/usr/bin/look [-d] [-f] [-tc] string [filename]
The look command consults a sorted filename and prints all lines that begin with string.
If no filename is specified, look uses /usr/share/lib/dict/words with collating sequence –df.
look limits the length of a word to search for to 256 characters.
Dictionary order. Only letters, digits, TAB and SPACE characters are used in comparisons.
Fold case. Upper case letters are not distinguished from lower case in comparisons.
Set termination character. All characters to the right of c in string are ignored.
See attributes(5) for descriptions of the following attributes: