$EUID

$ERRNO

$EGID

$EFFECTIVE_USER_ID

$EFFECTIVE_GROUP_ID

$DEBUGGING

$COMPILING

$CHILD_ERROR

$BASETIME

$b Special package variables when using sort(), see sort. Because of this specialness $a and $b don't need to be declared (using use vars , or our()) even when using the strict 'vars' pragma. Don't lexicalize them with my $a or my $b if you want to be able to use them in the sort() comparison block or function.