We have a set of directories containing lucene indexes. Each index is a mix of different file types (differentiated by extension) eg:

```
0/index/_2z6.frq
0/index/_2z6.fnm
..
1/index/_1sq.frq
1/index/_1sq.fnm
..
```

(it's about 10 different extensions)

We'd like to get a total by file extension, eg:

```
.frq 21234
.fnm 34757
..
```

I've tried various combinations of du/awk/xargs but finding it tricky to do exactly this.