Shell脚本应用if语句

Posted 2020-07-30

1. 单分支的if语句：
   

---

if 条件测试操作

then

 命令序列

fi

---

例：判断挂载点目录是否存在，若不存在则新建此目录。

---

[[email protected] script]# cat chkmountdir.sh 

#!/bin/bash

MOUNT_DIR="/media/cdrom"

if [ ! -d $MOUNT_DIR ]

then

mkdir -p $MOUNT_DIR

fi

[[email protected] script]# chmod +x chkmountdir.sh 

[[email protected] script]# ./chkmountdir.sh 

[[email protected] script]# ls /media/

cdrom  RHEL_6.5 x86_64 Disc 1

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例：若当前用户不是root，则提示报错：

---

[[email protected] script]# cat chkifroot.sh 

#!/bin/bash

if [ "$USER" != "root" ];then

echo "错误：非root用户，权限不足！"

exit 1

fi 

fdisk -l /dev/sda

[[email protected] script]# chmod +x chkifroot.sh 

[[email protected] script]# ./chkifroot.sh 

Disk /dev/sda: 53.7 GB, 53687091200 bytes

255 heads, 63 sectors/track, 6527 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x000e59bd

   Device Boot      Start         End      Blocks   Id  System

/dev/sda1   *           1          64      512000   83  Linux

Partition 1 does not end on cylinder boundary.

/dev/sda2              64        6528    51915776   8e  Linux LVM

[[email protected] script]# su - oracle

[[email protected] ~]$ source /script/chkifroot.sh 

错误：非root用户，权限不足！

---

2.双分支的if语句：

---

if  条件测试操作

then

 命令序列1

else

命令序列2

fi

---

例：编写一个连通性的测试脚本，通过位置参数$1提供目标主机地址。然后根据ping检测结果给出相应的提示。

---

[[email protected] script]# cat ping.sh 

#!/bin/bash

ping -c 3 -i  0.2 -W 3 $1 &> /dev/null

if [ $? -eq 0 ]

then 

echo "Host $1 is up."

else 

echo "Host $1 is down."

fi

[[email protected] script]# chmod +x ping.sh 

[[email protected] script]# ./ping.sh 192.168.1.11

Host 192.168.1.11 is up.

[[email protected] script]# ./ping.sh 192.168.1.12

Host 192.168.1.12 is down.

---

例：通过shell脚本检查httpd服务是否运行；

---

[[email protected] script]# cat chkhttpd.sh 

#!/bin/bash

/etc/init.d/httpd status &>/dev/null

if [ $? -eq  0 ];then

echo "监听地址:$(netstat -anpt |grep httpd | awk ‘{print $4}‘)"

echo "进程PID号：$(pgrep -x httpd)"

else

echo "警告：httpd服务不可用"

fi

[[email protected] script]# chmod +x chkhttpd.sh 

[[email protected] script]# ./chkhttpd.sh 

警告：httpd服务不可用

[[email protected] script]# service httpd start

[[email protected] script]# ./chkhttpd.sh 

监听地址::::80

进程PID号：2398

---

3.多分支if语句

---

if 条件测试操作1

then

命令序列1

elif 条件测试操作2

then

命令序列2

else

命令序列3

fi

---

例:编写一个成绩分档脚本；

---

[[email protected] script]# cat gradediv.sh 

#!/bin/bash

read -p "请输入你的成绩[0-100]:" GRADE

if [ $GRADE -ge 85 ] && [ $GRADE -le 100 ];then

echo "$GRADE 分！你分数很牛逼"

elif [ $GRADE -ge 70 ] && [ $GRADE -le 84 ];then

echo "$GRADE 分！还行吧小伙子"

else

echo "$GRADE 分！你是个垃圾"

fi

[[email protected] script]# chmod +x gradediv.sh 

[[email protected] script]# ./gradediv.sh 

请输入你的成绩[0-100]:100

100 分！你分数很牛逼

[[email protected] script]# ./gradediv.sh 

请输入你的成绩[0-100]:78

78 分！还行吧小伙子

[[email protected] script]# ./gradediv.sh 

请输入你的成绩[0-100]:50

50 分！你是个垃圾

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就到这吧，慢慢积累

本文出自 “一只菜的不能再菜的小菜鸟” 博客，请务必保留此出处http://liliming.blog.51cto.com/10925034/1793023