一、if条件语句的知识与实践
1.if条件语句语法（单分支结构）
第一种：
if < 条件表达式 > then 指令fi
第二种：
if < 条件表达式 >; then 指令fi
嵌套：
if < 条件表达式 > then if < 条件表达式 > then 指令 fifi
2.多分支结构
if < 条件表达式 > then 指令else 指令fi
if < 条件表达式 > then 指令elif < 条件表达式 > then 指令else 指令fi
3.单分支实践
（1）把下面的测试文件中条件表达式语句改成if条件语句
[root@codis-178 ~]# [ -f /etc/hosts ] && echo 11[root@codis-178 ~]# [[ -f /etc/hosts ]] && echo 11[root@codis-178 ~]# test -f /etc/hosts && echo 11
[root@codis-178 ~]# cat 7_1.sh #!/bin/bashif [ -f /etc/hosts ] then echo 1fiif [[ -f /etc/hosts ]] then echo 1fiif test -f /etc/hosts then echo 1fi[root@codis-178 ~]# sh 7_1.sh 111
（2）判断系统剩余内存大小，若低于100MB。就邮件报警，并将脚本加入定时任务，每3分钟执行一次检查。
[root@codis-178 ~]# cat 7_2.sh#!/bin/bashFreeMem=`free -m|awk 'NR==3 {print $NF}'`CHARS="Current memory is $FreeMem"if [ $FreeMem -lt 100 ] then echo $CHARS|tee /tmp/messages.txt mail -s "`date +%F-%T`$CHARS" test@oldboy.com < /tmp/messages.txtfi加入crontab中# monitor sys mem at 20170802 by xiaoda*/3 * * * * /bin/sh /data/cron/7_2.sh &>/dev/null （3）实现整数大小的比较
[root@codis-178 ~]# cat 7_3.sh #!/bin/bashread -p "pls input two num:" a bif [ $a -lt $b ];then echo "$a < $b"elif [ $a -gt $b ];then echo "$a > $b"elif [ $a -eq $b ];then echo "$a = $b"else echo "Input error"fi[root@codis-178 ~]# sh 7_3.shpls input two num: 5 65 < 6[root@codis-178 ~]# sh 7_3.shpls input two num: 8 48 > 4[root@codis-178 ~]# sh 7_3.shpls input two num: 5 55 = 5
二、企业案例
1.监控Web和数据库之分析问题
2.监控方法
本地端口监控
netstat -lnt|grep 3306|awk -F "[ :]+" '{print $5}'netstat -lntup|grep 3306 |wc -lnetstat -lntup|grep mysql|wc -llsof -i tcp:3306|wc -l 远程端口监控
nmap 127.0.0.1 -p 3306 |grep open |wc -lnc -w 2 127.0.0.1 3306 &>/dev/null
服务进程或进程数监控
ps -ef|grep mysql|grep -v grep|wc -l
客户端模拟用户访问
[root@codis-178 ~]# wget --spider --timeout=10 --tries=2 www.baidu.comSpider mode enabled. Check if remote file exists.--2017-08-02 13:55:10-- http://www.baidu.com/Resolving www.baidu.com... 61.135.169.125, 61.135.169.121Connecting to www.baidu.com|61.135.169.125|:80... connected.HTTP request sent, awaiting response... 200 OKLength: 277 [text/html]Remote file exists and could contain further links,but recursion is disabled -- not retrieving.
curl -s http://www.baidu.com
3.开发监控MySQL数据库的脚本
[root@codis-178 ~]# cat 7_4.sh #!/bin/bashecho method1--------------if [ `netstat -lnt|grep 3306|awk -F "[ :]+" '{print $5}'` -eq 3306 ] then echo "MySQL is Running."else echo "MySQL is Stopped." #/etc/init.d/mysqld startfi[root@codis-178 ~]# sh 7_4.sh method1--------------MySQL is Running.[root@codis-178 ~]# cat 7_4_1.sh#!/bin/bashecho method2--------------if [ `netstat -lnt|grep 3306|awk -F "[ :]+" '{print $5}'` = "3306" ] then echo "MySQL is Running."else echo "MySQL is Stopped." #/etc/init.d/mysqld startfi[root@codis-178 ~]# sh 7_4_1.shmethod2--------------MySQL is Running.[root@codis-178 ~]# cat 7_4_2.sh #!/bin/bashecho method3--------------if [ `netstat -lntup|grep mysqld|wc -l` -gt 0 ] then echo "MySQL is Running."else echo "MySQL is Stopped." #/etc/init.d/mysqld startfi[root@codis-178 ~]# sh 7_4_2.sh method3--------------MySQL is Running.[root@codis-178 ~]# cat 7_4_3.sh #!/bin/bashecho method4--------------if [ `lsof -i tcp:3306|wc -l` -gt 0 ] then echo "MySQL is Running."else echo "MySQL is Stopped." #/etc/init.d/mysqld startfi[root@codis-178 ~]# sh 7_4_3.sh method4--------------MySQL is Running. 4.监控Nginx Web服务异常
[root@codis-178 ~]# netstat -lnt|grep -w 8081|awk -F "[ :]+" '{print $5}'8081[root@codis-178 ~]# netstat -lntup|grep -w 8081|wc -l1[root@codis-178 ~]# lsof -i tcp:8081|wc -l4 [root@codis-178 ~]# ps -ef |grep nginx|grep -v grep|wc -l3[root@codis-178 ~]# ps -C nginx --no-header10869 ? 00:00:00 nginx10870 ? 00:10:55 nginx10871 ? 00:07:43 nginx[root@codis-178 ~]# ps -C nginx --no-header|wc -l3
5.开发监控Nginx Web服务的脚本
[root@codis-178 ~]# cat 7_5.sh #!/bin/bashecho http method1---------------if [ `netstat -lnt|grep 8081|awk -F "[ :]+" '{print $5}'` -eq 8081 ] then echo "Nginx is Running."else echo "Nginx is Stoped."fi[root@codis-178 ~]# sh 7_5.sh http method1---------------Nginx is Running.[root@codis-178 ~]# cat 7_5_1.sh #!/bin/bashecho http method1---------------if [ `netstat -lnt|grep 8081|awk -F "[ :]+" '{print $5}'` = "8081" ] then echo "Nginx is Running."else echo "Nginx is Stoped."fi[root@codis-178 ~]# sh 7_5_1.sh http method1---------------Nginx is Running.[root@codis-178 ~]# cat 7_5_2.sh #!/bin/bashecho http method2---------------if [ `netstat -lntup|grep nginx|wc -l` -gt 0 ] then echo "Nginx is Running."else echo "Nginx is Stoped."fi[root@codis-178 ~]# sh 7_5_2.sh http method2---------------Nginx is Running. 三、经典案例
1.比较两个整数
[root@codis-178 ~]# cat 7_6.sh#!/bin/bashread -p "pls input two num:" a bexpr $a + 10 &>/dev/nullRETVAL1=$?expr $b + 10 &>/dev/nullRETVAL2=$?if [ -z "$a" ] || [ -z "$b" ] then echo "Pls input two num agin." exit 1elif test $RETVAL1 -ne 0 -o $RETVAL2 -ne 0 then echo "Pls input two "num" again." exit 2elif [ $a -lt $b ] then echo "$a < $b"elif [ $a -eq $b ] then echo "$a = $b"else echo "$a > $b"fi[root@codis-178 ~]# sh 7_6.shpls input two num: 6 96 < 9[root@codis-178 ~]# sh 7_6.shpls input two num: 8 28 > 2[root@codis-178 ~]# sh 7_6.shpls input two num: 7 77 = 7
2.判断字符串是否为数字
思路1：删除字符串中的所有数字，看长度是否为0[root@codis-178 ~]# [ -n "`echo oldboy123|sed 's/[0-9]//g'`" ] && echo char ||echo intchar[root@codis-178 ~]# [ -n "`echo 123|sed 's/[0-9]//g'`" ] && echo char ||echo intint[root@codis-178 ~]# [ -z "`echo 123|sed 's/[0-9]//g'`" ] && echo char ||echo intchar[root@codis-178 ~]# [ -z "`echo 123|sed 's/[0-9]//g'`" ] && echo int ||echo charint[root@codis-178 ~]# [ -z "`echo oldboy123|sed 's/[0-9]//g'`" ] && echo int ||echo charchar思路2：如果num的长度不为0，并且把num中的非数字部分删除，然后再看结果是不是等于num本身，如果两者都成立，则num是数字[root@codis-178 ~]# num=521[root@codis-178 ~]# [ -n "$num" -a "$num" = "${num//[^0-9]/}" ] && echo "it is num"it is num[root@codis-178 ~]# num=oldboy521[root@codis-178 ~]# [ -n "$num" -a "$num" = "${num//[^0-9]/}" ] && echo "it is num"[root@codis-178 ~]# 思路3：通过expr计算判断[root@codis-178 ~]# expr pldboy + 1 &>/dev/null[root@codis-178 ~]# echo $?2[root@codis-178 ~]# expr 123 + 1 &>/dev/null[root@codis-178 ~]# echo $?0[root@codis-178 ~]# expr 0 + 0 &>/dev/null[root@codis-178 ~]# echo $?1思路4：利用“=~”符号判断[root@codis-178 ~]# [[ oldboy123 =~ ^[0-9]+$ ]] && echo int ||echo charchar[root@codis-178 ~]# [[ 123 =~ ^[0-9]+$ ]] && echo int ||echo charint 3.判断字符串长度是否为0
思路1：使用-z和-n的语法[root@codis-178 ~]# [ -z "oldboy" ] && echo 1 ||echo 00[root@codis-178 ~]# [ -n "oldboy" ] && echo 1 ||echo 01思路2：使用变量子串判断[root@codis-178 ~]# [ ${#char} -eq 0 ] && echo 1 ||echo 00思路3：使用expr length函数判断[root@codis-178 ~]# [ `expr length "oldboy"` -eq 0 ] && echo 1 || echo 00思路4：使用wc的-L参数统计[root@codis-178 ~]# [ `echo oldboy|wc -L` -eq 0 ] && echo 1 ||echo 00思路5：使用awk length函数判断[root@codis-178 ~]# [ `echo oldboy|awk '{print length}'` -eq 0 ] && echo 1 || echo 00 4.生产场景案例
（1）监控memcached服务
[root@codis-178 ~]# cat memcached.sh #!/bin/bashprintf "del key\r\n"|nc 127.0.0.1 11211 &>/dev/nullprintf "set key 0 0 10 \r\noldboy1234\r\n"|nc 127.0.0.1 11211 &>/dev/nullMcValues=`printf "get key\r\n" |nc 127.0.0.1 11211|grep oldboy1234|wc -l`if [ $McVaules -eq 1 ] then echo "memcached status is ok."else echo "memcached status is bad."fi
思考题：如何监控MC服务、命中率、响应时间三个指标
（2）开发rsync启动脚本
[root@codis-178 ~]# cat rsyncd#!/bin/bash# chkconfig: 2345 20 80# description: Rsyncd Startup script by xiaodaif [ $# -ne 1 ] then echo $"usage:$0 {start|stop|restart}" exit 1fiif [ "$1" = "start" ] then rsync --daemon sleep 2 if [ `netstat -lntip|grep rsync|wc -l` -ge 1 ] then echo "rsyncd is started." exit 0 fielif [ "$1" = "stop" ] then killall rsync &>/dev/null sleep 2 if [ `netstat -lntip|grep rsync|wc -l` -eq 0 ] then echo "rsyncd is stoped." exit 0 fielif [ "$1" = "restart" ] then killall rsync sleep 1 killpro=`netstat -lntup|grep rsync |wc -l` rsync --daemon sleep 1 startpro=`netstat -lntup|grep rsync |wc -l` if [ $killpro -eq 0 -a $startpro -ge 1 ] then echo "rsync is restarted." exit 0 fielse echo $"usage:$0 {start|stop|restart}" exit 1fi 运行结果：
[root@codis-178 ~]# /etc/init.d/rsyncd stoprsyncd is stoped.[root@codis-178 ~]# netstat -lntup |grep 873[root@codis-178 ~]# /etc/init.d/rsyncd start[root@codis-178 ~]# netstat -lntup |grep 873tcp 0 0 192.168.1.178:873 0.0.0.0:* LISTEN 13878/rsync