more specifically how the switches work.
example from the manpage follows:
Same sort but sorting numerically on characters 3 through 5 of the fifth field first, and only return records with unique keys

sort_file({
        u => 1, r => 1, k => ['5.3,5.5rn', '2.2,2.2'],
        o => 'outfile', I => ['file1', 'file2']
    });
[download]

this example is really confusing, what is the 1 for in the u option? true?

Edit kudra, 2001-12-27 Replaced br with code