Set to 1 to do multi-line matching within a string, 0 to tell Perl that it can assume that strings contain a single line, for the purpose of optimizing pattern matches. Pattern matches on strings containing multiple newlines can produce confusing results when "$*" is 0. Default is 0. (Mnemonic: * matches multiple things.) Note that this variable influences the interpretation of only "^" and "$". A literal newline can be searched for even when $* == 0.
Use of "$*" is deprecated in modern Perls, supplanted by the /s and /m modifiers on pattern matching.