@if判断之while循环及for循环

文章目录

• ​​一 流程控制之if判断​​
• ​​二 流程控制之while循环​​
• ​​三 流程控制之for循环​​

一 流程控制之if判断

if 条件1;then

    代码1

    代码2

    .............

elif 条件2;then

    代码1

    代码2

...........

elif 条件3;then

    代码1

    代码2

.......

else

    代码1

    代码2

.........

fi      

案例1

#!/bin/bash

echo "start......"
read -p "请输入您的年龄: " age

if [ $age -eq 18 ];then
  echo "too young"
  echo "too young"
  echo "too young"
fi
echo "end......"      

案例2

#!/bin/bash

echo "start......"
read -p "请输入您的年龄: " age

if [ $age -eq 18 ];then
  echo "too young"
else
  echo "too old"
fi
echo "end......"      

案例3：

#!/bin/bash

read -p "请输入您的分数: " score

if [ $score -ge 90 ];then
    echo "优秀"
elif [ $score -ge 80 ] && [ $score -lt 90 ];then
    echo "良好"
elif [ $score -ge 70 ] && [ $score -lt 80 ];then
    echo "一般" 
else
    echo "很差"
fi      

案例4：

#!/bin/bash

read -p "请输入您的分数: " score

if [ $score -ge 90 ];then
    echo "优秀"
elif [ $score -ge 80 ];then
    echo "良好"
elif [ $score -ge 70 ];then
    echo "一般" 
else
    echo "很差"
fi      

案例5：

#!/bin/bash

read -p "输入用户名：" inp_user
read -p "输入密码：" inp_pwd

if [ $inp_user = "egon" ] && [ $inp_pwd = "123" ];then
  echo "登录成功"
else
  echo "用户名或者密码错误"
fi      

二 流程控制之while循环

1、什么是循环

2、为何要循环

3、如何用循环

#!/bin/bash

while true
do
  echo 111
  echo 222
  echo 333
done      

案例1

#!/bin/bash

while true
do
    read -p "输入用户名：" inp_user
    read -p "输入密码：" inp_pwd

    if [ $inp_user = "egon" ] && [ $inp_pwd = "123" ];then
        echo "登录成功"
    else
        echo "用户名或者密码错误"
    fi
done      

案例2：

#!/bin/bash

while true
do
    read -p "输入用户名：" inp_user
    read -p "输入密码：" inp_pwd

    if [ $inp_user = "egon" ] && [ $inp_pwd = "123" ];then
        echo "登录成功"
        break
    else
        echo "用户名或者密码错误"
    fi
done      

案例3：

# 多行
while 条件
do
  命令1
  命令2
  命令3
done

# 一行
while 条件;do 命令1;命令2;命令3; done

while true;do ifconfig eth0;sleep 0.5;clear; done      

三 流程控制之for循环

案例1

for i in {1..3}
do
    echo ok1 $i
    echo ok2 $i
    echo ok3 $i
done      

案例2

for x in "aaa" 2222 "ccc"
do
    echo $x
done      

案例3

#!/bin/bash

for i in {2..254}
do
    (
    ping -c1 1.1.1.$i &>/dev/null
    if [ $? -eq 0 ];then
        echo "1.1.1.$i
    else
        echo "1.1.1.$i
    fi
    ) &
done
#测试指定网段的所有ip的状态      

案例4：

#!/bin/bash

cd /root/test

for i in `ls`
do
mv $i `ls $i | cut -d "." -f1`.log

done 
#更改指定目录下的文件类型的后缀      

#！/bin/bash

while true
do
    read -p "(我)我牛逼:" who
    read -p "(你)我也牛逼:" you

    if [ $who = "yes" ] && [ $you = "yes" ];then
       echo "是真牛"
     elif [ $you = "no" ] || [ $who = "yes" ];then
       echo "不行啊"
       echo "你得低调"
       break
     else
       echo "再给你一次机会说"
    fi
done
#自我感觉良好的对话脚本