作者ubl007·2023-09-13 23:22

私有云高级交付（DTA方向）·百度智能云

通过 while循环体对远程主机进行遍历性ssh登录并执行目标指令

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内容摘要：

文章介绍了使用for循环替代while循环，解决ssh登录执行指令时的读取下一条记录问题。

当前摘要为AI生成

实现方法：

一  对 ssh 命令使用选项“-n”

二  使用 for循环遍历替代 while循环遍历

三  对 while 循环体使用 exec描述符

问题的表现现象：

while循环体只执行了目标文件中的第一行内容便推出循环了。
此现象也称作“while循环吃行现象”。

如以下实例所示：

[root@localhost centos7-00]# cat /etc/hosts

192.168.136.145 slave0

192.168.136.152 slave1

[root@localhost centos7-00]#

[root@localhost centos7-00]# cat /etc/hosts | while read hang;do server=`echo ${hang} | awk -F " " '{print $1}'` && name=`echo ${hang} | awk -F " " '{print $2}'` && ssh root@${server} "ip a";done

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: ens33:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:6d:22:15 brd ff:ff:ff:ff:ff:ff

inet 192.168.136.145/24 brd 192.168.136.255 scope global noprefixroute dynamic ens33

valid_lft 1143sec preferred_lft 1143sec

inet6 fe80::e212:a166:2a5:ffdc/64 scope link noprefixroute

valid_lft forever preferred_lft forever

3: virbr0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

valid_lft forever preferred_lft forever

4: virbr0-nic:  mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

[root@localhost centos7-00]# 
[root@localhost centos7-00]# vim test.sh

[root@localhost centos7-00]#

[root@localhost centos7-00]# cat test.sh

cat /etc/hosts | while read hang

server=`echo ${hang} | awk -F " " '{print $1}'`

name=`echo ${hang} | awk -F " " '{print $2}'`

ssh root@${server} "ip a"

done

[root@localhost centos7-00]#

[root@localhost centos7-00]# sh -x test.sh

+ cat /etc/hosts

+ read hang

++ echo 192.168.136.145 slave0

++ awk -F ' ' '{print $1}'

+ server=192.168.136.145

++ awk -F ' ' '{print $2}'

++ echo 192.168.136.145 slave0

+ name=slave0

+ ssh -n root@192.168.136.145 'ip a'

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: ens33:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:6d:22:15 brd ff:ff:ff:ff:ff:ff

inet 192.168.136.145/24 brd 192.168.136.255 scope global noprefixroute dynamic ens33

valid_lft 1642sec preferred_lft 1642sec

inet6 fe80::e212:a166:2a5:ffdc/64 scope link noprefixroute

valid_lft forever preferred_lft forever

3: virbr0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

valid_lft forever preferred_lft forever

4: virbr0-nic:  mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

+ read hang

++ echo 192.168.136.152 slave1

++ awk -F ' ' '{print $1}'

+ server=192.168.136.152

++ echo 192.168.136.152 slave1

++ awk -F ' ' '{print $2}'

+ name=slave1

+ ssh -n root@192.168.136.152 'ip a'

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: ens33:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:4c:90:50 brd ff:ff:ff:ff:ff:ff

inet 192.168.136.152/24 brd 192.168.136.255 scope global noprefixroute dynamic ens33

valid_lft 1421sec preferred_lft 1421sec

inet6 fe80::e212:a166:2a5:ffdc/64 scope link tentative noprefixroute dadfailed

valid_lft forever preferred_lft forever

inet6 fe80::1018:25e5:682e:fa55/64 scope link noprefixroute

valid_lft forever preferred_lft forever

3: virbr0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

valid_lft forever preferred_lft forever

4: virbr0-nic:  mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

+ read hang

[root@localhost centos7-00]#

产生此现象的原因：

while 使用了重定向机制，这个重定向是针对while循环快整体的，/etc/hosts 中的行信息被读取并重定向到了while循环块中，当while中再次调用read语句是就会读取到文件 /etc/hosts 中的下一条记录。while中使用ssh时，为了禁止ssh读取行内容后增加一个 “< /dev.null”，会将ssh的输入进行重定向。 While循环块中使用 sed 命令也有此种现象。

解决示例参考：

[root@localhost centos7-00]#

[root@localhost centos7-00]# cat test.sh

cat /etc/hosts | while read hang

server=`echo ${hang} | awk -F " " '{print $1}'`

name=`echo ${hang} | awk -F " " '{print $2}'`

ssh -n root@${server} "ip a"

done

[root@localhost centos7-00]#

[root@localhost centos7-00]# sh -x test.sh

+ cat /etc/hosts

+ read hang

++ echo 192.168.136.145 slave0

++ awk -F ' ' '{print $1}'

+ server=192.168.136.145

++ awk -F ' ' '{print $2}'

++ echo 192.168.136.145 slave0

+ name=slave0

+ ssh -n root@192.168.136.145 'ip a'

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: ens33:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:6d:22:15 brd ff:ff:ff:ff:ff:ff

inet 192.168.136.145/24 brd 192.168.136.255 scope global noprefixroute dynamic ens33

valid_lft 1642sec preferred_lft 1642sec

inet6 fe80::e212:a166:2a5:ffdc/64 scope link noprefixroute

valid_lft forever preferred_lft forever

3: virbr0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

valid_lft forever preferred_lft forever

4: virbr0-nic:  mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

+ read hang

++ echo 192.168.136.152 slave1

++ awk -F ' ' '{print $1}'

+ server=192.168.136.152

++ echo 192.168.136.152 slave1

++ awk -F ' ' '{print $2}'

+ name=slave1

+ ssh -n root@192.168.136.152 'ip a'

1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

valid_lft forever preferred_lft forever

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: ens33:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000

link/ether 00:0c:29:4c:90:50 brd ff:ff:ff:ff:ff:ff

inet 192.168.136.152/24 brd 192.168.136.255 scope global noprefixroute dynamic ens33

valid_lft 1421sec preferred_lft 1421sec

inet6 fe80::e212:a166:2a5:ffdc/64 scope link tentative noprefixroute dadfailed

valid_lft forever preferred_lft forever

inet6 fe80::1018:25e5:682e:fa55/64 scope link noprefixroute

valid_lft forever preferred_lft forever

3: virbr0:  mtu 1500 qdisc noqueue state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

valid_lft forever preferred_lft forever

4: virbr0-nic:  mtu 1500 qdisc pfifo_fast master virbr0 state DOWN group default qlen 1000

link/ether 52:54:00:c8:2c:80 brd ff:ff:ff:ff:ff:ff

+ read hang

[root@localhost centos7-00]#

while循环遍历主机 ssh 主机

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添加新评论1 条评论

热心冰块项目经理浪潮INSPUR
2023-09-15 15:50

大哥，你这牛啊，当初我就是看这Shell的语法复杂及代码太难读才转投了Python。抱歉我没看到10行就直接翻页到底了发评论了。

ubl007： @热心冰块谬赞了，只是在执行命令式出错了，扒拉了扒拉官方文档的解释，给记录了下来

2023-09-16 13:33

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通过 while循环体对远程主机进行遍历性ssh登录并执行目标指令

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