1. 我的答案，很啰嗦

      1. cat words.txt | 
      2. tr ' ' '\n' | 
      3. sort | 
      4. awk 'BEGIN{last="";count=0;}{if(last==""){last=$0;count=0;} if(last==$0){count++;}else{printf "%s %s\n", last, count; last=$0;count=1;} }END{printf "%s %s\n", last, count}' | sort -k 2,2nr

    2. 正确的答案

      cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -r | awk '{print $2,$1}'

    忘记了 uniq -c 可以统计重复元素的数量