Emmylou Harris, Patty Griffin, Shawn Colvin and Buddy Miller

Four folk and country icons team up for what promises to be a very informal collaborative concert at the Pabst Theater. Three of the four—folkie Patty Griffin, country traditionalist Buddy Miller and country legend/alt-country queen Emmylou Harris—launched a similar tour in 2004 called the “Sweet Harmony Traveling Revue,” but this one, “Three Girls and their Buddy,” swaps Gillian Welch and David Rawlings for Shawn Colvin, the folk-rocker who scored a major hit in the late-’90s with her revenge tale, “Sunny Came Home.”