Word Frequency

Write a bash script to calculate the frequency of each word in a text file words.txt.

For simplicity sake, you may assume:

• words.txt contains only lowercase characters and space ' ' characters.
• Each word must consist of lowercase characters only.
• Words are separated by one or more whitespace characters.

For example, assume that words.txt has the following content:

the day is sunny the the
the sunny is is

Your script should output the following, sorted by descending frequency:

the 4
is 3
sunny 2
day 1

Note:
Don't worry about handling ties, it is guaranteed that each word's frequency count is unique.

1.这里只是把空格当成了分隔符，如果含有标点符号，还需要把标点符号考虑进去

2.注意sort对出现次数进行排序时需要指定参数-n，表示使用数值方式排序，默认是字符方式(“10”<"2")

cat words.txt | tr ' ' '
'|sort|sed '/^$/d'|awk '{a[$1]++}END{for(item in a)print item,a[item]}'|sort -k 2 -rn