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Rev 353 Rev 366
Line 28... Line 28...
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; input buffer used for the "previous command" history
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; input buffer used for the "previous command" history
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BUF000 db 128, 0 ; +0Ch
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BUF000 db 128, 0 ; +0Ch
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BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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- 
 
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; offset of the COMSPEC variable in the environment block, 0 means "use
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; boot drive". this value is patched by the transient part of COMMAND.COM
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COMSPECPTR dw 0  ; +8Eh
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; fallback COMSPEC string used if no COMPSEC is present in the environment
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; drive. drive is patched by the transient part of COMMAND.COM
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COMSPECBOOT db "@:\COMMAND.COM", 0 ; +90h
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skipsig:         ; +8Eh
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skipsig:         ; +9Fh
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; set up CS=DS=SS and point SP to my private stack buffer
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; set up CS=DS=SS and point SP to my private stack buffer
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mov ax, cs
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mov ax, cs
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mov ds, ax
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mov ds, ax
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mov es, ax
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mov es, ax
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mov ah, 0x4D
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mov ah, 0x4D
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int 0x21
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int 0x21
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xor ah, ah          ; clear out termination status, I only want the exit code
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xor ah, ah          ; clear out termination status, I only want the exit code
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mov [LEXCODE], ax
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mov [LEXCODE], ax
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- 
 
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; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)
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mov dx, COMSPECBOOT
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; do I have a valid COMSPEC?
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or [COMSPECPTR], word 0
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jz USEDEFAULTCOMSPEC
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; set ES:DX to actual COMSPEC
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mov es, [ENVSEG]
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mov dx, [COMSPECPTR]
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USEDEFAULTCOMSPEC:
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; prepare the exec param block
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; prepare the exec param block
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mov ax, [ENVSEG]
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mov ax, [ENVSEG]
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mov [EXEC_PARAM_REC], ax
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mov [EXEC_PARAM_REC], ax
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mov ax, COMSPEC
 - 
 
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mov [EXEC_PARAM_REC+2], ax
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mov [EXEC_PARAM_REC+2], dx
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mov [EXEC_PARAM_REC+4], ds
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mov [EXEC_PARAM_REC+4], es
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; execute command.com
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; execute command.com
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mov ax, 0x4B00         ; DOS 2+ - load & execute program
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mov ax, 0x4B00         ; DOS 2+ - load & execute program
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push es                ;
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pop ds                 ;
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mov dx, COMSPEC        ; DS:DX  - ASCIZ program name TODO: use real COMSPEC...
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;mov dx, COMSPEC       ; DS:DX  - ASCIZ program name (preset already)
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push cs
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pop es
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mov bx, EXEC_PARAM_REC ; ES:BX  - parameter block pointer
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mov bx, EXEC_PARAM_REC ; ES:BX  - parameter block pointer
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int 0x21
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int 0x21
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; if all went well, jump back to start
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; if all went well, jump back to start
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jnc skipsig
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jnc skipsig
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- 
 
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; restore DS=CS
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mov bx, cs
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mov ds, bx
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; update error string so it contains the error number
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; update error string so it contains the error number
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add al, '0'
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add al, '0'
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mov [ERRLOAD + 4], al
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mov [ERRLOAD + 4], al
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; display error message (with trailing COMSPEC)
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; display error message
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mov ah, 0x09
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mov ah, 0x09
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mov dx, ERRLOAD
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mov dx, ERRLOAD
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mov [COMSPCZ], byte '$' ; patch comspec terminator to be $
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int 0x21
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int 0x21
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mov [COMSPCZ], byte 0   ; restore initial (NULL) compsec terminator
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; wait for keypress
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; wait for keypress
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mov ah, 0x08
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mov ah, 0x08
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int 0x21
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int 0x21
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;     +2     4   address of command line to place at PSP:0080
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;     +2     4   address of command line to place at PSP:0080
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;     +6     4   address of an FCB to be placed at PSP:005c
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;     +6     4   address of an FCB to be placed at PSP:005c
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;    +0Ah    4   address of an FCB to be placed at PSP:006c
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;    +0Ah    4   address of an FCB to be placed at PSP:006c
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EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
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EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
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ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM FROM:", 13, 10
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ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'
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 - 
 
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COMSPEC db "C:\SVN\SVARDOS\SVARCOM\COMMAND.COM"
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COMSPCZ db 0
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; FreeDOS int 21h functions that I use require at least 32 bytes of stack,
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; DOS int 21h functions that I use require at least 32 bytes of stack, here I
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; here I allocate 64 bytes to be sure
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; allocate 64 bytes to be sure
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STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
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STACKPTR db "xx"
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STACKPTR db "xx"