Shell编程实战-if条件语句

总结

方法

01、单分支结构：

if <条件表达式>
 then
  指令
if
或
if <条件表达式>;then
  指令
if

02、嵌套：

if <条件表达式>
 then
  if <条件表达式>
   then
    指令
  if
if

03、双分支结构：

if <条件表达式>;then
  指令
else
  指令
if

04、多分支结构：

if <条件表达式>;then
  指令
elif <条件表达式>;then
  指令
else
  指令
if

05、监控MySQL数据库：

if [ `netstat -lntup|grep mysqld|wc -l` -gt 0 ];then
	echo "MySQL is Running."
else
	echo "MySQL is Stopped."
	/etc/init.d/mysqld start
fi

06、监控Nginx Web服务：

if [ `netstat -lntup|grep nginx|wc -l` -gt 0 ];then
	echo "Nginx is Running."
else
	echo "Nginx is Stopped."
	/etc/init.d/nginx start
fi 

07、判断字符串是否为数字：[ -n "`echo oldboy123|sed 's/[]0-9//g'`" ]&&echo char||echo int

08、[ -z "`echo oldboy123|sed 's/[]0-9//g'`" ]&&echo int||echo char

09、num=521;[ -n "$num" -a "$num" = "${num//[^0-9]/}" ]&&echo "num"

10、[[ oldboy123 =~ ^[0-9]+$ ]]&&echo int||echo char

11、监控memcached服务：

#!/bin/sh
printf "del key\r\n"|nc 127.0.0.1 11211 &>/dev/null
printf "set key  0 0 10 \r\noldboy1234\r\n"|nc 127.0.0.1 11211 &>/dev/null
McValues=`printf "get key\r\n"|nc 127.0.0.1 11211|grep oldboy1234|wc -l`
if [ $McValues -eq 1 ];then
	echo "memcached status is ok"
else
	echo "memcached status is bad"
fi

12、rsync服务的启动脚本：cat /etc/init.d/rsyncd

#!/bin/bash
if [ $# -ne 1 ];then
	echo $"usage:$0 {start|stop|restart}"
	exit 1
fi
if [ "$1" = "start" ];then
	rsync --daemon
	sleep 2
	if [ `netstat -lntup|grep rsync|wc -l` -ge 1 ];then
		echo "rsyncd is started."
		exit 0
	fi
elif [ "$1" = "stop" ];then
	killall rsync &>/dev/null
	sleep 2
	if [ `netstat -lntup|grep rsync|wc -l` -eq 0 ];then
		echo "rsyncd is stopped."
		exit 0
	fi
elif [ "$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 "rsyncd is restarted."
		exit 0
	fi
else
	echo $"usage:$0 {start|stop|restart}"
	exit 1
fi

13、rsync的启动脚本：cat /etc/init.d/rsyncd

#!/bin/bash 
# chkconfig: 2345 20 80 
# description: Rsyncd Startup scripts by oldboy.
if [ $# -ne 1 ];then
	echo $"usage:$0 {start|stop|restart}"
	exit 1
fi
if [ "$1" = "start" ];then
	rsync --daemon
	sleep 2
	if [ `netstat -lntup|grep rsync|wc -l` -ge 1 ];then
		echo "rsyncd is started."
		exit 0
	fi
elif [ "$1" = "stop" ];then
	killall rsync &>/dev/null
	sleep 2
	if [ `netstat -lntup|grep rsync|wc -l` -eq 0 ];then
		echo "rsyncd is stopped."
		exit 0
	fi
elif [ "$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 "rsyncd is restarted."
		exit 0
	fi
else
	echo $"usage:$0 {start|stop|restart}"
	exit 1
fi
----------
chkconfig --list rsyncd
chkconfig --add rsyncd
chkconfig --list rsyncd