| -c | Precede each output line with the count of the number of times the line occurred in the input, followed by a single space. |
| -d | Only output lines that are repeated in the input. |
| -f num | Ignore the first num fields in each input line when doing comparisons. A field is a string of non-blank characters separated from adjacent fields by blanks. Field numbers are one based, i.e., the first field is field one. |
| -s chars |
| | Ignore the first chars characters in each input line when doing comparisons. If specified in conjunction with the -f option, the first chars characters after the first num fields will be ignored. Character numbers are one based, i.e., the first character is character one. |
| -u | Only output lines that are not repeated in the input. |
| -i | Case insensitive comparison of lines. |
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