)



NAME
       magic(4,5) - file(1,n) command's magic(4,5) number file(1,n)

DESCRIPTION
       This  manual page documents the format of the magic(4,5) file(1,n) as used by the
       file(1,n)(1) command, version(1,3,5) 4.10.  The file(1,n) command identifies the type of
       a  file(1,n)  using,  among  other tests, a test for whether the file(1,n) begins
       with a certain magic(4,5) number.  The file(1,n) /usr/share/misc/file(1,n)/magic(4,5) spec-
       ifies what magic(4,5) numbers are to be tested for, what message to print if(3,n)
       a particular magic(4,5) number  is  found,  and  additional  information  to
       extract from the file.

       Each  line  of  the file(1,n) specifies a test to be performed.  A test com-
       pares the data starting at a particular  offset  in(1,8)  the  file(1,n)  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(1,8) bytes, into the file(1,n) 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(1,8) this  machine's
                         native byte order.

                long     A four-byte value (on most systems) in(1,8) this machine's
                         native byte order.

                string(3,n)   A string(3,n) of bytes.  The string(3,n) type specification can
                         be  optionally  followed  by /[Bbc]*.  The ``B'' flag
                         compacts whitespace in(1,8) the target, which must contain
                         at  least one whitespace character.  If the magic(4,5) has
                         n consecutive blanks, the target  needs  at  least  n
                         consecutive  blanks  to match.  The ``b'' flag treats
                         every blank in(1,8)  the  target  as  an  optional  blank.
                         Finally  the  ``c''  flag, specifies case insensitive
                         matching: lowercase characters  in(1,8)  the  magic(4,5)  match
                         both  lower  and upper case characters in(1,8) the targer,
                         whereas upper case characters in(1,8) the magic(4,5), only much
                         uppercase characters in(1,8) the target.

                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(1,2,n) rather than UTC.

                beshort  A two-byte value (on most systems) in(1,8) big-endian byte
                         order.

                belong   A  four-byte  value  (on  most systems) in(1,8) big-endian
                         byte order.

                bedate   A four-byte value (on  most  systems)  in(1,8)  big-endian
                         byte order, interpreted as a Unix date.

                leshort  A  two-byte  value (on most systems) in(1,8) little-endian
                         byte order.

                lelong   A four-byte value (on most systems) in(1,8)  little-endian
                         byte order.

                ledate   A  four-byte value (on most systems) in(1,8) little-endian
                         byte order, interpreted as a UNIX date.

                leldate  A four-byte value (on most systems) in(1,8)  little-endian
                         byte  order,  interpreted  as  a UNIX-style date, but
                         interpreted as local time(1,2,n) rather than UTC.

       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(1,8) C form; if(3,n) it  is  a
              string(3,n),  it  is  specified  as a C string(3,n) 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(1,n) must equal the specified value, <, to  spec-
              ify that the value from the file(1,n) must be less(1,3) than the specified
              value, >, to specify that  the  value  from  the  file(1,n)  must  be
              greater  than  the specified value, &, to specify that the value
              from the file(1,n) must have set(7,n,1 builtins) all of the bits that are set(7,n,1 builtins) in(1,8)  the
              specified value, ^, to specify that the value from the file(1,n) must
              have clear(1,3x,3x clrtobot) any of the bits that are set(7,n,1 builtins) in(1,8) the specified  value,
              or x, to specify that any value will match.  If the character is
              omitted, it is assumed to be =.

              Numeric values are specified in(1,8) C form; e.g.  13 is decimal, 013
              is octal, and 0x13 is hexadecimal.

              For  string(3,n) values, the byte string(3,n) from the file(1,n) 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(3,n) argument in(1,8) the magic(4,5) file.  This means that  a  line
              can  match any string(3,n), and then presumably print that string(3,n), by
              doing >\0  (because  all  strings  are  greater  than  the  null
              string(3,n)).

       message
              The  message  to  be printed if(3,n) the comparison succeeds.  If the
              string(3,n) contains a printf(1,3,1 builtins)(3) format specification, the value from
              the file(1,n) (with any specified masking performed) is printed using
              the message as the format string.

       Some file(1,n) formats contain additional information which is to be printed
       along  with  the  file(1,n)  type.  A line which begins with the character >
       indicates additional tests and messages to be printed.  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.  Each line at  level  n+1  is
       under  the  control of the line at level n most closely preceding it in(1,8)
       the magic(4,5) file.  If the test on a line at level n succeeds,  the  tests
       specified  in(1,8)  all the subsequent lines at level n+1 are performed, and
       the messages printed if(3,n) the tests succeed.  The next line  at  level  n
       terminates  this.   If  the first character following the last > is a (
       then the string(3,n) after the parenthesis is  interpreted  as  an  indirect
       offset.  That means that the number after the parenthesis is used as an
       offset in(1,8) the file.  The value at that offset  is  read(2,n,1 builtins),  and  is  used
       again  as  an  offset  in(1,8)  the file.  Indirect offsets are of the form:
       ((x[.[bslBSL]][+-][y]).  The value of x is used as  an  offset  in(1,8)  the
       file.  A  byte,  short  or long is read(2,n,1 builtins) at that offset depending on the
       [bslBSL] 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.  To that number  the  value  of  y  is
       added  and  the  result  is used as an offset in(1,8) the file.  The default
       type if(3,n) one is not specified is long.

       Sometimes you do not know the exact  offset  as  this  depends  on  the
       length  of preceding fields.  You can specify an offset relative to the
       end of the last uplevel field (of course this may only be done for sub-
       level  tests, i.e.  test beginning with > ).  Such a relative offset is
       specified using & as a prefix to the offset.

BUGS
       The formats  long,  belong,  lelong,  short,  beshort,  leshort,  date,
       bedate,  and ledate are system-dependent; perhaps they should be speci-
       fied as a number of bytes (2B, 4B, etc), since the files  being  recog-
       nized  typically come from a system on which the lengths are invariant.

       There is (currently) no support for specified-endian data to be used in(1,8)
       indirect offsets.

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



                                 Public Domain                        MAGIC(4)

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