Looks through a sorted file and prints all lines that begin with
string. Words may be up to 256 characters long. This program is potentially faster than fgrep because it relies on the
file being sorted already, and can thus do a binary search through the file, instead of reading it sequentially from beginning to end.
file, look searches /usr/share/dict/words(the spelling dictionary) with options -df. This can be a handy way to look up a word in the dictionary if you only know the start of the word. If you can't remember how to spell "carburetor," try look carbur to see the 12 words in the dictionary that start "carbur."
Use dictionary order. Only letters, digits, spaces, and tabs are used in comparisons.
Fold case; ignore case distinctions in comparisons.
char as the termination character, i.e., ignore all characters to the right of