+
+ dnl Solaris 10 unsetenv does not remove all copies of a name.
+ dnl Haiku alpha 2 unsetenv gets confused by assignment to environ.
+ dnl OpenBSD 4.7 unsetenv("") does not fail.
+ AC_CACHE_CHECK([whether unsetenv obeys POSIX],
+ [gl_cv_func_unsetenv_works],
+ [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+ #include <stdlib.h>
+ #include <errno.h>
+ extern char **environ;
+ ]], [[
+ char entry1[] = "a=1";
+ char entry2[] = "b=2";
+ char *env[] = { entry1, entry2, NULL };
+ if (putenv ((char *) "a=1")) return 1;
+ if (putenv (entry2)) return 2;
+ entry2[0] = 'a';
+ unsetenv ("a");
+ if (getenv ("a")) return 3;
+ if (!unsetenv ("") || errno != EINVAL) return 4;
+ entry2[0] = 'b';
+ environ = env;
+ if (!getenv ("a")) return 5;
+ entry2[0] = 'a';
+ unsetenv ("a");
+ if (getenv ("a")) return 6;
+ ]])],
+ [gl_cv_func_unsetenv_works=yes], [gl_cv_func_unsetenv_works=no],
+ [case "$host_os" in
+ # Guess yes on glibc systems.
+ *-gnu*) gl_cv_func_unsetenv_works="guessing yes" ;;
+ # If we don't know, assume the worst.
+ *) gl_cv_func_unsetenv_works="guessing no" ;;
+ esac
+ ])])
+ case "$gl_cv_func_unsetenv_works" in
+ *yes) ;;
+ *)
+ REPLACE_UNSETENV=1
+ ;;
+ esac