git filter-branch の使い方

http://git-scm.com/book/ja/v1/Git-%E3%81%AE%E3%81%95%E3%81%BE%E3%81%96%E3%81%BE%E3%81%AA%E3%83%84%E3%83%BC%E3%83%AB-%E6%AD%B4%E5%8F%B2%E3%81%AE%E6%9B%B8%E3%81%8D%E6%8F%9B%E3%81%88

git filter-branch --commit-filter '
        if [ "$GIT_AUTHOR_EMAIL" = "schacon@localhost" ];
        then
                GIT_AUTHOR_NAME="Scott Chacon";
                GIT_AUTHOR_EMAIL="schacon@example.com";
                git commit-tree "$@";
        else
                git commit-tree "$@";
        fi' HEAD