prepend-copyright-header.txt

$ find . -name '*.[ch]pp' -exec sed -i -e '1r../header.txt' -e '1{h;d}' -e '2{x;G}' {} \;
$ find . -name '*.[ch]pp' -print | while read f; do sed -i 's/@file\(\s\+\)xxx/@file\1'$(basename $f)'/' "$f"; done
$ cat ../header.txt
// vim: set et wrap spell ts=2 sw=2 wm=80 tw=80 spelllang=en fenc=utf-8 cc=80:
/**
 * @file       xxx
 * @author     Krzysztof Ostrowski
 *
 * @copyright  Copyright (C) 2020 Krzysztof Ostrowski
 *
 * @license    All rights reserved.
 */