In a PDF found here, "Lightweight Database Techniques" tutorial materials freed, Dominus says Tie::File is for convenience, not performance, but he also says its reasonably fast. The job you're doing here is removing the first 4 lines of every (200,000) files. Tie::File will have to rewrite every large file from the point beyond the change to the end. He says since the module must perform reasonable well for many different types of applications, its slower than code custom written for a single application.