如何在bash中使用全局數組？

Question

我在SO和google中搜索了2天的解決方案，但是我沒有運氣。 我的問題是我有一個數組，並用0初始化了它的元素，並且在for \\ while循環范圍內修改了它的元素值。 但是當我在循環外打印數組的值時，我發現所有的0都是它們的初始值！

這是我的代碼：

#!/bin/bash
#
# This is a script to reformat CSV files into pretty-formatted txt files.

clear

echo 'This is a script to reformat CSV files into pretty-formatted txt files.'
echo

# Get number of elements.
elements=$(cat CSV_File | sed -n 1'p' | tr ',' '\n' | wc -l)
# "cat CSV_File" for getting text of the file.
# "sed -n 1'p'" for getting only first line.
# "tr ',' '\n'" for replacing ',' with '\n'.
# "wc -l" for getting number of lines (i.e number of elements).

# Get number of lines.
lines=$(cat CSV_File | wc -l)
# "cat CSV_File" for getting text of the file.
# "wc -l" for getting number of lines.

# Initiate an array for elements' lengths.
for ((i=1; $i < (( $elements + 1 )) ;i++))
do lengths[$i]="0"
done

# Find tallest element of each column and put the values into 'lengths' array.
for ((i=1; $i <= $lines ;i++))
do
   j="1"
   cat CSV_File | sed -n ${i}'p' | tr ',' '\n' | while read element
   do
      if [ ${lengths[$j]} -le ${#element} ]
      then lengths[$j]=${#element}
      fi
      (( j++ ))
   done
done

echo ${lengths[1]} # It should print 5 not 0
echo ${lengths[2]} # It should print 4 not 0
echo ${lengths[3]} # It should print 19 not 0
echo ${lengths[4]} # It should print 11 not 0
echo ${lengths[5]} # It should print 2 not 0
echo ${lengths[6]} # It should print 5 not 0
echo ${lengths[7]} # It should print 14 not 0
echo

...

這是CSV_File的內容：

Jones,Bill,235 S. Williams St.,Denver,CO,80221,(303) 244-7989
Smith,Tom,404 Polk Ave.,Los Angeles,CA,90003,(213) 879-5612

請注意，當我將echo放入if語句中時，它將輸出正確的值：

if [ ${lengths[$j]} -le ${#element} ]
then lengths[$j]=${#element}
     echo ${lengths[$j]}
fi

我在做什么錯？ 我想念什么嗎？

Answer 1

| while read element; do ... done | while read element; do ... done | while read element; do ... done在子外殼| while read element; do ... done中運行，因此在子外殼程序退出時，其對全局的更新會丟失。

一種解決方案是使用bash的“進程替換”來獲取while循環的輸入，以使其在子shell中運行。 請參閱： 在bash中讀取多行而不產生新的subshel​​l？