SHELL BEXP,VAR,SEXP1,SEXP2

 Function
  Shell out to a program or batch file.

 Syntax
  SHELL viacc,retcode,prog,cmds

   viacc    - A boolean expression with value TRUE if the shell should
              be made via COMMAND.COM; FALSE if it should be shelled to
              directly.
   retcode  - A variable in which to store the return code.
   prog     - A string expression with the file name to shell to.
   cmds     - A string expression with any arguments to pass to prog.

      (NOTE:  If viacc is TRUE, the value assigned to retcode will be the
              return code of COMMAND.COM, not prog)

 Remarks
  You may have have need to run a COM, EXE or BAT file from your PPE.  You
  may need to do this to simulate running a DOOR or to access some service
  not normally available from PCBoard or PPL.  This function will allow
  you to do that.  If the viacc parameter is TRUE (you want COMMAND.COM to
  load the specified file) then your PATH environment variable will be
  searched for prog if it isn't in the current directory or isn't fully
  qualified (path and extension) as though you had entered it on the
  command line.  If viacc is FALSE then you must specify the path and
  extension of the program to run.  Additionally, the retcode variable
  will only be meaningful if viacc is FALSE.

 Examples
  INTEGER rc
  SHELL TRUE,rc,"DOOR",""

  INTEGER rc
  STRING p,c
  LET p = "DOORWAY.EXE"
  LET c = "com2 /v:dO /m:600 /g:on /o: /k:v0 /x: /c:dos"
  SHELL FALSE,rc,p,c