Remote bulk file edits and administration with SSH and SED ( sed examples )

Want to deploy the zabbix agent to a bunch of Ubuntu Linux systems? Easy. But wait... the config file for each needs to be updated. How about this:
for target in host1 host2 host3 host4; do echo $target; ssh -t $target "apt-get -y install zabbix-agent; sed -i.bak -e \"s/Server=localhost/Server=\" -e \"s/Hostname=localhost/Hostname=$target/g\" /etc/zabbix/zabbix_agent.conf /etc/zabbix/zabbix_agentd.conf; update-rc.d zabbix-agent enable; /etc/init.d/zabbix-agent restart"; done

This will:
  1. ssh to each host
  2. install the agent on that host
  3. replace the default "Server=" and the "Hostname=" lines in the two config files zabbix_agent.conf and zabbix_agentd.conf", where is the zabbix server ip address.
  4. make a backup of the two config files
  5. configure the zabbix_agent to auto-start
  6. restart the zabbix agent to pick up the config file changes.
That was easier and more reliable than trying to complete the procedure on 50 systems.
(think about updating fstab and others for a mass of hosts.)

For a simple file in-place edit of one line of a file (such as to comment out a line on all the systems' config files):
for target in host1 host2 host3 host4; do echo $target; ssh $target "sed -i.bak -e 's/^domain mynisdomain server mynismaster.company.com$/g #domain mynisdomain server mynismaster.company.com' /etc/yp.conf"; done
If you have a file to edit, and the line you want to replace has quote marks, you'll need to escape them with \\\ like so:
for target in host1 host2 host3 host4; do ssh $target "sed -i.bak -e \"s/^ENABLED=\\\"false\\\"/ENABLED=\\\"true\\\"/g\" /etc/default/sysstat "; done

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