帶有鍵值對的for循環，鍵是不維護排序順序

我有下面的腳本，我注意到在這種情況下，for循環的執行順序不是我指定的，即。預計為 2018、2019、2020，但結果為 2019、2018、2020。

在 shell 腳本中是否有特定的原因，有什麼方法可以保留順序。

#!/bin/sh

declare -A arr
arr=( ["2018"]=5%12 ["2019"]=1%12 ["2020"]=1%2 )
INPUT_MONTH=$2
INPUT_YEAR=$1

#For loop to iterate the year(key) value of array
for year in ${!arr[@]}; do
 echo  ${year} ${arr[${year}]}
 MONTH_RANGE=${arr[${year}]}
 if [ ${year} -ge ${INPUT_YEAR} ]; then
   START_MONTH=$(echo "${MONTH_RANGE}" | cut -d'%' -f 1)
   END_MONTH=$(echo "${MONTH_RANGE}" | cut -d'%' -f 2)
   # input year is equal and input month is different from default start one.
   if [ "${year}" == "${INPUT_YEAR}" ]; then
     START_MONTH=$INPUT_MONTH
   fi
   for mon in $(seq $START_MONTH $END_MONTH); do
     echo "Process year:month <=> ${year}:${mon}"
   done;
 else
   continue;
 fi
done;

輸出：

2019 1%12
Process year:month <=> 2019:1
Process year:month <=> 2019:2
Process year:month <=> 2019:3
Process year:month <=> 2019:4
Process year:month <=> 2019:5
Process year:month <=> 2019:6
Process year:month <=> 2019:7
Process year:month <=> 2019:8
Process year:month <=> 2019:9
Process year:month <=> 2019:10
Process year:month <=> 2019:11
Process year:month <=> 2019:12
2018 5%12
Process year:month <=> 2018:4
Process year:month <=> 2018:5
Process year:month <=> 2018:6
Process year:month <=> 2018:7
Process year:month <=> 2018:8
Process year:month <=> 2018:9
Process year:month <=> 2018:10
Process year:month <=> 2018:11
Process year:month <=> 2018:12
2020 1%2
Process year:month <=> 2020:1
Process year:month <=> 2020:2

在 bash 中，declare -A arr聲明一個關聯數組。關聯數組中的鍵是散列的，並且${!arr[@]}不能保證1的遍歷順序。

$ declare -A arr
$ arr=( ["2018"]=5%12 ["2019"]=1%12 ["2020"]=1%2 )
$ for year in "${!arr[@]}"; do printf '%s: %s\n' "${year}" "${arr[${year}]}"; done
2019: 1%12
2018: 5%12
2020: 1%2

相反，declare -a arr聲明一個索引數組，它應該按您的預期排序：

$ declare -a arr
$ arr=( [2018]=5%12 [2019]=1%12 [2020]=1%2 )
$ for year in "${!arr[@]}"; do printf '%s: %s\n' "${year}" "${arr[${year}]}"; done
2018: 5%12
2019: 1%12
2020: 1%2

由於您的鍵（年）是數字，因此在這種情況下似乎沒有理由不使用索引數組。

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參考：

1. 如何保持關聯數組順序？

引用自：https://unix.stackexchange.com/questions/582347