参看下面的代码，想问一下Carol Echols中的Echols为什么匹配对应的last变量？([^\s]+\s+)这个匹配到底表示的是啥意思……求高人解答，谢谢！


data old;
   input name $60.;
   datalines;
Judith S Reaveley
Ralph F. Morgan
Jess Ennis
Carol Echols
Kelly Hansen Huff
Judith
Nick
Jones
;

data new;
   length first middle last $ 40;
   re1 = prxparse('/(\S+)\s+([^\s]+\s+)?(\S+)/o');
   re2 = prxparse('/(\S+)(\s+)([^\s]+\s+)(?)(\S+)/o');
   set old;
   id1=prxmatch(re1, name);
   id2=prxmatch(re2, name);
   if id1 then
      do;
         first = prxposn(re1, 1, name);
         middle = prxposn(re1, 2, name);
         last = prxposn(re1, 3, name);
      end;
   if id2 then test=prxposn(re1, 4, name);
   put test=;
run;