Indicates a default file specification string.  It takes the
  following form:

  DEFAULTFILE = ce

  ce  Is a character expression.

  This specifier supplies a value to the RMS default file
  specification string for the missing components of a file
  specification.  If you do not specify the DEFAULTFILE keyword,
  Fortran uses the default value 'FORnnn.DAT', where nnn is the unit
  number with leading zeros.

  The default file pathname string is used primarily when accepting
  file specifications interactively.  File specifications known to a
  user program are normally completely specified in the FILE keyword.

  You can specify default values for any one of the following file
  specification components:  node, device, directory, file name, file
  type, and file version number.

  When you specify any of the above components in the FILE keyword,
  they override those values specified in the DEFAULTFILE keyword.

  The following example uses the file name supplied by the user and
  the default file specification supplied by the DEFAULTFILE keyword
  to define the file specification for an existing file:

     TYPE *, 'ENTER NAME OF DOCUMENT'
     ACCEPT *, DOC
     OPEN (UNIT=1, FILE=DOC, DEFAULTFILE='[ARCHIVE].TXT',
    1     STATUS='OLD')