🚀 go-pugleaf

Grant Slender <grants@comtech.com.au> wrote:

>I need to get the list of current environment variables in a Dos based C
>program....I can do that using the "main( " argument lists....

>But how do I write a changed value back???

>Thanks for any tips

An example program

cseg	segment
;1) Getting all environment vars

;A simple program which uses the stdlib from Rhyde en co..
;include	stdlib.inc; that is both all includes and the shell..

print
db	'Display of environment vars ',cr,lf,cr,lf,0

;get ptr to psp
mov	ah,	62h	;stdlib sets es to dgroup on startup
int	21h		;normally es points to PSP at startup	
mov	es,	bx
;get ptr to env
mov	bx,	es:[2Ch]	es:[0] points to your PSP
mov	es,	bx	
xor	di,	di	es:[di] points to your environment
jmp	short	startit
printLP: mov	ah,	0eh
	int	10h
startit:	mov	al,	es:[di]
	inc	di
	or	al,	al
	jnz	printLP
	putcr
	mov	al,	es:[di]
	inc	di
	or	al,	al
	jnz	printLP
	exitPGM
	putcr

2)	Getting on environment variables value
	print
	db	'Searching for path',cr,lf,cr,lf,0
        cld                     ;forward search
        mov     al,     '='
        mov     dx,     di      ;di points to end of environment
        xor     di,     di
        mov     cx,     dx      ;set cx to len environ first
searchLP:
        repnz   scasb
        jnz     notfound
        mov     bx,     di      ;save di
        mov     cx,     env_var_len
        sub     di,     cx
        lea     si,     env_var
        repz    cmpsb           ;compare strings
        jz      found
        mov     di,     bx      ;restore di
        mov     cx,     dx      ;restore cx
        sub     cx,     bx
        jmp     searchLP

found:  puts
        putcr
;set a specific environ variable
        print
        db      'Changed path value to ',cr,lf,cr,lf,0
        lea     si,     new_path
        mov     dx,     di      ;save di again
copyLP:	lodsb
        stosb
        or      al,     al
        jnz     copyLP
        mov     di,     dx      ;restore di
        puts
        putcr

notfound:
        exitPgm


cseg    ends
dseg    segment

env_var         db      'PATH='
env_var_len     dw      $-env_var
new_path        db      'C:\DOS\',0

dseg    ends


end     main

I did not tested this program thoroughly but it should be
enough to get you started. The environment is really
not that difficult. A few other things:

;environment variables are zero terminated in the format:
; ' NAME= ', value,0
;environment is ended with 0,0


R.Hummel has made some nice utility available for doing this
in PCmagazine as envedit. You should look for that 
maybe.

Rick