Filter commands accept input from the default device, manipulate the data in some
fashion, and send the results to the default output device. A commonly used filter is
SORT, which accepts input from the keyboard, sorts that data, and displays it on the
screen. This filter command becomes even more useful if it can read data from a file
and sort it to another file. This can be done by using the redirectional parameters. For
example, if you wanted to sort a data file called STD.DAT and store it in another file
called SORTSTD.DAT, then you’d type: