if 语法
[]两边都有空格
if [ 表达式 ];then 执行的命令 fi if [ 如果你有房子 ];then 我就嫁给你 fi if第二种书写方式 if [ 表达式 ] then 执行的命令 fi
if 单分支
if [ -f /etc/passwd ] then echo ok fi if [ 10 -eq 10 ] then echo ok fi if [ "root" =~ ^r ] then echo ok fi
if 双分支结构
if [ 10 -eq 10 ] then echo 成立 else echo 不成立 fi
多分支结构 多个条件
if [ $1 -lt 20 ] then echo 小了 elif [ $1 -gt 20 ] echo 大了 else echo 相等 fi
案例1: 输入两个数字 使用if判断来比较两个数字的大小
[root@shell day3]# cat diff.sh #!/bin/sh if [ $# -ne 2 ];then echo "请输入两个数字" exit 2 fi if [[ "$1" =~ ^[0-9]+$ && "$2" =~ ^[0-9]+$ ]];then if [ $1 -gt $2 ];then echo "$1>$2" elif [ $1 -lt $2 ];then echo "$1<$2" else echo "$1=$2" fi else echo "请输入整数" exit 4 fi
案例2： 根据操作系统版本号安装不同的YUM源
[root@shell ~]# cat yum.sh #!/bin/bash #Author:ajie #Time:2020-04-11 11:17:50 Centos=`cat /etc/redhat-release |awk '{print $4}'|awk -F. '{print $1}'` which wget &>/dev/null if [ $? -ne 0 ] then echo "yum installed ..." yum install wget -y &>/dev/null if [ $? -eq 0 ] then echo "wget installed..." else echo "internet is not found.." fi if [ $Centos = "7" ] then wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo &>/dev/null if [ $? -eq 0 ] then echo "yum is ok" else echo "yum is error plaese check your network" fi else wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo &>/dev/null if [ $? -eq 0 ] then echo "yum is ok" else echo "yum is error please check your network" fi fi fi
案例3： 根据需求安装不同的版本服务
[root@shell ~]# cat /server/scripts/login.sh #!/bin/bash a7 () { echo -e " --------------" echo -e " 1.运维人员登录" echo -e " 2.开发人员登录" echo -e " --------------" } yunwei () { echo -e " welcome 运维" echo -e " 1.install PHP" echo -e " 2.install Nginx" echo -e " 3.install MySQL" echo -e " 4.install Java" echo -e " 5.install Python" echo -e " 6.install Docker" echo -e " 7.install K8s" } kaifa () { echo -e " welcome 开发" echo -e " 1.install PHP" echo -e " 2.install MySQL" echo -e " 3.install Java" echo -e " 4.install Python" } a1 () { echo -e " 1.install PHP5.5" echo -e " 2.install PHP5.6" echo -e " 3.install PHP5.7" } a2 () { echo -e " 1.install MySQL5.5" echo -e " 2.install MySQL5.6" echo -e " 3.install MySQL5.7" } a3 () { echo -e " 1.install JDK8" echo -e " 3.install JDK9" echo -e " 2.install JDK10" echo -e " 3.install JDK11" echo -e " 4.install JDK12" } a4 () { echo -e " 1.install Python3.4.2" echo -e " 3.install Python3.5.2" echo -e " 2.install Python3.6.2" echo -e " 3.install Python3.7.2" } a7 while true do read -p "Choose your login: " num if [ $num -eq 1 ];then read -p "Input your psaaword: " passwd if [ "$passwd" == "yunwei" ];then yunwei fi read -p "Select the corresponding operation: " number if [ $number -eq 1 ];then echo "install PHP..." && a7 elif [ $number -eq 2 ];then echo "install Nginx..." && a7 elif [ $number -eq 3 ];then echo "install MySQL..." && a7 elif [ $number -eq 4 ];then echo "install Java..." && a7 elif [ $number -eq 5 ];then echo "install Python..." && a7 elif [ $number -eq 6 ];then echo "install Docker..." && a7 elif [ $number -eq 7 ];then echo "install K8s..." && a7 else echo "no server " && exit fi elif [ $num -eq 2 ];then read -p "Input your psaaword: " passwd if [ "$passwd" == "kaifa" ];then kaifa fi read -p "Choose your login: " number if [ $number -eq 1 ];then a1 read -p "Choose your server: " n if [ $n -eq 1 ];then echo "install PHP5.5..." && a7 elif [ $n -eq 2 ];then echo "install PHP5.6..." && a7 elif [ $n -eq 3 ];then echo "install PHP5.7..." && a7 fi elif [ $number -eq 2 ];then a2 read -p "Choose your server: " n if [ $n -eq 1 ];then echo "install MySQL5.5..." && a7 elif [ $n -eq 2 ];then echo "install MySQL5.6..." && a7 elif [ $n -eq 3 ];then echo "install MySQL5.7..." && a7 fi elif [ $number -eq 3 ];then a3 read -p "Choose your server: " n if [ $n -eq 1 ];then echo "install JDK8..." && a7 elif [ $n -eq 2 ];then echo "install JDK9..." && a7 elif [ $n -eq 3 ];then echo "install JDK10..." && a7 elif [ $n -eq 2 ];then echo "install JDK11..." && a7 elif [ $n -eq 3 ];then echo "install JDK12..." && a7 fi elif [ $number -eq 4 ];then a4 read -p "Choose your server: " n if [ $n -eq 1 ];then echo "install Python3.4.2" && a7 elif [ $n -eq 2 ];then echo "install Python3.5.2" && a7 elif [ $n -eq 3 ];then echo "install Python3.6.2" && a7 elif [ $n -eq 2 ];then echo "install Python3.7.2" && a7 fi else exit fi else echo "The password is error" && exit fi done