>perl -nle
"/(\w*)/; $i{$1}++; print qq{$. $_} for keys %i;" words2.txt
1 foo
2 bar
2 foo
3 bar
3 baz
3 foo
4 bar
4 baz
4 qux
4 foo
5 bar
5 baz
5 qux
5 foo
6 bar
6 baz
6 qux
6 foo
7 bar
7 baz
7 qux
7 foo
8 bar
8 baz
8 qux
8 foo
9 bar
9 baz
9 qux
9 foo