case与循环

case语法

case "var" in 
    value1 )
        command_block1
        ;;
    value2 )
        command_block2
        ;;
    * )
        command_block3
esac

示例

read -p "please input a number in [0-9]>" num
case $num in 
    1)
            echo "you typed 1!"
        ;;
    2)
        echo "you typed 3!"
        ;;
    [3-9])
        echo "you typed $num"
        ;;
    *)
        echo "invalid augument!"
esac

while循环
语法格式

while condition
do
    command_block
done

until condition
do 
    command_block
done

while会在条件成立时进入循环体，直到条件不成立退出，until会在条件不成立时进入循环体，直到条件成立退出
while循环按行读取文件

exec <test.sh
while read line
do
    echo $line
done

cat test.sh | while read line
do
        echo $line
done

for循环与select,select用于菜单选项执行,循环过程中取值列表可省略，表示$@

for var in (val1 val2 val3)
do 
    command_block
done

for((exp1;exp2;exp3))
do
    command_block
done

select var in [ var list ]
do
    command_block
done

select示例（PS3代表命令提示符，$REPLY代表选择的数字)

PS3="select a num for menu>"
select name in xiaoming xiaohong xiaobai
do
    echo "you selected : $REPLY)$name"
done    

continue、break、return、exit对比其他语言理解