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magic(5)                         File Formats                         magic(5)

       magic - file command's magic number file


       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  /etc/magic  file, or a file specified as an option-argument to the
       -m or -M options of file(1), 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 position-sensitive test to perform. A
       test compares the data starting at a particular offset in the file with
       a 1-byte, 2-byte, 4-byte, or 8-byte numeric value  or  string.  If  the
       test succeeds, a message is printed. The line consists of the following
       fields (separated by tabs): offset  type  value  message

       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, d1, dC            A one-byte signed value.

                  short, d2, dS           A 2-byte signed value.

                  long, d4, dI, dL, d     A 4-byte signed value.

                  llong, d8               An 8-byte signed value

                  ubyte, u1, uC           A one-byte unsigned value.

                  ushort, u2, uS          A 2-byte unsigned value.

                  ulong, u4, uI, uL, u    A 4-byte unsigned value.

                  ullong, u8              An 8-byte unsigned value.

                  string, s               A string of bytes.

                  All  type  specifiers,  except for string and s, may be fol‐
                  lowed by a mask specifier of the form  &number.  If  a  mask
                  specifier  is  given,  the  value  is AND'ed with the number
                  before any comparisons are done. The number is specified  in
                  C  form. For instance, 13 is decimal, 013 is octal, and 0x13
                  is hexadecimal.

       value      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 (for instance, \n for NEWLINE).

                  Numeric values may be preceded by a character indicating the
                  operation to be performed, as follows:

                  =    The value from the file must equal the specified value.

                  <    The value from the file must be less than the specified

                  >    The value from the file must be greater than the speci‐
                       fied value.

                  &    All the bits in the specified value must be set in  the
                       value from the file.

                  ^    At  least  one  of the bits in the specified value must
                       not be set in the value from the file.

                  x    Any value will match.

                  If the character is omitted, it is assumed to be "=".

                  For comparison of numeric values, the sign and size of  both
                  the  value in the file and the value from the value field of
                  the magic entry will match that of  the  corresponding  type
                  field.  If  there  is a non-zero mask (&) in the type field,
                  the comparison will be unsigned.

                  For string values, the byte string from the file must  match
                  the  specified  byte  string.  The byte string from the file
                  which is matched is the same length as  the  specified  byte
                  string. If the value is a string, it can contain the follow‐
                  ing sequences:

                  \character     The backslash-escape sequences  \\,  \a,  \b,
                                 \f, \n, \r, \t, \v.

                  \octal         Octal sequences that can be used to represent
                                 characters with  specific  coded  values.  An
                                 octal  sequence  consists of a backslash fol‐
                                 lowed by the longest sequence of one, two, or
                                 three octal-digit characters (01234567).

       message    The message to be printed if the comparison succeeds. If the
                  string contains a printf(3C) 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. A line which begins with the character ">"
       indicates additional tests and messages to be printed. If the  test  on
       the line preceding the first line with a ">" succeeds, the tests speci‐
       fied in all the subsequent lines beginning with ">" are performed,  and
       the messages are printed if the tests succeed. The next line which does
       not begin with a ">" terminates this.


       file(1), printf(3C)

       In Solaris 9 and prior releases, the file utility  may  have  performed
       unsigned  comparisons for types byte, short, and long. Old user-defined
       magic files, which were specified with the -m option, will need modifi‐
       cation of byte, short, and long entries to their corresponding unsigned
       types (ubyte, ushort, or ulong) for those entries for which all of  the
       following are true:

           o      The entry uses the "<" or the ">" operator.

           o      The type field does not contain a non-zero mask.

           o      The intention of the entry is to test unsigned values.

       For  example, if the following entry is expected to match any non-zero,
       one-byte value from the file, including values for which the  sign  bit
       is on:

         #offset type    value   message
         0       byte    >0      this matches any non-zero value

       then that entry should be changed to:

         0       ubyte    >0     this matches any non-zero value

       In  Solaris  7  through  Solaris  9, when applying tests for magic file
       entries whose type field is the numeric type  "short"  or  "long",  the
       file  utility in the x86 environment would switch the byte order of the
       numeric values read. Starting in Solaris 10, the byte order will not be
       switched on x86. A test for a numeric value whose byte order is identi‐
       cal in both little- and big-endian architectures may require two  magic
       file  entries,  to  ensure  that the test correctly identifies files in
       both environments. For example, a magic file entry that will match on a
       big-endian system may look like this:

         0       long      0xf00000ff      extended accounting file

       Its  corresponding magic file entry that will match the same value on a
       little-endian system would look like this:

         0       long      0xff0000f0      extended accounting file

       There should be more than one level of subtests, with the  level  indi‐
       cated by the number of '>' at the beginning of the line.

Oracle Solaris 11.4               6 Feb 2004                          magic(5)
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