HERE IS THE OLD ROUTINE - DOESN'T PROPERLY SET UP ES FOR SCASB:
check_command_string proc near
push di
cld;Check for first quotation mark -
mov al,'"'; replace with null (20h) if present.
mov di,82h;Command tail starts at 82h.
xor ch,ch
mov cl,byte ptr ds:[080h];Length of command tail stored at 80h
repne scasb
jcxz end_check
mov byte ptr [di-1],20h

std;Change direction & check for
add di,cx; last quotation mark.
dec di
dec di
repne scasb
jcxz end_check
mov byte ptr [di+1],20h

end_check:
cld
pop di
ret
check_command_string endp



HERE IS THE NEW ROUTINE - DOES PROPERLY SET UP ES
;-------------------------------------------------------------------------------;Check_command_string removes first & last quotation marks from command
;string. This lets xcall pass redirection request to COMMAND.COM. This
;routine saves ES & DI.
;-------------------------------------------------------------------------------
check_command_string proc near
push di
push es
mov ax,ds
mov es,ax

xor ch,ch
mov cl,byte ptr ds:[080h];Length of command tail stored at 80h
jcxz end_check;All done if no command tail
cld;Check for first quotation mark -
mov al,'"'; replace with null (20h) if present.
mov di,82h;Command tail starts at 82h.
repne scasb
jnz end_check
mov byte ptr [di-1],20h

std;Change direction & check for
add di,cx; last quotation mark.
dec di
dec di
repne scasb
cld
jnz end_check
mov byte ptr [di+1],20h

end_check:
pop es
pop di
ret
check_command_string endp