@@ -21,20 +21,22 @@
 (declare (unit env))
 
 (use sql-de-lite) ;; srfi-1 posix regex regex-case srfi-69 srfi-18 call-with-environment-variables)
 
 (define (env:open-db fname)
-  (let* ((db-exists (common:file-exists? fname))
+  (let* ((db-exists (if (equal? fname ":memory:")
+			#f
+			(common:file-exists? fname)))
 	 (db        (open-database fname)))
     (if (not db-exists)
 	(begin
-	  (exec (sql db "CREATE TABLE envvars (
-                    id INTEGER PRIMARY KEY,
-                    context TEXT NOT NULL,
-                    var TEXT NOT NULL,
-                    val TEXT NOT NULL,
-                       CONSTRAINT envvars_constraint UNIQUE (context,var))"))))
+	  (exec (sql db "CREATE TABLE IF NOT EXISTS envvars (
+                            id INTEGER PRIMARY KEY,
+                            context TEXT NOT NULL,
+                            var TEXT NOT NULL,
+                            val TEXT NOT NULL,
+                               CONSTRAINT envvars_constraint UNIQUE (context,var))"))))
     (set-busy-handler! db (busy-timeout 10000))
     db))
 
 ;; save vars in given context, this is NOT incremental by default
 ;;
@@ -77,10 +79,33 @@
 				  val)))))
 	(sql db "SELECT var,val FROM envvars WHERE context=?")
 	context))
      contexts)
     result))
+
+;; envdelta: a-b (start=a, end=b, get the delta)
+;; ofile:    #f = write to stdout, else write to file with string name
+;;
+(define (env:envdelta db envdelta ofile)
+  (let ((match (string-split envdelta "-")));; (string-match "([a-z0-9_]+)=([a-z0-9_\\-,]+)" envdelta)))
+    (if (not (null? match))
+	(let* ((parts     match) ;; (string-split equn "-"))
+	       (minuend   (car parts))
+	       (subtraend (cadr parts))
+	       (added     (env:get-added   db minuend subtraend))
+	       (removed   (env:get-removed db minuend subtraend))
+	       (changed   (env:get-changed db minuend subtraend)))
+	  ;; (pp (hash-table->alist added))
+	  ;; (pp (hash-table->alist removed))
+	  ;; (pp (hash-table->alist changed))
+	  (if (args:get-arg "-o")
+	      (with-output-to-file
+		  (args:get-arg "-o")
+		(lambda ()
+		  (env:print added removed changed)))
+	      (env:print added removed changed)))
+	#f)))
 
 ;;  get list of removed variables between two contexts
 ;;
 (define (env:get-removed db contexta contextb)
   (let ((result (make-hash-table)))