gangwani@andromeda.rutgers.edu.rutgers.edu (Sunil Gangwani) (11/25/90)
Hi,
With the system() function call a new shell is executed in
DOS or UNIX. I would like the set an environment variable from
inside a program so that the variable exists when I exit the
program??
Ex. in DOS
system("set var=Hello");
The above will not work because a new command.com is executed
and exited immediately. How can I overcome this simple problem??
Please respond directly to gangwani@andromeda.rutgers.edu because
due to heavy traffic our facility removes USENET stuff every two
days...
thanks in advance
Sunil Gangwaniherrj@valnet.UUCP (Jonathan R. Herr) (11/27/90)
gangwani@andromeda.rutgers.edu.rutgers.edu (Sunil Gangwani) writes: > > Hi, > > With the system() function call a new shell is executed in > DOS or UNIX. I would like the set an environment variable from > inside a program so that the variable exists when I exit the > program?? > > Ex. in DOS > > system("set var=Hello"); > > The above will not work because a new command.com is executed > and exited immediately. How can I overcome this simple problem?? Well, you don't say what C you're using. But, there is a way to set environment variables in Turbo C 2.0 by use of the putenv(const char *name) command. It is also availble on Unix systems according to the reference guide. Something like this might work: /* ========================================== */ #include <stdlib.h> putenv("set var=Hello"); /* ========================================== */ My syntax may be off base. I'm not super-experienced in C like some of these folk. I only know this much as I've been using getenv() to access some environment variables for a program I've been writing for Waffle BBS in which I have to locate a definition file that is defined as an environment variable and I saw the reference to putenv(). > Please respond directly to gangwani@andromeda.rutgers.edu because > due to heavy traffic our facility removes USENET stuff every two > days... I'll forward it to you. > Sunil Gangwani Jon Herr ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |Jonathan R. Herr (aka Jon) | herrj@silver.ucs.indiana.edu | | | herrj@valnet.UUCP | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
jwindley@matt.ksu.ksu.edu (Jay Windley) (11/28/90)
Assuming pg means "program" here's an answer: In UNIX the environment is changed with the putenv(3) function. You pass it a pointer to a string of the format <var>=<value> (e.g., "HOME=/usrc/foo"). The caveat here is that the string must be stored in static memory; either a global or a static character array. Note that this only changes the environment of the current process, not its parent. There is no way under UNIX for a process to change the environment of its parent, since the environment it receives upon invocation is merely a copy of its parent's. Children of the process will receive the altered evironment if they are spawned after the change. -- Jay Windley - CIS Dept. - Kansas State University NET: jwindley@matt.ksu.ksu.edu VOICE: (913) 532-5968 FAX: (913) 532-6722 USnail: 323 Seaton Hall, Kansas State Univ., Manhattan, KS 66506 Obligatory quote: "" -- /dev/null
carroll@cs.uiuc.edu (Alan M. Carroll) (11/28/90)
Here is how you set environment variables in a parent shell in UNIX:
Let us say you have a program named "bob" that wants to set environment
variables. Under sh you would write a function like
dave() { eval `bob` ; }
Under ksh or csh, you would use an alias. The bob program then generates
output that looks like
VAR=VALUE
VAR2=VALUE2
...
for sh or ksh, and some bizarro-nonsense format that may or may not have an
"=" sign in it for csh.
You then use "dave" instead of "bob" to set the variables. "bob" in effect
generates commands for the shell, and "dave" causes the shell to execute them.
--
Alan M. Carroll "It's psychosomatic. You need a lobotomy,
Epoch Development Team I'll get a saw."
CS Grad / U of Ill @ Urbana ...{ucbvax,pur-ee,convex}!cs.uiuc.edu!carrollturbo@evax.arl.utexas.edu (Chris Turbeville) (11/29/90)
Functions like putenv (getenv, etc...) are available for most all compilers but they do not set the parents environment just the programs. I could be off base for some compilers but I know MSC sets only its COPY of the environment not its parents. Chris