printenv: fix environ == NULL segfault

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/printenv.c

@@ -19,9 +19,14 @@ int printenv_main(int argc UNUSED_PARAM, char **argv)
 
 	/* no variables specified, show whole env */
 	if (!argv[1]) {
-		int e = 0;
-		while (environ[e])
-			puts(environ[e++]);
+		char **e = environ;
+
+		/* environ can be NULL! (for example, after clearenv())
+		 * Check for that:
+		 */
+		if (e)
+			while (*e)
+				puts(*e++);
 	} else {
 		/* search for specified variables and print them out if found */
 		char *arg, *env;