Category : Files from Magazines
Archive   : DDJ8705.ZIP
Filename : DUNCLST.LST

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Listing 1
;
; GETDIR.ASM --- set environment variable DIR = current directory path
;
; Copyright (C) 1986 Daniel Briggs
;
; This program illustrates a means of providing string functions
; to batch files. In this case, the program will set the value of
; the environment variable DIR to be the current default directory.
; This value can then be referenced later in a batch file by
; using the phrase %DIR%. The undocumented hook into the current
; copy of the command processor, int 2eh is used to do the set.
;
; To assemble, link, and convert to an executable COM file:
;
; MASM GETDIR;
; LINK GETDIR;
; EXE2BIN GETDIR.EXE GETDIR.COM
;

stk_size equ 1000h ;a good healthy stack

cseg segment para public 'CODE'
assume cs:cseg, ds:cseg, ss:cseg, es:cseg

org 2ch
env_ptr label near ;points to local environment

org 100h ;skip to the end of the PSP
DOS_entry label far
jmp set_str

parameter db 0, 'set ' ;start of command to be passed
var_name db 'DIR=' ;counted string name
var_value db 80 dup (?) ;buffer for variable value

iSP dw offset end_code + stk_size

set_str proc near
cld ;addressing already set by loader
mov sp, iSP ;set stack pointer

mov si, offset var_value
call get_value ;fill value with desired string

mov al, 0
mov cx, -1
mov di, offset parameter+1
repne scasb ; find the null
dec di ; point to it
mov byte ptr ds:[di], 0dh ; ascii CR
not cx ; create count byte
mov parameter, cl

mov bx, iSP ;top of program
mov cl, 4
sar bx, cl
inc bx
mov ah, 4ah ;es already set appropriately
int 21h ;shrink down to memory needed

mov si, offset parameter
int 2eh ;invoke the command processor

push cs ;reset stack
pop ss
mov sp, iSP ;put the stack pointer back

;
; Can you find a means of getting a status back from this technique?
;
mov ah, 4dh
int 21h ;get the returned status <**wrong**>

mov ah, 4ch ;terminate w/status
int 21h
set_str endp

comment /
This is the routine that actually sets the value of the
string. In this example, it sets the buffer pointed to
by DS:SI to the current pathname. What ever string is set
must be terminated by a null. The procedure
assumes that the buffer starts initialized to 0s, so does
not add the final null.
/

get_value proc near
mov byte ptr ds:[si], '\' ;not provided by DOS
inc si
mov ah, 47h
mov dl, 0
mov di, si
int 21h ; get current directory
ret
get_value endp

end_code label near

cseg ends

end DOS_entry
 mov byte ptr ds:[si], '\' ;not provided by DOS
inc si
mov ah, 47h
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