bash和sh shell脚本中的变量范围

Question

有关Bourne Shell语言和Bourne Again Shell语言中变量范围的问题。两者具有相同的行为。

#!/bin/sh

CHANGE_MADE="0"

printf "1\n2\n3\n " | while read NUMBER
do
  if [ "$NUMBER" = "2" ]
  then
    CHANGE_MADE="1"
    echo "In condition CHANGE_MADE= $CHANGE_MADE"
  fi

  echo "In loop CHANGE_MADE= $CHANGE_MADE"
done

echo "Out of loop: CHANGE_MADE= $CHANGE_MADE"

实际结果：

:~$ Public_cleaner.sh 
In loop CHANGE_MADE= 0
In condition CHANGE_MADE= 1
In loop CHANGE_MADE= 1
In loop CHANGE_MADE= 1
Out of loop: CHANGE_MADE= 0
:~$ 

我曾期望在最后一行CHANGE_MADE为1。为什么它为零？