今天刷Leecode（192 Word frequency）時，遇到一個shell語法問題，記錄下來。首先將題目描述和代碼呈上

#!/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:

# the4

# is3

# sunny2

# day1

# define a map

declare -A map=()

# iterator lines in file

L24 #cat words.txt |whileread line

whileread line

do

forword in $line

do

? ? ? ? echo $word

if[ -z ${map[$word]} ];then

map[$word]=1

else

? ? ? ? ? ? let map[$word]++

? ? ? ? fi?

? ? done

L36done < words.txt

forkey in ${!map[@]}

do

? ? echo $key ${map[$key]}

done

題目的意思是統(tǒng)計一個文件中單詞重復的次數(shù)，開始寫法如L24，while循環(huán)結(jié)束后，map依然為空，后來才知道是使用了管道的緣故

當啟用管道時，會生成一個subshell，while循環(huán)的代碼在subshell中執(zhí)行，那么變量map也是在subshell中被修改，

while循環(huán)結(jié)束后，回到主shell，map沒有被修改，也就是說，兩個map不是同一個map，while中修改的map是外層map的副本

修改代碼，將讀取文件的格式改成L36，程序運行正常