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From:
[email protected] (Dan Carson)
Subject: Re: Setting DOS variables. HELP!
Message-ID: <
[email protected]>
Organization: John Fluke Mfg. Co., Inc., Everett, WA
References: <lsloan.740685627@nova> <
[email protected]>
Distribution: na
Date: Fri, 25 Jun 1993 17:16:02 GMT
Lines: 48
In article <
[email protected]>
[email protected] (AT5 Holger Heimann) writes:
>Lance Sloan (
[email protected]) wrote:
>
>: I am able to read DOS environment variables, but I am having trouble
>: setting the variables to new values. I am using Perl v4.0 pl19.
>
>: I make sure I have a DOS variable set before I run the program so that
>: I can be sure there is enough memory to hold the new value. In the
>: program the variable contains the new value, but as soon as perl exits
>: the variable goes back to it's original value. ...
>
>As far as I remember DOS (like UNIX) inherits the spawning processes
>environment to the child. In your case command.com calls perl, which
>gets an exact *copy* of command.com's environment. Everything you change
>now will only concern perls environment. After perl exits it is
>discarded from memory with its (modified) environment and the old
>environment becomes active again.
>This is a feature, not a bug.
>By the way: No way to say 'system("set XX=yy")' or the like. You would
>just spawn another command.com and even perl wouldn't see any change in
>it's environment, not to talk about the original shell.
>
>There are (complicated) ways to circumvent this, but I cannot remember them.
>(You have to trace memory-control-block to the parent and seek for its
>environment, I guess)
>
>Correct me someone if I was wrong.
>
>hh
A batch file doesn't spawn a subprocess, so you could wrap your perl in
a .bat :
prog.bat: prog.pl:
----------- ----------
perl prog.pl open(A,">blat.bat");
blat print A "set foo=bar\n";
del blat.bat close(A);
I tried this, it works on DOS. This doesn't work on UNIX, but there is a
similar trick in csh using alias and eval `script`.
--
Dan Carson
[email protected]
John Fluke Mfg.
Everett, WA
