--- a/src/core/object-base.cc	Tue Feb 24 10:26:57 2009 +0100
+++ b/src/core/object-base.cc	Tue Feb 24 10:27:08 2009 +0100
@@ -22,6 +22,10 @@
 #include "trace-source-accessor.h"
 #include "attribute-list.h"
 #include "string.h"
+#include "ns3/core-config.h"
+#ifdef HAVE_STDLIB_H
+#include <stdlib.h>
+#endif
 
 NS_LOG_COMPONENT_DEFINE ("ObjectBase");
 
@@ -76,25 +80,10 @@
             if (j->checker == checker)
               {
                 // We have a matching attribute value.
-                DoSet (accessor, checker, *j->value);
-                NS_LOG_DEBUG ("construct \""<< tid.GetName ()<<"::"<<
-                              tid.GetAttributeName (i)<<"\"");
-                found = true;
-                break;
-              }
-          }
-        if (!found)
-          {
-            // is this attribute stored in the global instance instance ?
-            for (AttributeList::Attrs::const_iterator j = AttributeList::GetGlobal ()->m_attributes.begin ();
-                 j != AttributeList::GetGlobal ()->m_attributes.end (); j++)
-              {
-                if (j->checker == checker)
+                if (DoSet (accessor, checker, *j->value))
                   {
-                    // We have a matching attribute value.
-                    DoSet (accessor, checker, *j->value);
                     NS_LOG_DEBUG ("construct \""<< tid.GetName ()<<"::"<<
-                                  tid.GetAttributeName (i)<<"\" from global");
+                                  tid.GetAttributeName (i)<<"\"");
                     found = true;
                     break;
                   }
@@ -102,7 +91,61 @@
           }
         if (!found)
           {
-            // No matching attribute value so we set the default value.
+            // is this attribute stored in the global instance ?
+            for (AttributeList::Attrs::const_iterator j = AttributeList::GetGlobal ()->m_attributes.begin ();
+                 j != AttributeList::GetGlobal ()->m_attributes.end (); j++)
+              {
+                if (j->checker == checker)
+                  {
+                    // We have a matching attribute value.
+                    if (DoSet (accessor, checker, *j->value))
+                      {
+                        NS_LOG_DEBUG ("construct \""<< tid.GetName ()<<"::"<<
+                                      tid.GetAttributeName (i)<<"\" from global");
+                        found = true;
+                        break;
+                      }
+                  }
+              }
+          }
+        if (!found)
+          {
+            // No matching attribute value so we try to look at the env var.
+#ifdef HAVE_GETENV
+            char *envVar = getenv ("NS_ATTRIBUTE_DEFAULT");
+            if (envVar != 0)
+              {
+                std::string env = std::string (envVar);
+                std::string::size_type cur = 0;
+                std::string::size_type next = 0;
+                while (next != std::string::npos)
+                  {
+                    next = env.find (";", cur);
+                    std::string tmp = std::string (env, cur, next-cur);
+                    std::string::size_type equal = tmp.find ("=");
+                    if (equal != std::string::npos)
+                      {
+                        std::string name = tmp.substr (0, equal);
+                        std::string value = tmp.substr (equal+1, tmp.size () - equal - 1);
+                        if (name == tid.GetAttributeFullName (i))
+                          {
+                            if (DoSet (accessor, checker, StringValue (value)))
+                              {
+                                NS_LOG_DEBUG ("construct \""<< tid.GetName ()<<"::"<<
+                                              tid.GetAttributeName (i)<<"\" from env var");
+                                found = true;
+                                break;
+                              }
+                          }
+                      }
+                    cur = next + 1;
+                  }
+              }
+#endif /* HAVE_GETENV */
+          }
+        if (!found)
+          {
+            // No matching attribute value so we try to set the default value.
             DoSet (accessor, checker, *initial);
             NS_LOG_DEBUG ("construct \""<< tid.GetName ()<<"::"<<
                           tid.GetAttributeName (i)<<"\" from initial value.");