ssh 遍历IPS 进行连接

今天生产要批量连接服务器并执行命令：把所有的IP写到一个iplist文件，然后用while read 和for进行遍历拼接ssh命令发现两个问题：ssh连接参数-n 和while read与for读取的区别

脚本

iplist

192.168.4.12

192.168.4.13

192.168.4.14

tongjidf.sh

#!/bin/bash

cmd="df -m | grep app"

while read line

do

ssh [email protected]${line} $cmd

done <./iplist

执行的结果发现只连接了一个地址192.168.4.12、后面的地址没有执行

然后改成了for

#!/bin/bash

cmd="df -m|grep app"

for ips in `cat iplist`

do

ssh [email protected]${line} $cmd

done

这个脚本就可以实现连接以上所有地址然后进行命令执行。

终于找到了一个说法：就是for是一行一行的读取，而while read line是一次读取放入内存

第二个就是ssh默认读取本地的内容，而-n参数阻止了，而是从/dev/null/读取，这样一来ssh如果用while read line的形式就是连接一个

-n      Redirects stdin from /dev/null (actually, prevents reading from stdin).  This must be used when ssh is run in the background.  A
             common trick is to use this to run X11 programs on a remote machine.  For example, ssh -n shadows.cs.hut.fi emacs & will start
             an emacs on shadows.cs.hut.fi, and the X11 connection will be automatically forwarded over an encrypted channel.  The ssh pro-
             gram will be put in the background.  (This does not work if ssh needs to ask for a password or passphrase; see also the -f