Cook is a tool for constructing files. It is given a set of files to create, and recipes of how to create them. In any non-trivial program there will be prerequisites to performing the actions necessary to creating any file, such as include files. Cook provides a mechanism to define these. When a program is being developed or maintained, the programmer will typically change one file of several which comprise the program. Cook examines the last-modified times of the files to see when the prerequisites of a file have changed, implying that the file needs to be recreated as it is logically out of date. Cook also provides a facility for implicit recipes, allowing users to specify how to form a file with a given suffix from a file with a different suffix. For example, to create filename.o from filename.c