--- mongodb-src-r1.3.5/db/update.cpp	2010-03-22 22:12:51.000000000 -0400
+++ mongodb-src-replace/db/update.cpp	2010-03-25 13:35:58.000000000 -0400
@@ -30,7 +30,7 @@
 #define DEBUGUPDATE(x)
     
     const char* Mod::modNames[] = { "$inc", "$set", "$push", "$pushAll", "$pull", "$pullAll" , "$pop", "$unset" ,
-                                    "$bitand" , "$bitor" , "$bit" , "$addToSet" };
+                                    "$bitand" , "$bitor" , "$bit" , "$addToSet", "$replace" };
     unsigned Mod::modNamesNum = sizeof(Mod::modNames)/sizeof(char*);
 
     bool Mod::_pullElementMatch( BSONElement& toMatch ) const {
@@ -298,6 +298,26 @@
             break;
         }
 
+        case REPLACE: {
+            string str(in.valuestrsafe());
+            BSONObj values = elt.embeddedObject();
+            BSONElement searchElem = values[0];
+            BSONElement replaceElem = values[1];
+            const char *search = searchElem.valuestrsafe();
+            int searchSize = searchElem.valuestrsize() - 1; 
+            const char *replace = replaceElem.valuestrsafe();
+            int replaceSize = replaceElem.valuestrsize() - 1;
+            string::size_type pos = 0;
+
+            while ( (pos = str.find(search, pos)) != string::npos ) {
+                str.replace( pos, searchSize, replace );
+                pos += replaceSize;
+            }
+
+            b.append( shortFieldName, str );
+            break;
+        }
+
         default:
             stringstream ss;
             ss << "Mod::apply can't handle type: " << op;
diff -ur mongodb-src-r1.3.5/db/update.h mongodb-src-replace/db/update.h
--- mongodb-src-r1.3.5/db/update.h	2010-03-22 22:12:51.000000000 -0400
+++ mongodb-src-replace/db/update.h	2010-03-25 13:36:27.000000000 -0400
@@ -32,8 +32,8 @@
      */
     struct Mod {
         // See opFromStr below
-        //        0    1    2     3         4     5          6    7      8       9       10    11
-        enum Op { INC, SET, PUSH, PUSH_ALL, PULL, PULL_ALL , POP, UNSET, BITAND, BITOR , BIT , ADDTOSET  } op;
+        //        0    1    2     3         4     5          6    7      8       9       10    11        12
+        enum Op { INC, SET, PUSH, PUSH_ALL, PULL, PULL_ALL , POP, UNSET, BITAND, BITOR , BIT , ADDTOSET, REPLACE  } op;
         
         static const char* modNames[];
         static unsigned modNamesNum;
@@ -251,6 +251,11 @@
                     
                 }
             }
+            case 'r': {
+                if ( fn[2] == 'e' && fn[3] == 'p' && fn[4] == 'l' && fn[5] == 'a' && fn[6] == 'c' && fn[7] == 'e' && fn[8] == 0 )
+                    return Mod::REPLACE;
+                break;
+            }
             default: break;
             }
             uassert( 10161 ,  "Invalid modifier specified " + string( fn ), false );