Changing Unix environment within a C program

[akn846]

I am trying to port a Korn shell program across to C on a Unix platform.

As part of this program, I need to be able to change the working directory within the C program. I have found the getenv/putenv functions according to the Wrox Beginning Linix programming book.

Whilst I understand that any changes to the Unix environment made within the code will not be seen by the calling Unix process, I have included a call to the system function in order to get the (intended to be the changed) directory - but this program just reports the same directory as when the program started?

Can someone explain what I am doing wrong/or mis understanding.

Below appears the code in question:

#include <stddef.h>
#include <stdlib.h>

extern char **environ;

main (int argc, char *argv[])
{

int RCODE;

RCODE=putenv(&quot;PWD=/tmp&quot;
system(&quot;pwd&quot;
if (RCODE != 0)
return (-1);
else
return 0;
}
Thanks

Andy

 

[Kenrae]

system call execs a new shell, with its own environment. It's like a new login, it reads .profile file.

 

[akn846]

Kenrae

Thanks for this - I did know this, honest!, but having got so excited about learning about putenv/getenv I obviously forgot about it!

Whats the best code I can use to prove that the environment is being changed then?

Regards

Andy

 

[Kenrae]

How about a getenv() and writing it to stdout?
You can always execute a pwd using exec call. Like:

execl("pwd","pwd",0);

 

[akn846]

Thanks again - redirect getenv to stdout?! Please!!!!

 

[Kenrae]

Where do you see the word &quot;redirection&quot;?
I thought on something like that:

st=getenv("PWD");
write(stdout,st,strlen(st));

 

[Kenrae]

Oh, and another thing. It's

execl("/bin/pwd","pwd",0);

 

[akn846]

Ken

Thanks - but when I use the command about for writing out the information - stdout is not defined on the Dynix system.

Also, I used the execl command you provided above - but the directory reported is the same one as before the program started - whereas I would expect it to be reporting the /tmp directory.

Cheers

 

[Kenrae]

If stdout is not defined, include stdio.h or write to 1.

It seems that exec calls don't inherit your environ. Try man exec, there should be a way to do it.

 

[akn846]

Ken

Thanks for all your help, changing the stdout to 1 worked a treat!

Thanks again

andy