Usage: 24swap [options] file ...
Swaps bytes pairs and/or quadruples on the files listed.
 -q            Operate quietly
 -pattern pat  'pat' determines the pattern of 2 and 4
                 byte swaps.  Each element is of the form
                 2xN or 4xN, where N is the number of
                 bytes to swap as pairs (for 2x) or
                 as quadruples (for 4x).  For 2x, N must
                 be divisible by 2; for 4x, N must be
                 divisible by 4.  The whole pattern is
                 made up of elements separated by colons,
                 as in '-pattern 4x39984:2x0'.  If bytes
                 are left over after the pattern is used
                 up, the pattern starts over.  However,
                 if a byte count N is zero, as in the
                 example below, then it means to continue
                 until the end of file.

 N.B.: You can also use 1xN as a pattern, indicating to
         skip N bytes without any swapping.
 N.B.: A default pattern can be stored in the Unix
         environment variable AFNI_24SWAP_PATTERN.
         If no -pattern option is given, the default
         will be used.  If there is no default, then
         nothing will be done.
 N.B.: If there are bytes 'left over' at the end of the file,
         they are written out unswapped.  This will happen
         if the file is an odd number of bytes long.
 N.B.: If you just want to swap pairs, see program 2swap.
         For quadruples only, see program 4swap.
 N.B.: This program will overwrite the input file!
         You might want to test it first.

 Example: 24swap -pat 4x8:2x0 fred
          If fred contains 'abcdabcdabcdabcdabcd' on input,