diff --git a/bin/purge b/bin/purge
new file mode 100755
index 0000000..2fc4033
--- /dev/null
+++ b/bin/purge
@@ -0,0 +1,12 @@
+#!/bin/sh
+if [ "$1" ]; then
+    cd "$1" || exit
+fi
+git ls-files -m | grep '.pro$' |
+    while read n; do
+	if ! [ "`git diff "$n" |
+	  sed '/^--- /d;/^+++ /d;/^[^-+]/d;/^.update=/d'`" ]; then
+	    echo purging "$n" 1>&2
+	    git checkout "$n"
+	fi
+    done