1. The two or three characters which control history expansion and tokenization (see HISTORY EXPANSION below). The first character is the history expansion character, that is, the character which signals the start of a history expansion, normally `!'. The second character is the quick substitution character, which is used as shorthand for re-running the previous command entered, substituting one string for another in the command. The default is `^'. The optional third character is the character which signifies that the remainder of the line is a comment, when found as the first character of a word, normally `#'. The history comment character causes history substitution to be skipped for the remaining words on the line. It does not necessarily cause the shell parser to treat the rest of the line as a comment. From Rute-Users-Guide