数组迭代

数组迭代有两种形式，foreach 和经典的 for 循环：

a=(1 2 3 4)
# foreach loop
for y in "${a[@]}"; do
    # act on $y
    echo "$y"
done
# classic for-loop
for ((idx=0; idx < ${#a[@]}; ++idx)); do
    # act on ${a[$idx]}
    echo "${a[$idx]}"
done

你还可以迭代命令的输出：

a=($(tr ',' ' ' <<<"a,b,c,d")) # tr can transform one character to another
for y in "${a[@]}"; do
    echo "$y"
done