If any of the program options Mbdfhinr are given but no key fields are specified, sort compares the entire lines according to the global options. For the default case or the -m option, only output the first of a sequence of lines that compare equal. For the -c option, check that no pair of consecutive lines compares equal. Print only lines that are duplicates. Print only lines which have no duplicates.
Invalid names compare low to valid names.
Compare according to arithmetic value. Reverse the result of comparison, so that lines with greater key values appear earlier in the output instead of later. Several flags may be given. The flags affect only that column. In addition a specific subset of characters in a key column may be selected with the column range modifier.