As the fall television season begins, and new and returning shows jostle one another to remind easily distracted viewers that they exist, there are many routes series can take to promote themselves. Some buy print advertisements and rent billboards; others use Internet banners and viral videos. But probably only one is sending its cast on the road to perform a live musical.

For the past several days the stars of the irreverent FX comedy “It’s Always Sunny in Philadelphia” (whose fifth season begins on Thursday, by the way) have been readying for a six-city tour. They will act, sing and karate-kick their way through “The Nightman Cometh,” an original stage work taken from a recent episode of the show. Costumes and sets have been packed up, a tour bus has been prepared, and a few days ago some (but not all) of the cast members even got together to rehearse for, like, four hours.

Asked recently if he had the musical-theater background to pull this off, Rob McElhenney, the show’s creator and co-star, gave a long, nervous laugh.

“No,” he said. “No. No, I don’t. I don’t really have any comedy background. This show is the first comedy I’ve done. Now we’re doing it in front of 4,000 people at a clip. It’s going to be pretty interesting.”