$ grep -l "#piano" ~/blog/*

total 4

1. 2014-10-05 Piano Recital 2014-10 #piano
2. 2013-10-07 Piano Recital 2013-10 #piano
3. 2013-03-31 Piano Practice Session 1 #piano
4. 2013-01-29 What Every Pianist Needs to Know About the Body #books-magazines #piano