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; Example of how to use the EXEC function

c_start:
	jmp start      


fcb1	: db 40 dup 0
fcb2	: db 40 dup 0

parmblk: dw 0                 ; Segment address of environment string
         dd 0                 ; Pointer to command line
	 dd 0		      ; Pointer to default FCB to be passed at PSP+5CH
	 dd 0                 ; Pointer to default FCB to be passed at PSP+6CH


;cmdline: db 6,'/C mn',13
cmdline: db 0

stackspace db 512 dup 0
newstack: dw 0
com_spc : db 'COMSPEC=',0              ;Compare string
com_val: db 128 dup 0                  ;Buffer for COMSPEC value

start:
	push ds
	mov ds,w[02C]			;Fetch environment
	mov si,0

one_more:
	es mov di,com_spc

l1:					;Compare strings
	cmpsb
	je l1

	sub si,1
	es cmp di,com_val               ;All characters match?

	je getval                       ;Yes, fetch value of COMSPEC

next:
	inc si                          ;Search for next environmental variable
	ds cmp b[si],0                   
	jne next
        inc si
	ds cmp b[si],0
	jne one_more
	

getval:                                 
	movsb	
	ds cmp b[si-1],0
	jne getval	

	pop ds
	
	mov bp,parmblk
	mov [bp+2],cmdline
	mov [bp+4],CS

	mov [bp+6],fcb1
	mov [bp+8],CS
	mov [bp+10],fcb2
	mov [bp+12],CS

	mov SP,newstack

	mov ah,4AH            ; Mshrink, shrink memory
	mov bx,c_end-c_start
	mov es,cs             ; shrink Code Segment
	int 21H

	mov ah,4BH            ; EXEC
	mov al,00H            ; Load and Execute
	mov dx,com_val
        mov bx,parmblk
	int 21H     	
	
	mov ax,04c00
	int 21H

c_end:
.

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