6. 流程控制

if-else

if condition
then
    command1
    command3
    command2
fi

if condition
then 
    command1
    ...
else

    commad1
    ...
fi

if-else-if

if condition
then
    command1
    commadn2
    ...
elif condition
then
    commadm
    ..
else
    ...
fi

for 循环

for varname in item1 item2 ... itemN
do
    command1
    command2
    ...
    commandN
done

while 循环

while condition
do
    command
done

until 循环

until condition
do
    command
done

case 多分支选择

case value in
p1) 
    command1
    command2
    ;;
p2)
    command1
    command2
    ;;
esac

demo

echo '输入 1 到 4 之间的数字:'
echo '你输入的数字为:'
read aNum
case $aNum in
    1)  echo '你选择了 1'
    ;;
    2)  echo '你选择了 2'
    ;;
    3)  echo '你选择了 3'
    ;;
    4)  echo '你选择了 4'
    ;;
    *)  echo '你没有输入 1 到 4 之间的数字'
    ;;
esac

break

跳出后续所有的循环

continue

跳出当前循环