Magnum One/Magnum One (Mid-American Digital) (Disc Manufacturing).iso/d18/tpa2_a.arc/DOSEXEC.PAS

Pascal/Delphi Source File | 1991-04-28 | 5KB | 129 lines

{$M $4000,0,0}
{═══════════════════════════ DOSEXEC.PAS ════════════════════════════}
{ Usage:  Dosexec            (From Editor, just Run)                 }
{   (prompts for Program to run)                                     }
{═══════════════════════════ DOSEXEC.PAS ════════════════════════════}

{- This demonstration illustrates the use of "local" CSeg assembly   }
{- variables allocated in the 1st Block of the current Code Segment. }
{- This is a powerful but somewhat complicated technique that you    }
{- may NEVER need to use.  (It is useful for creating customized     }
{- Exec Procedures, and Interrupt Routines that can 'Chain' rather   }
{- than Iret).  For now, just run the demonstration, and keep in     }
{- the back of your mind that variables CAN be stored in the Code    }
{- segment if you should ever find it necessary.                     }

{- NOTE: this demonstration program does not parse the parameters    }
{-  into the 'default FCBs', so some programs (including diskcopy,   }
{-  format, chkdsk, etc) cannot be run directly.  However, using     }
{-  example 2 below, you can shell to DOS and run these programs.    }

{═════════════════════════════ Examples ═════════════════════════════}
{  ( <CR> signifies Carriage Return )                                }
{  1. To list a directory on a system with a bootable hard disk:     }
{      At the 'Path' prompt:         --> C:\command.com<CR>          }
{      At the 'Parameters' prompt:   --> /c dir<CR>                  }
{  2. To shell to DOS with a system disk in drive A:                 }
{      At the 'Path' prompt:         --> A:\command.com<CR>          }
{      At the 'Parameters' prompt:   --> <CR>                        }
{      ( Type   EXIT<CR>   to return to Turbo )                      }
{═════════════════════════════ Examples ═════════════════════════════}


{════════════════════════════ Exec ═════════════════════════════}
{ Execute specified Path and Command Line or return Error in    }
{ global VAR DosError.  Compatable with DOS Unit Exec Procedure }
{════════════════════════════ Exec ═════════════════════════════}
VAR DosError: Integer;
PROCEDURE Exec(Path,CmdLine: String);
VAR
{- local var addr are assigned in reverse order -}
FCB6C:   Pointer;   { Dword pointer to FCB2 (6CH in PSP) }
FCB5C:   Pointer;   { Dword pointer to FCB1 (5CH in PSP) }
CmdPtr:  Pointer;   { Dword pointer parameter string     }
EnvSeg:  WORD;      { Segment address of environment     }

PathPtr: Pointer;   { Dword pointer Path to Exec         }

BEGIN
Assemble
Jmp Begin
SaveSs Dw 0           ; Ss and Sp MUST be saved in our Code Segment
SaveSp Dw 0           ; Int $21 Function $4B does not restore them
Begin:
  Push Ds,Bp
  Mov SaveSs,Ss       ; TP&Asm automatically supplies the needed
  Mov SaveSp,Sp       ;  Cs overrides for SaveSs and SaveSp
   ;- You can code the override explicitly (Cs Mov SaveSs,Ss) if you
   ;- prefer, and you can disable Presumptions for "WYSIWYG" assembly

  Mov W CmdPtr+2,Ss   ; Save Command Line segment
  Lea AX,CmdLine
  Mov W CmdPtr,Ax     ; And offset in Parameter Block.

;- Technical Note: For String Value Parameters, Turbo 4/5 pushes
;-  a Pointer to a Copy of the String Value.  The pointer will
;-  reference either the Local Copy OR a "Packed" copy in the
;-  callers Code Segment.  Since we will be modifying the Path
;-  string (to add a zero byte), it is essential that we use
;-  the Local copy and not a Code Seg copy.  For this reason
;-  we do NOT want to use the Pointers at [Bp+4] and [Bp+8].
;-  Instead, take advantage of the fact that TP&Asm allows
;-  reference to parameters BY NAME - the resulting code is
;-  easier to understand, and Value parameters referenced by
;-  name will ALWAYS refer to a local copy in the Stack segment

  Push Ss             ; Point ES:BX to Parameter Block
  Pop Es
  Lea Bx,EnvSeg       ; Use LEA since EnvSeg is implicitly indexed (by BP)
  Mov EnvSeg,0        ; Pass a copy of the current enviroment

  Push Ss
  Pop Ds
  Lea Si,Path         ; Point DS:SI to length byte of LOCAL COPY

  Xor Ax,Ax
  Mov Al,[Si]         ; Get length
  Inc Si
  Mov Dx,Si           ; Point DS:DX to program name
  Add Si,Ax           ; Point past Last Char
  Mov b[Si],0         ; Make it AsciiZ in LOCAL COPY

  Mov Ax,4B00h        ; DOS EXEC function: al=0, ah=4Bh
  Int 21h             ; Execute
  IF NC Xor Al,Al     ; If successful (No Carry), clear error code
                      ; 'IF' is an A86 specialty, supported for compatibility
  Xor Ah,Ah

  Cli
  Mov Ss,SaveSs       ; restore our Stack
  Mov Sp,SaveSp
  Sti
  Pop Bp,Ds           ; Restore Turbo Bp and Ds
  Mov DosError,Ax     ; Store DosError AFTER restoring DS

end; {Assemble}

END; {Exec}


VAR Path,CmdLine: String;

{════════════════════ Demonstrate Exec Call ════════════════════}
BEGIN {Main Program}
  WRITELN('Path and Program to execute [e.g. C:\Command.com]');
  WRITE('--> '); READLN(Path);
  WRITELN('Parameters for executing program [e.g. /C Dir]');
  WRITE('--> '); READLN(CmdLine);
  WRITELN('Before Exec');

  Exec(Path,CmdLine);

  CASE DosError OF
    0:  WRITELN('Successful Exec');
    2:  WRITELN('File ',Path,' Not Found');
    8:  WRITELN('Not Enough Memory to Exec ',Path);
   ELSE WRITELN('Exec Failed: Dos Error ',DosError);
  END; {CASE DosError}
END.