Linux shell - while 循环对外部变量的处理

用过linux shell里面的while循环的都知道，循环里面对外部变量的修改是不生效的。比如：

variable = old_value

cat file | while read line

do

     do something

     variable = new_value

done

echo $varable

=============================

输出将会是：old_value

解决办法：

variable = old_value

while read line

do

     do something

     variable = new_value

done < file

echo $variable

=============================

输出将会是：new_value