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<h1><center>流程控制</center></h1>
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作者：行癫（盗版必究）
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------
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## 一：条件测试
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#### 1.语法格式
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```shell
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格式1： test 条件表达式
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格式2： [ 条件表达式 ]
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格式3： [[ 条件表达式 ]]
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```
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#### 2.文件测试
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```shell
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[ -e dir|file ]
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[ -d dir ]
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[ -f file ] 是否存在，而且是文件
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[ -r file ] 当前用户对该文件是否有读权限
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[ -x file ]
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[ -w file ]
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```
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案例
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```shell
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[root@xingdian ~]# test -d /home
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[root@xingdian ~]# echo $?
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0
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[root@xingdian ~]# test -d /home11111
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[root@xingdian ~]# echo $?
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1
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[root@xingdian ~]# [ -d /home ]
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[root@xingdian ~]# [ ! -d /ccc ] && mkdir /ccc
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[root@xingdian ~]# [ -d /ccc ] || mkdir /ccc
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```
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#### 3.数值比较
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```shell
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[ 1 -gt 10 ] 大于
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[ 1 -lt 10 ] 小于
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[ 1 -eq 10 ] 等于
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[ 1 -ne 10 ] 不等于
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[ 1 -ge 10 ] 大于等于
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[ 1 -le 10 ] 小于等于
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```
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案例
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```shell
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[root@xingdian ~]# disk_use=$(df -P |grep '/$' |awk '{print $5}' |awk -F% '{print $1}')
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[root@xingdian ~]# [ $disk_use -gt 90 ] && echo "war......"
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[root@xingdian ~]# [ $disk_use -gt 60 ] && echo "war......"
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```
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```shell
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[root@xingdian ~]# [ $(id -u) -eq 0 ] && echo "当前是超级用户"
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当前是超级用户
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[alice@xingdian ~]$ [ $UID -eq 0 ] && echo "当前是超级用户" || echo "you不是超级用户"
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you不是超级用户
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```
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#### 4.字符串比较
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```shell
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提示：使用双引号
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[root@xingdian ~]# [ "$USER" = "root" ];echo $?
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0
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[root@xingdian ~]# [ "$USER" == "root" ];echo $?
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0
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```
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注意：
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```shell
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""：弱引用，可以实现变量和命令的替换
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[root@xingdian ~]# x=*
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[root@xingdian ~]# echo "$x"
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*
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''：强引用，不完成变量替换
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[root@xingdian ~]# x=*
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[root@xingdian ~]# echo '$x'
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$x
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```
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#### 5.扩展
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```shell
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[root@xingdian ~]# var1=111
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[root@xingdian ~]# var2=
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[root@xingdian ~]# //var3变量没有定义
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[root@xingdian ~]# echo ${#var1} #显示变量中字符串的个数
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3
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[root@xingdian ~]# echo ${#var2}
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0
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[root@xingdian ~]# echo ${#var3}
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0
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[root@xingdian ~]# [ -z "$var1" ];echo $? //-z 变量字符串为空
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1
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[root@xingdian ~]# [ -z "$var2" ];echo $?
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0
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[root@xingdian ~]# [ -z "$var3" ];echo $?
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0
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[root@xingdian ~]# [ -n "$var1" ];echo $? //-n 变量字符串不为空
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0
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[root@xingdian ~]# [ -n "$var2" ];echo $?
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1
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[root@xingdian ~]# [ -n "$var3" ];echo $?
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1
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```
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案例：
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```shell
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[root@xingdian ~]# [ "$USER" = "root" ];echo $?
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0
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[root@xingdian ~]# [ "$USER" = "alice" ];echo $?
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1
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[root@xingdian ~]# [ "$USER" != "alice" ];echo $?
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0
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[root@xingdian ~]# [ 1 -lt 2 -a 5 -gt 10 ];echo $?
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1
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[root@xingdian ~]# [ 1 -lt 2 -o 5 -gt 10 ];echo $?
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0
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[root@xingdian ~]# [[ 1 -lt 2 && 5 -gt 10 ]];echo $?
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1
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[root@xingdian ~]# [[ 1 -lt 2 || 5 -gt 10 ]];echo $?
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0
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[root@xingdian ~]# [ "$USER" = "root" ];echo $?
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0
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```
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## 二：条件判断
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#### 1.流程控制
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在一个shell脚本中的命令执行顺序称作脚本的流；大多数脚本会根据一个或多个条件来改变它们的流
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流控制命令：能让脚本的流根据条件而改变的命令称为条件流控制命令
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exit语句：退出程序的执行，并返回一个返回码，返回码为0正常退出，非0为非正常退出
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条件判断：if代码返回0表示真，非0为假
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#### 2.语法结构
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单分支结构
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```shell
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if 条件测试
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then 命令序列
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fi
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```
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双分支结构
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```shell
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if 条件测试
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then 命令序列
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else 命令序列
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fi
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```
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多分支结构
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```shell
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if 条件测试1
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then 命令序列
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[elif 条件测试2
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then 命令序列
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elif 条件测试3
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then 命令序列]...
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else 命令序列
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fi
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```
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案例
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```shell
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if [ "$USER" = "root" ]
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then
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if [ $UID -eq 0 ]
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then
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echo "the user is root"
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fi
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elif
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echo "……"
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elif
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echo "……"
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else
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echo "the user is not root"
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echo "正在给用户授权"
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fi
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```
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## 三：循环结构
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#### 1.for循环
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##### 语法结构
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```shell
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for i in (取值) 范围{1..20} zhangsan lisi wanger mazi ${array[*]}
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for 变量名 [ in 取值列表 ]
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do
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循环体
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done
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```
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##### 案例一
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```shell
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#!/bin/bash
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# ping主机测试
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for i in {70..100}
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do
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ping -c1 10.30.161.$i &> /dev/null
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if [ $? -eq 0 ]
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then
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echo "10.30.161.$i is up" |tee -a ipup.txt
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else
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echo "10.30.161.$i is down" |tee -a ipdown.txt
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fi
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done
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```
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##### 案例二
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```shell
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#!/usr/bin/env bash
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#批量添加账户
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for i in {30..40}
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do
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useradd user$i && echo "123" | passwd --stdin user$i &>/dev/null
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if [ $? -eq 0 ];then
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echo "账户 user$i 添加成功"
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else
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echo "账户 user$i 添加失败"
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fi
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done
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```
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##### 案例三
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```shell
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#!/usr/bin/env bash
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#批量删除账户
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for i in {20..30}
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do
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userdel -r user$i &>/dev/null
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[ $? -eq 0 ] && echo "账户 user$i 删除成功" || echo "账户 user$i 删除失败"
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done
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```
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#### 2.while循环
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不断重复的执行循环体中的语句，直到某个条件成立
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循环次数不一定是固定的
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##### 语法结构
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当条件测试成立（条件测试为真），执行循环体
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```
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while 条件测试
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do
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循环体
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done
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```
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##### 案例
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```shell
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echo "please enter a number between 5 and 10 :"
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read var
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while [[ $var != 0 ]]
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do
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if [ "$var" -lt 5 ]
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then
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echo "Too smail , Try again"
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read var
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elif [ "$var" -gt 10 ]
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then
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echo "Too big , Try again"
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read var
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else
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echo "Congratulation! You are right."
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exit 0;
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fi
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done
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```
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#### 3.until循环
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当条件测试成立（条件测试为假），执行循环体
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##### 语法结构
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```shell
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until 条件测试
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do
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循环体
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done
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```
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##### 案例
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```shell
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#!/bin/bash
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i=1
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until [ "$i" -eq 21 ]
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do
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userdel -r user$i
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let i++
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done
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```
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## 四：匹配模式
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#### 1.语法模式
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```shell
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read -p "请输入你的选项：" num
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case num in
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1) 选项
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命令序列1 命令/if语句/for循环……
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;;
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模式2)
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命令序列2
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;;
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模式3)
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命令序列3
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;;
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*)
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无匹配后命令序列
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esac
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```
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##### 案例一
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确定要继续删除吗 yes/no: " yes
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##### 案例二
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系统管理工具箱
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```shell
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Command action
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h 显示命令帮助
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f 显示磁盘分区
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d 显示磁盘挂载
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m 查看内存使用
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u 查看系统负载
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q 退出程序
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Command (h for help): m
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total used free shared buffers cached
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Mem: 7628 840 6788 0 29 378
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Swap: 2047 0 2047
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```
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#### 2.工具箱
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```shell
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#!/usr/bin/env bash
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cat <<-EOF
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+-------------------------------------------------------------------------+
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| System_tools V1.0 |
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+-------------------------------------------------------------------------+
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| a. Stop And Disabled Firewalld. |
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| b. Disabled SELinux Secure System. |
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| c. Install Apache Service. |
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| d. Quit |
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+-------------------------------------------------------------------------+
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EOF
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printf "\e[1;31m Please input your select: \e[0m" && read var
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case "$var" in
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"a")
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systemctl stop firewalld && systemctl disable firewalld
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;;
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"b")
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sed -ri s/SELINUX=enforcing/SELINUX=disabled/g /etc/selinux/config
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;;
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"c")
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yum -y install httpd httpd-tools
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;;
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"d")
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exit
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;;
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*)
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printf "请按照上方提供的选项输入!!!\n"
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;;
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esac
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```
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## 五：循环控制
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#### 1.break
|
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关键字用于跳出循环，执行循环后面的语句
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|
案例
|
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```shell
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for i in {1..10}
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do
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if [ $i -eq 5 ]
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then
|
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break
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fi
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echo $i
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done
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# 输出结果为：
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# 1
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# 2
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# 3
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# 4
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```
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#### 2.continue
|
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|
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跳过当前循环中的剩余语句，直接进入下一次循环
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|
|
|
案例
|
|
|
|
|
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```shell
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for i in {1..10}
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do
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if [ $i -eq 5 ]
|
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|
then
|
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|
continue
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|
fi
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echo $i
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|
done
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|
# 输出结果为：
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# 1
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# 2
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# 3
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# 4
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# 6
|
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# 7
|
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|
# 8
|
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# 9
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# 10
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```
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|
#### 3.sleep
|
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|
|
sleep 10 等待10秒，再继续下一操作
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|
|
## 六：格式化打印
|
|
|
|
|
|
printf 使用引用文本或空格分隔的参数，外面可以在 printf 中使用格式化字符串，还可以制定字符串的宽度、左右对齐方式等
|
|
|
|
|
|
#### 1.语法格式
|
|
|
|
|
|
```shell
|
|
|
[root@xingdiancloud ~]# printf format-string [arguments...]
|
|
|
• format-string: 为格式控制字符串
|
|
|
• arguments: 为参数列表
|
|
|
```
|
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|
|
|
```shell
|
|
|
[root@xingdiancloud ~]# echo "Hello, Shell"
|
|
|
Hello, Shell
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|
[root@xingdiancloud ~]# printf "Hello, Shell"
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|
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[root@xingdiancloud ~]# printf "Hello, Shell\n"
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|
Hello, Shell
|
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|
```
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|
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|
#### 2.案例
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|
|
|
|
```shell
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#!/bin/bash
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printf "%-10s %-8s %-4s\n" 姓名 性别 体重kg
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|
printf "%-10s %-8s %-4.2f\n" 张三 男 66.1234
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|
printf "%-10s %-8s %-4.2f\n" 李四 男 48.6543
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|
printf "%-10s %-8s %-4.2f\n" 郭芙 女 47.9876
|
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|
```
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|
|
|
|
|
#### 3.参数解释
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|
|
|
|
|
%s 字符串
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|
|
|
|
|
%f 小数
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|
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|
|
%d 数字
|
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|
|
|
|
%-10s 指一个宽度为10个字符（-表示左对齐，没有则表示右对齐）
|
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|
|
|
|
%-4.2f 指格式化为小数，其中.2指保留2位小数
|
|
|
|
|
|
\f 换页
|
|
|
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|
|
\n 换行
|
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|
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|
|
\r 回车
|
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|
|
|
|
## 七：颜色
|
|
|
|
|
|
shell脚本中echo显示内容带颜色显示，需要使用到-e参数
|
|
|
|
|
|
#### 1.语法格式
|
|
|
|
|
|
```shell
|
|
|
格式1：echo -e "\033[背景颜色;字体颜色m 要输出的字符 \033[0m"
|
|
|
格式2：echo -e "\e[背景颜色;字体颜色m 要输出的字符 \e[0m"
|
|
|
```
|
|
|
|
|
|
#### 2.案例
|
|
|
|
|
|
```shell
|
|
|
echo -e “\033[30m 黑色字 \033[0m”
|
|
|
echo -e “\033[31m 红色字 \033[0m”
|
|
|
echo -e “\033[32m 绿色字 \033[0m”
|
|
|
echo -e “\033[33m 黄色字 \033[0m”
|
|
|
echo -e “\033[34m 蓝色字 \033[0m”
|
|
|
echo -e “\033[35m 紫色字 \033[0m”
|
|
|
echo -e “\033[36m 天蓝字 \033[0m”
|
|
|
echo -e “\033[37m 白色字 \033[0m”
|
|
|
echo -e “\033[40;37m 黑底白字 \033[0m”
|
|
|
echo -e “\033[41;37m 红底白字 \033[0m”
|
|
|
echo -e “\033[42;37m 绿底白字 \033[0m”
|
|
|
echo -e “\033[43;37m 黄底白字 \033[0m”
|
|
|
echo -e “\033[44;37m 蓝底白字 \033[0m”
|
|
|
echo -e “\033[45;37m 紫底白字 \033[0m”
|
|
|
echo -e “\033[46;37m 天蓝底白字 \033[0m”
|
|
|
echo -e “\033[47;30m 白底黑字 \033[0m”
|
|
|
|
|
|
控制选项：
|
|
|
\033[0m：关闭所有属性
|
|
|
\033[1m：高亮显示，加粗
|
|
|
\033[5m：闪烁
|
|
|
```
|
