freebsd stable - Apr 2008 - getenv in FreeBSD 7

Somewhere between FreeBSD 6.2 and 7.0 getenv has been changed to  
return a null if an environment variable is set but has no value.  I  
don't find anything anywhere in the documentation/man pages on this.   
As a result, you cannot distinguish between a variable that is not set  
and one that is set to a value of "".  Is this a bug or a feature  
change?

On Sun, Apr 06, 2008 at 02:37:06PM -0700, Doug Hardie
wrote:
> Somewhere between FreeBSD 6.2 and 7.0 getenv has been changed to return a 
> null if an environment variable is set but has no value.  I don't find 
> anything anywhere in the documentation/man pages on this.  As a result, you
> cannot distinguish between a variable that is not set and one that is set 
> to a value of "".  Is this a bug or a feature change?
I'd begin peeking here:

http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libc/stdlib/getenv.c

-- 
| Jeremy Chadwick                                    jdc at parodius.com |
| Parodius Networking                           http://www.parodius.com/ |
| UNIX Systems Administrator                      Mountain View, CA, USA |
| Making life hard for others since 1977.                  PGP: 4BD6C0CB |

On Sun, 06 Apr 2008 14:37:06 PDT Doug Hardie <bc979@lafn.org> 
wrote:
> Somewhere between FreeBSD 6.2 and 7.0 getenv has been changed to  
> return a null if an environment variable is set but has no value.  I  
> don't find anything anywhere in the documentation/man pages on this.   
> As a result, you cannot distinguish between a variable that is not set  
> and one that is set to a value of "".  Is this a bug or a feature
> change?
This is not what I see on 7.0 or -current (and it would not
be standard compliant).  Try this under /bin/sh:

cat >x.c<<EOF
#include <stdlib.h>
#include <stdio.h>
int main(int c, char**v) {
	char* a = getenv(v[1]);
	printf("%s\n", a? a : "--null--");
	return 0;
}
EOF
cc x.c
foo="" ./a.out foo	# this should return a blank line
./a.out foo		# this should return a line with --null--

If your system behaves differently  may be you can attach a
simple test that shows the bug?

On Sun, Apr 06, 2008 at 03:05:18PM -0700, Doug Hardie
wrote:
>
> On Apr 6, 2008, at 14:52, Jeremy Chadwick wrote:
>> On Sun, Apr 06, 2008 at 02:45:24PM -0700, Jeremy Chadwick wrote:
>>> On Sun, Apr 06, 2008 at 02:37:06PM -0700, Doug Hardie wrote:
>>>> Somewhere between FreeBSD 6.2 and 7.0 getenv has been changed
to return
>>>> a
>>>> null if an environment variable is set but has no value.  I
don't find
>>>> anything anywhere in the documentation/man pages on this.  As a
result,
>>>> you
>>>> cannot distinguish between a variable that is not set and one
that is
>>>> set
>>>> to a value of "".  Is this a bug or a feature change?
>>>
>>> I'd begin peeking here:
>>>
>>> http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libc/stdlib/getenv.c
>>
>> Follow-up: the manpages between 6.3-PRERELEASE and 7.0-STABLE do
>> document said change:
>>
>>
http://www.freebsd.org/cgi/man.cgi?query=getenv&apropos=0&sektion=3&manpath=FreeBSD+6.3-RELEASE&format=html
>
> Says that if the environment variable is NOT IN THE ENVIRONMENT then null 
> is returned.  Setting the variable to "" does put it in the
environment.
> env returns it properly.
>
>>
>>
>>
http://www.freebsd.org/cgi/man.cgi?query=getenv&apropos=0&sektion=3&manpath=FreeBSD+7.0-stable&format=html
>
> Same thing.  I find nothing documented about this change.
I'm not sure where you're going with this.  I see it clearly in the
ERRORS section.

But besides that, just like Bakul Shah, I cannot reproduce this problem:

$ uname -mr
7.0-STABLE amd64
$ gcc -o z z.c
$ ./z
getenv(FOO) = (null)
$ export FOO=yep
$ ./z
getenv(FOO) = yep
export FOO$ ./z
getenv(FOO) $ cat z.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char *e = getenv("FOO");

  printf("getenv(FOO) = %s\n", e);
  return 0;
}

Finally, why did you take freebsd-stable off this mail conversation?  If
others have the same question in the future, they're not going to be
able to read what partook here.  I'm re-adding the list.

-- 
| Jeremy Chadwick                                    jdc at parodius.com |
| Parodius Networking                           http://www.parodius.com/ |
| UNIX Systems Administrator                      Mountain View, CA, USA |
| Making life hard for others since 1977.                  PGP: 4BD6C0CB |