Perl Regex ： ？＝

见： Pleac Perl - Pattern Matching

$digits = "123456789";
@nonlap = $digits =~ /(\d\d\d)/g;
@yeslap = $digits =~ /(?=(\d\d\d))/g;
print "Non-overlapping:  @nonlap\n";
print "Overlapping:      @yeslap\n";

# Non-overlapping:  123 456 789
# Overlapping:      123 234 345 456 567 678 789