shell if 条件语句实践

对于if 语法 我们不过多做介绍，这里直接上实例，以开发rsync服务启动脚本为例，先对rsync做个简单介绍

[root@backup ~]# rpm -qa|grep rsync
rsync-3.0.-.el6.x86_64
[root@backup ~]#
[root@backup ~]# cat /etc/rsync
rsyncd.conf     rsync.password
[root@backup ~]# cat /etc/rsyncd.conf
#Rsync server
uid = rsync
gid = rsync
use chroot = no
max connections =
timeout =
pid file = /var/run/rsyncd.pid
lock file = /var/run/rsync.lock
log file = /var/log/rsyncd.log
ignore errors
read only = false
list = false
hosts allow = 172.16.80.0/
hosts deny = 0.0.0.0/
auth users = rsync_backup
secrets file = /etc/rsync.password
###########
[backup]
comment = backup by martin
path = /backup

[root@backup ~]# cat /etc/rsync
rsyncd.conf     rsync.password
[root@backup ~]# cat /etc/rsync.password
rsync_backup:
[root@backup ~]#
[root@backup ~]# rsync --daemon   #启动rsync
[root@backup ~]# netstat -lntup|grep rsync
tcp               0.0.0.0:                 0.0.0.0:*                   LISTEN      /rsync
tcp               :::                      :::*                        LISTEN      /rsync     

[root@backup ~]# pkill rsync  #停止rsync
[root@backup ~]# netstat -lntup|grep rsync

判断rsync服务是否启动的方法

常规方法有检测端口以及进程是否存在，可以当服务启动时，创建一个锁文件 /var/lock/subsys/  而当服务停止时，就删除这个锁文件，这样就可以通过判断这个文件有无来确定服务是否是启动的状态，这是一些系统脚本常用的手法，脚本开发如下

[root@backup ~]# cat rsyncd.sh
#!/bin/bash
# chkconfig:   80
# 2345是linux的启动运行级别，20表示开始启动顺序，80表示脚本停止顺序，这两个数字都是不超过99的数字，应用服务一般要考后启动为佳，越早停止越好
if [ $# -ne  ];then
    echo  $"usage: $0 {start|stop|restart}"
    exit
fi

if [ "$1" = "start" ];then
    rsync --daemon
    sleep
    if [ `netstat -lntup|grep rsync|wc -l` -ge  ];then
        echo "rsyncd is started."
    fi

elif [ "$1" = "stop" ];then
    pkill rsync &>/dev/null
    sleep
    if [ `netstat -lntup|grep rsync|wc -l` -eq  ];then
        echo "rsyncd is stopped."
    fi

elif [ "$1" = "restart" ];then
    pkill rsync
    sleep
    killpro=`netstat -lntup|grep rsync|wc -l`
    rsync --daemon
    sleep
    startpro=`netstat -lntup|grep rsync|wc -l`
    if [ $killpro -eq  -a $startpro -ge  ];then
        echo "rsyncd is restarted."
    fi

else
   echo $"usage: $0 {start|stop|restart}"
   exit
fi
[root@backup ~]#
[root@backup ~]#
[root@backup ~]# ps -ef|grep rsync
root           : pts/    :: grep rsync
[root@backup ~]#
[root@backup ~]#
[root@backup ~]# sh rsyncd.sh start
rsyncd is started.
[root@backup ~]#
[root@backup ~]# ps -ef|grep rsync
root               : ?        :: rsync --daemon
root           : pts/    :: grep rsync
[root@backup ~]# netstat -lntup |grep rsync
tcp               0.0.0.0:                 0.0.0.0:*                   LISTEN      /rsync
tcp               :::                      :::*                        LISTEN      /rsync
[root@backup ~]#
[root@backup ~]# sh rsyncd.sh restart
rsyncd is restarted.
[root@backup ~]# netstat -lntup |grep rsync
tcp               0.0.0.0:                 0.0.0.0:*                   LISTEN      /rsync
tcp               :::                      :::*                        LISTEN      /rsync
[root@backup ~]# sh rsyncd.sh stop
rsyncd is stopped.
[root@backup ~]# netstat -lntup |grep rsync

使用shell函数封装的方法来优化上面的脚本，改良后的脚本如下

[root@backup ~]# cat /etc/init.d/rsyncd
#!/bin/sh
# chkconfig:
. /etc/init.d/functions

if [ $# -ne  ];then
   echo $"USAGE: $0 {start|stop|restart}"
   exit
fi

start(){
    rsync --daemon
    sleep
    if [ `netstat -lntup|grep rsync|wc -l` -ge  ];then
        action "rsyncd is started." /bin/true
    else
        action "rsyncd is stopped." /bin/false
    fi
}

stop(){
    killall rsync &>/dev/null
    sleep
    if [ `netstat -lntup|grep rsync|wc -l` -eq  ];then
        action "rsyncd is stopped." /bin/true
    else
        action "rsyncd is started." /bin/false
    fi
}

restart(){
    stop
    sleep
    start
}

case "$1" in
    start)
    start
    ;;
    stop)
    stop
    ;;
    restart)
    restart
    ;;
    *)
    echo "echo "USAGE: $ {start|stop|restart}""
esac