The Perks of Being a Wallflower is a 2012 American coming-of-age drama film. An adaptation of the 1999 epistolary novel of the same name, it was written and directed by the novel's author, Stephen Chbosky. Filmed in Pittsburgh, Pennsylvania, the film was released on September 21, 2012, to positive critical response and commercial success, earning $33.4 million to a budget of $13 million. The film stars Logan Lerman, Emma Watson and Ezra Miller. Two or three years after the release of film, Chbosky began to speak more openly concerning the mental health care aspects of the film which were of significance to him in the original writing of the book and the production of the film as he conceived it. This is one of the three films from John Malkovich, Lianne Halfon and Russell Smith's Mr. Mudd Productions that feature struggling teenagers; the other two are Ghost World and Juno.

Based on this passage, who directed the perks of being a wallflower? Let's give stream of consciousness first:
The relevant information to answer the above question is: An adaptation of the 1999 epistolary novel of the same name, it was written and directed by the novel's author, Stephen Chbosky.
So, the final answer is Stephen Chbosky.