shell脚本中的语句

###语句########
学习目标：
for 语句
while语句
if语句
case语句
expect语句
exit,break,continue
{1…10}
seq 1 10
都是1-10








eg:

10秒倒计时：
#!/bin/bash
for SEC in {10..1}
do
  echo -n "After ${SEC}s is end "  ##-n表示不换行输出
 echo -ne "\r"  ##后面的信息把前面的刷掉
 sleep 1  ##1秒执行一次
done

eg:20台主机 1-20中开着的主机  找出来导入host_ip
>>不会覆盖之前的数据

#!/bin/bash
[ -e "/mnt/host_ip" ]&&{
    echo /mnt/host_ip is exist!!!
    echo "[O]verwrite [B]ackup [S]kip"
    read -p "What do you want action: " WORD
    ACTION=`echo $WORD|tr 'a-z' 'A-Z'`
    [ "$ACTION" = "O" ]&&{
            rm -fr /mnt/host_ip
    }
    [ "$ACTION" = "B" ]&&{
            mv /mnt/host_ip /mnt/host_ip.bak
    }
    [ "$ACTION" = "S" ]&&{
            exit 0
    }

}
for ip in {1..20}
do
    ping -c1 -w1 172.25.254.$ip &>/dev/null &&{
            echo 172.25.254.$ip >> /mnt/host_ip
}
done

######while##############
相当于&& 只不过可以循环
until 相当于||
while语句
while条件
do
done

eg:每隔1秒自减

1分10秒倒计时
1:00 --- 0:59

SEC=10
MIN=2
for ((SEC=10;SEC>=0;SEC--))
do
    while [ "$SEC" = "0" -a "$MIN" = "0" ]
    do
            exit 0
    done

    while [ "$SEC" = "0" ]
    do
             echo -ne "After $MIN:$SEC is end!!!!!!"
             echo -ne "\r"
             sleep 1     ##如果不执行这个不会出现 $MIN:0
             SEC=59  ##如果不加这个在SEC执行到0的时候会卡住，需要重新赋值。
            ((MIN--))

    done
    echo -ne "After $MIN:$SEC is end!!"
    echo -ne "\r"
    sleep 1
done

执行到0:00退出

######### if语句

if 效率低
从上往下执行
if
then
elif
then
。。。
else
fi ##语句结束

简单的示例:‘

【1】只有if，then，fi
vim test.sh 

if [  -z "$1" ]
then
    echo -e "\033[31mPlease input filename following $0!!!\033[0m"
    exit 1
fi

【2】只有if，then，elif，fi

vim  test.sh 
#!/bin/bash
if [  -z "$1" ]
then
    echo -e "\033[31mPlease input filename following $0!!!\033[0m"
    exit 1
elif [ -e "$1" ]
then
    echo "$1 is exist"
    exit 0
fi



sh test.sh
sh test.sh westos

【3】加入else

 vim test.sh 
	if [  -z "$1" ]
then
    echo -e "\033[31mPlease input filename following $0!!!\033[0m"
    exit 1
elif [ -e "$1" ]
then
    echo "$1 is exist"
    exit 0
else            ##除了以上情况外，输入以下内容
    echo "$1 is directory"
fi



sh test.sh
sh test.sh westos 
sh test.sh hello

继续提示Please input filename：exit(大小写都退出) 不用tr 因为下面还要判断这个真实文件

练习1：

判断

[root@localhost mnt]# checkfiletype.sh \
> Please input filename: /mnt \
> /mnt is directory \
> /mnt is not exist \
> Please input filename: exit \
> bye
步骤：
vim checkfiletype.sh
 #!/bin/bash
while true
do
    read -p "Please input filename [or exit or quit]: " NAME
    if [ "$NAME" = "EXIT " -o "$NAME" = "exit" ]
    then
            echo bye~~~
            exit 0
    elif [ -L "$NAME" ]
    then
            echo "$NAME is softlink file"
    elif [ -d "$NAME" ]
    then
        echo "$NAME is directory!"
    elif [ -f "$NAME" ]
    then
            echo "$NAME is common file"
    else
            echo "$NAME is not exist!!!"
    fi
done
sh checkfiletype.sh

练习2：

当执行filectrl -a file ##创建文件
-d 删掉
-p 备份到/mnt目录下
什么都不是，则报错

#!/bin/bash
Check_File()    【1】
{
    if [ -e "$1" ]
    then
            $2     ##相当于"echo $2 is exist !" 
            $3     ##相当于exit
    fi 
}
if [ "$#" -lt "2" ]
then
    echo -e  "\033[31mError:Please input option [-a|-d|-p] and following filename $0:\033[0m"
    exit 1
fi

if [ "$1" = "-a" ]
then
    Check_File $2 "echo $2 is exist !" exit
    touch $2
elif [ "$1" = "-d" ]
then
    Check_File $2 "rm -fr $2" exit
    echo "$2 is not exist"
elif [ "$1" = "-p" ]
then
     Check_File $2 "cp -rp $2 /mnt" exit
     echo "$2 is not exist"
else
     echo "Please input option [-a|-d|-p] following $0!!"
fi

测试：
  sh /mnt/filectrl.sh -a file
  sh /mnt/filectrl.sh -d file
  sh /mnt/filectrl.sh -p /etc/passwd
  ls  /mnt

第一种：


第二种：（使用函数）

############### case ,点名机制，速度快，做整体对比，进行匹配
case ##代替if,比较方便

esca
易懂的示例：

vim case.sh

#!/bin/bash
case $1 in
    westos)
    echo linux
    ;;
    linux)
    echo redhat
    ;;
    redhat)
    echo westos
    ;;
    *)    ###输入其他，显示错误
    echo Error
esac


sh case.sh westos
sh case.sh linux
sh case.sh redhat
sh case.sh haha

##练习3：在练习2 的基础上修改