#!/bin/bash
uok2() {
    diff -U1000000000 "$1" "$2" | grep -v -e '^---' -e '^+++' -e ^'@@' | sed 's/^[ +-]//' | uniqo
}
in=`mktemp`
out=`mktemp`
for new; do
    uok2 "$in" "$new" >"$out"
    mv "$out" "$in"
done
cat "$in"
rm -f "$in" "$out"