name  set_env
COMMENT;------------------------------------------------------
Purpose: to write directly to the original environment using 
undocumented interrupt number 2Eh - For command line usage: 
set_env string_name Revised/Reassembled Under MASM v.5.0 03/02/88 
- Ron Schroeder First assemble, link and then use EXE2BIN to 
convert to .com file   

;-----------------------------
code_seg       segment
               assume cs:code_seg, ds:code_seg,es:code_seg,ds:code_seg
               org       100h           ; com file format

main           proc      near

               jmp       short  START   ;skip over data area
       
;----------------------------------------------------------------

set            db        ODh            ; chars in `SET STRING=` (11)
               db        'SET STRING='  ;environmental literal
setting        db        20h   dup(0)   ;arbitrary size envp buffer
;----------------------------------------------------------------

START:         mov       ah,4Ah         ; first modify memory location
               mov       bx,offset FREE ; make room for command.com
               dec       bx
               mov       cl,o4h
               shr       bx,cl
               inc       bx
               int       21h            ; do it

               xor       ch,ch          ; zero out ch (defensive move
               mov       si,0080h       ; get command line length
               mov       cl,byte ptr[si]; put it in cl
               dec       cl             ; adjust it
               jcxz      ERROR1         ; error if no command line    
               add       set,cl         ; add cmd line size to literal
               mov       si,0082h       ; beginning of command line
               mov       di,offset setting  ; destination 
               rep       movsb          ; put all in setting for length
                                        ; in cx
               xor       bh,bh          ; zero out bh (defensive move)
               mov       bl,set         ; 'new' length of env string
               mov       set[bx][1],0Dh ;0Dh is cr at end of string
               mov       si,offset set
               int     2Eh              ; write ds:si to original environment
               
               xor      al,al          ; zero out al for zero error code ret 

EXIT:          mov       ah,4Ch         ; quit
               int       21h

ERROR1:        mov       al,01h         ; if no characters entered
               jmp       short EXIT     ; then error

FREE           label     byte           ; to determine memory
                                        ; allocation for this program
main           endp                     ; end of procedure

;----------------------------------------------------------------

code_seg       ends
               end       main