$* $* was a variable that you could use to enable multiline matching. After a deprecation

$SUBSEP

${^POSTMATCH} This is similar to $' ($POSTMATCH

$PERLDB

$<digits> ($1, $2, ...) Contains the subpattern from the corresponding set of capturing parentheses from the last successful pattern

$< The real uid of this process. You can change both the real uid and the effective uid at the same time by using

$( The real gid of this process. If you are on a machine that supports membership in multiple groups simultaneously, gives a space separated

${^GLOBAL_PHASE} The current phase of the perl interpreter. Possible values are:

NAME

NAME