The following options are recognised:

-i

Interactive. There is no string argument; instead look takes lines from the standard input as strings to be looked up.

-x

Exact. Print only lines of the file whose key matches string exactly.

-d

`Directory' order: only letters, digits, tabs and blanks participate in comparisons.

-f

Fold. Upper case letters compare equal to lower case.

-n

Numeric comparison with initial string of digits, optional minus sign, and optional decimal point.

-r endkey

Limit the range of matching values, to include the word endkey but no larger values.

-t[c]

Character c terminates the sort key in the file. By default, tab terminates the key. If c is missing the entire line comprises the key.

If no file is specified, /lib/words is assumed, with collating sequence df.