To count by author: git log --numstat --no-merges --pretty=format:%an | awk ' au...

To count by author:

    git log --numstat --no-merges --pretty=format:%an
        | awk '
          author == "" { author = $0; next }
          /^$/ { author = ""; next }
          { added[author] += $1; removed[author] += $2 }
          END { for (author in added) {
            print author, "added", added[author], "removed", removed[author], "sum", added[author]-removed[author]
          } }'
        | sort -n -k 7