Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!orca!javelin.es.com!bgeer
From: bgeer@javelin.es.com (Bob Geer)
Newsgroups: comp.lang.pascal
Subject: Re: Change ENV.
Message-ID: <1991Jan14.143941.10541@javelin.es.com>
Date: 14 Jan 91 14:39:41 GMT
References: <25474@adm.brl.mil>
Reply-To: bgeer%javelin@dsd.es.com
Organization: Evans & Sutherland Computer Corp., Salt Lake City, Utah
Lines: 62

ZCCBJSB%EB0UB011.BITNET@cunyvm.cuny.edu ( Info-Pascal list) writes:


>Has anyone some code/idea to modify PERMANENTLY a DOS environtment
>variable from a TP program (any TP version)?

Each program run gets a new copy of the environment of the current
program.  For example, any changes to the environment of, say, a batch
program doesn't make its way to the previous copy so is lost when the
batch program terminates.  Those changes only propogate to programs
run from the batch file, or programs they subsequently run.

Dr. Dobb's Journal #122 (December 1986) contained an article about
MS-DOS' undocumented interrupt 2Eh which will change the `master' copy
of the environment but not any copies already propogated from it.
Below I've included a procedure fragment that I use to edit the path
string.

The string handed to 2Eh must be formatted in the DOS style: length
byte, string, <CR>, <NULL>.  The environment must be sufficiently
large to accept the string; I found I had to limit my path string to
127 bytes (with standard size environment space) to prevent hanging
DOS.  This has worked for me from DOS 2.0 thru DOS 4.01, but MS
doesn't guarantee undocumented interrupts.  I didn't want to soak up
bandwidth by including the whole program, & I'm unsure of my ability
to send or receive e-mail.

---------------------------------------
	{ new_path is type PATH, defined as follows: }
	PATH = RECORD
	  CASE BOOLEAN OF
	    TRUE  : (str   : STRING[255]) ;
	    FALSE : (bytes : ARRAY [0..255] OF BYTE) ;
	  END ; { path }

	{ MY_SP, MY_SS, TMPDS, TMPSI are integers }

         new_path.str := CONCAT('SET ', path_str.str) ;
         new_path.bytes[1+LENGTH(new_path.str)] := CARRIAGE_RETURN ;
         new_path.bytes[2+LENGTH(new_path.str)] := NULL ;
         WRITELN ('Setting path to:') ;
         WRITELN (new_path.str) ;
         TMPDS := SEG(new_path) ; { path command segment for dos }
         TMPSI := OFS(new_path) ; { path command offset  for dos }
         INLINE ($1E/                 { push ds ; save environment }
                 $55/                 { push bp ;   " }
                 $2E/$8E/$1E/TMPDS/   { mov ds,cs:TMPDS ; prepare for fn }
                 $2E/$8B/$36/TMPSI/   { mov si,cs:TMPSI }
                 $2E/$8C/$16/MY_SS/   { mov cs:MY_SS,ss ; save stack seg }
                 $2E/$89/$26/MY_SP/   { mov cs:MY_SP,sp ; & stack ptr }
                 $CD/$2E/             { int 2e ; call msdos }
                 $2E/$8E/$16/MY_SS/   { mov ss,cs:MY_SS }
                 $2E/$8B/$26/MY_SP/   { mov sp,cs:MY_SP }
                 $5D/                 { pop bp }
                 $1F) ;               { pop ds }
	{ continue pascal code here }
----------------------------------------
-- 
<> Bob `Bear' Geer <>               bgeer@javelin.sim.es.com              <>
<>      Alta-holic <>   speaking only for myself, one of my many tricks   <>
<> Salt Lake City, <>    "We must strive to be more than we are, Lal."    <>
<>          Ootah  <>           -- Cmdr. Data, learning schmaltz          <>