Words may be quoted with the characters (") (double quote), and (') (single quote). A word enclosed by either of these quotes may contain white space. A string enclosed by double quotes may have further special-character substitutions done on it, but it will be considered a single token by the shell. A number so quoted is considered a string. A string enclosed by single quotes also has all its special characters protected. Thus no global expansion (*, ?, etc), variable expansion ($), or history substitution (^, !) will be done.