Aaron Perrino and his band, The Sheila Divine, have been performing post-punk rock music in front of crowds since the late 1990s, but this year will mark the first time the four-member Boston-based group will step on the MayFair stage in Harvard Square. “It’s a pretty great line up this year,” said Perrino, 40, of Boston, who said he is going to bring his children to the festival. “I like playing in Harvard Square on Mass. Ave. It will be fun.”