今天刷Leecode（192 Word frequency）时，遇到一个shell语法问题，记录下来。首先将题目描述和代码呈上
-
#!/bin/bash -
# 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 -
# define a map -
declare -A map=() -
# iterator lines in file -
#cat words.txt | while read line -
while read line -
do -
for word in $line -
do -
echo $word -
if [ -z ${map[$word]} ];then -
map[$word]=1 -
else -
let map[$word]++ -
fi -
done -
done < words.txt -
for key in ${!map[@]} -
do -
echo $key ${map[$key]} -
done
题目的意思是统计一个文件中单词重复的次数，开始写法如L24，while循环结束后，map依然为空，后来才知道是使用了管道的缘故
当启用管道时，会生成一个subshell，while循环的代码在subshell中执行，那么变量map也是在subshell中被修改，
while循环结束后，回到主shell，map没有被修改，也就是说，两个map不是同一个map，while中修改的map是外层map的副本
修改代码，将读取文件的格式改成L36，程序运行正常