--- a/lib/pvl/apply/cmd.sh	Sun Mar 01 23:16:18 2015 +0200
+++ b/lib/pvl/apply/cmd.sh	Sun Mar 01 23:32:32 2015 +0200
@@ -12,7 +12,7 @@
     cmd "${@:2}" > "$tmp"
 
     # compare
-    if [ -e "$out" -a -z "$APPLY_DIFF" ]; then
+    if [ -e "$out" -a -n "$APPLY_DIFF" ]; then
         debug "  changes:"
 
         # terse