marc@ur-univax.UUCP (03/11/85)
The DOS manual talks about adding things to the environment with the SET
ENVIRONMENT command and goes on to say that things in the environment can be
accessed from within an application. Can anyone tell me how to do this or
where it is documented ?
Mark J. Dumic
...!{allegra|decvax|seismo}rochester!ur-univax!marcjchapman@watcgl.UUCP (john chapman) (03/13/85)
> The DOS manual talks about adding things to the environment with the SET > ENVIRONMENT command and goes on to say that things in the environment can be > accessed from within an application. Can anyone tell me how to do this or > where it is documented ? > > Mark J. Dumic > ...!{allegra|decvax|seismo}rochester!ur-univax!marc This works the same way is in unix, e.g. set <name>=<string> (I can't recall off hand if the = is necessary or just a blank but you get the idea. Accessing the environment is a different matter: when a program is executed part of the run time header (in first 100h bytes of programs code segment) is set to the address of the environment. The environment is stored as a series of strings x=y. So you would need some sort of routine to pick up the pointer and scn through the environment looking for the string of interest (I think they are all null terminated). Hope this is what you were looking for, John Chapman ...!watmath!watcgl!jchapman
shor@sphinx.UChicago.UUCP (Melinda Shore) (03/14/85)
[] >From: marc@ur-univax.UUCP >The DOS manual talks about adding things to the environment with the SET >ENVIRONMENT command and goes on to say that things in the environment can be >accessed from within an application. Can anyone tell me how to do this or >where it is documented ? Check out the section of the manual on the DOS program segment. Basically, the "environment variables" are strings (both identifiers and values) in memory, the beginning address of which is located at offset 2C of the program segment prefix of the program starting up. When a program starts up, DS and ES point to the program segment prefix. As I recall, DS tells us which segment, ES the address within the segment. -- Melinda Shore University of Chicago Computation Center uucp: ...!ihnp4!gargoyle!sphinx!shor Mailnet: staff.melinda@uchicago.mailnet Bitnet: shor%sphinx@uchicago.bitnet ARPA: staff.melinda%uchicago.mailnet@mit-multics.arpa
gbs@voder.UUCP (George Smith) (03/15/85)
> The DOS manual talks about adding things to the environment with the SET > ENVIRONMENT command and goes on to say that things in the environment can be > accessed from within an application. Can anyone tell me how to do this or > where it is documented ? > > Mark J. Dumic > ...!{allegra|decvax|seismo}rochester!ur-univax!marc The following procedure for Turbo Pascal illustrates how to use this very powerful feature in MS-DOS. Look at the description of the exec function and the description of the PSP (Program Segment Prefix) in the DOS Technical Ref manual and the SET command description in the DOS manual for more info. Hope this helps. (* ** The following function will look for an environment variable ** and return it's definition if found. If the variable is not ** found, then the returned definition variable will be empty. ** Compiled and run with Turbo Pascal v2.0 on an IBM PC/XT running ** PC-DOS v2.1. ** ** This code is entered into the Public Domain for free use by all. ** George B. Smith, March 15, 1985. *) { type mstring = string[255]; } procedure GetEnvParam(name: mstring; { environment variable to search for } var param: mstring { returned definition } ); var envseg: integer; { segment address of environment from PSP } ei: integer; { index into environment } envname: mstring; { current environment string name } ch: char; { current character from environment } found: boolean; { if true then environment name was found } begin envseg := MemW[CSeg:$2C]; { get address of environment from PSP } found := FALSE; ei := 0; ch := chr(Mem[envseg:ei]); { get first char from environment } while (ch <> chr(0) and (not found) do begin envname := ''; while ch <> '=' do begin { get environment string name } envname := envname + ch; ei := ei + 1; ch := chr(Mem[envseg:ei]) end; ei := ei + 1; { skip over the EQUALS } param := ''; ch := chr(Mem[envseg:ei]); while ch <> chr(0) do begin { get environment string parameter } param := param + ch; ei := ei + 1; ch := chr(Mem[envseg:ei]) end; if name = envname then { check for a match } found := TRUE; ei := ei + 1; ch := chr(Mem[envseg:ei]) end; if not found then param := '' end; -- George B. Smith National Semiconductor ...!{ihnp4!nsc | decvax!decwrl!nsc | ucbvax}!voder!gbs
bill@absolut.UUCP (03/16/85)
>The DOS manual talks about adding things to the environment with the SET >ENVIRONMENT command and goes on to say that things in the environment can be >accessed from within an application. Can anyone tell me how to do this or >where it is documented ? >Mark J. Dumic >...!{allegra|decvax|seismo}rochester!ur-univax!marc >---------- I don't know about DOS 2.xx but in DOS 3.0 you can use the ENVIRON and ENVIRON$ commands in basic to access environment variables. Sorry, that I can't be of more help. William Gibbs {ucbvax!cbosgd!ima!cfib, decvax!cca}!absolut!bill Absolut Software 617-232-8377 2001 Beacon Street Boston, MA 02146-4227
manis@ubc-cs.UUCP (Vince Manis) (03/18/85)
A pointer to the current environment variables is stored in the segment prefix. I think that the offset is $5c, but I don't have my DOS technical reference in front of me. The environment consists of a sequence of strings, each terminated by a null byte ($00). The last string is followed by a second null. Each string consists of a variable name, an equal sign, and a string. There's no limitation other than a total environment limitation of 32K. Thus to find the value of a given variable, simply search the environment for a string beginning with the variable name followed by an equal sign. A recent issue of PC Tech Journal had a package of Turbo Pascal routines for doing DOS things. I didn't read the article carefully, but I believe there was an example routine there.
lauren@vortex.UUCP (Lauren Weinstein) (03/20/85)
While the theoretical limit on environment strings may be 32K, it turns out that in 2.X (and I believe in 3.X as well) you can't pass more than 128 bytes of environment down from autoexec to the rest of the system. Unfortunately, this tends to be exactly the use you most often want to make. --Lauren--