# 6. 流程控制

## if-else

```bash
if condition
then
    command1
    command3
    command2
fi
```

```bash
if condition
then 
    command1
    ...
else

    commad1
    ...
fi
```

## if-else-if

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

## for 循环

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

## while 循环

```bash
while condition
do
    command
done
```

## until 循环

```bash
until condition
do
    command
done
```

## case 多分支选择

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

demo

```bash
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


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