模拟数据。新建example.txt，写入以下文字：
If you often volunteer in a shelter (animal or human),you know how it feels to help those in need. You see many animals and people suffer from starvation,diseases,and loneliness. You see them die. Your heart is bleeding and you cannot stop crying,but you get up and keep helping the others. You stay emotionally strong and that strength is growing until you stop caring. Why are doctors so emotionally strong?
Finally,remember that life is jam-packed with ups and downs. The obstacles and problems are a part of your life. Can handle and solve them? Perfect. Can’t do it? It is totally normal. After all,you are just human. We learn a lot more useful things from failures and misfortunes than we do from success and happiness.
输入以下命令，出现结果：
cat example.txt | tr ' ' '\n' | sort | uniq -c
- cat example.txt 输出内容
- tr ' ' '\n' 将空格替换成换行符
- sort 排序(需要先进行排序,否则相同行中间的行会被忽略)
- uniq -c 去重并统计
