Opens an existing file or creates a new file.  If you do not
  explicitly open a file before accessing it, the file is created
  (for write operations) or opened with default attributes.

     OPEN (par[,par]...)

     par  Is a keyword specification in one of the
          following forms:

          keywd
          keywd=value

          keywd  Is a keyword.  (See the subtopic headings
                 listed at the end of this Help topic.)
          value  Is a keyword value. (Some keywords do not
                 have keyword values.)

  If an OPEN statement is executed for a unit that is already open,
  and the file pathname (or specification) is different from that of
  the current open file, the previously opened file is closed and the
  new file is opened.  If the file pathname (or specification) is the
  same for both files, the new value of the BLANK= specifier is in
  effect, but the position of the file is unaffected.

  Keyword specifications can appear in any order.  In most cases,
  they are optional.  Default values apply in their absence.  If the
  logical unit specifier is the first parameter in the list, the UNIT
  keyword is optional.

  You can specify character values at run time by substituting a
  general character expression for a keyword value in the OPEN
  statement.  The character value can contain trailing spaces but not
  leading or embedded spaces; for example:

     CHARACTER*6 FINAL /' '/
     ...
     IF (exp) FINAL = 'DELETE'
     OPEN (UNIT=1, STATUS='NEW', DISP=FINAL)

                                 NOTE

          Keyword values that are numeric expressions can  be
          any  integer  or real expression.  The value of the
          expression is converted to integer data type before
          it is used in the OPEN statement.