'PrintTo' prints all following arguments to the file with the name 'filename'. It opens the file with the name 'filename'. If the file does not exist it is created, otherwise it is truncated. If you do not want to truncate the file use 'AppendTo'. After opening the file 'PrintTo' evaluates its arguments in turn and prints the values to 'filename'. Finally it closes the file again. During evaluation of the arguments 'filename' is the current output file. This means that output printed with 'Print' during the evaluation, for example to inform the user about the progress, also goes to 'filename'. To make this feature more useful 'PrintTo' will silently ignore if one of the arguments is a procedure call, i.e., does not return a value.