getenv semantics

Tony Maher anthony.maher at
Sat Oct 15 22:02:25 PDT 2005


I am trying to create a port of some 3rd party software and while
I can get it to compile ok and (mostly) run there are a few anomalies in
it detecting environment variables.  It appears to run ok on linux (I do
not have a convenient linux box for testing with).  I believe its the
way the code get the environment variables that is the cause. But if
thats the case then it would appear that getenv semantics differs 
slightly on different platforms.

     "When VARIABLE is not found or has no value, getenv() returns NULL."

But on FreeBSD it would appear that if VARIABLE is found but has no
value it returns a pointer to a NUL ('\0') string.

Is this analysis correct?  Can someone point me to the (a?) standard
that describes this.  The FreeBSD behaviour makes sense, I am trying to 
understand what is the expected behaviour on other platforms.


echo "unset foobar"
unset foobar

echo "export foobar"
export foobar

echo "export foobar=isset"
export foobar=isset

echo "unset foobar"
unset foobar


/* test-getenv.c */

#include <stdio.h>
#include <stdlib.h>

main(int argc, char *argv[])
   char *p;
   p = getenv("foobar");
   fprintf(stderr, "getenv('foobar') string is >%s< pointer is 
 >%x<\n",p, p);

unset foobar
getenv('foobar') string is >(null)< pointer is >0<
export foobar
getenv('foobar') string is >< pointer is >bfbfe933<
export foobar=isset
getenv('foobar') string is >isset< pointer is >bfbfe92f<
unset foobar
getenv('foobar') string is >(null)< pointer is >0<


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