Psychologists are often faced with the need to manipulate one or more files, either to modify the format or to extract specific information. Traditionally, these manipulations have been performed using programming languages or statistical software, but such solutions are often expensive, platform dependent, or limited in their ability to handle both numerical and textual data. This tutorial introduces the perl programming language, a free, platform-independent language that excels at pattern matching and text processing but that is also numerically capable. A running example illustrates an application of perl to psychological data.