今天在经过多次执行脚本后时候突然发现：/etc/hosts下面有好多重复的行，突然想起来之前记得学过有命令的，但是忘了，后来在群里面吼了几句，有好多牛人相应，闲来与大家分享，O(∩_∩)O~
[root@zy zy]# cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost puppet
192.168.55.229 master.puppet.com master
192.168.55.230 node1.puppet.com node1
192.168.55.231 node2.puppet.com node2
192.168.55.81 puppetmaster.99bill.com
192.168.55.229 zy.99bill.com zy
192.168.55.229 zy.99bill.com zy
192.168.55.229 zy.99bill.com zy
# cat /etc/hosts | sort | uniq
[root@zy zy]# cat /etc/hosts | sort | uniq
127.0.0.1 localhost.localdomain localhost puppet
192.168.55.229 master.puppet.com master
192.168.55.229 zy.99bill.com zy
192.168.55.230 node1.puppet.com node1
192.168.55.231 node2.puppet.com node2
192.168.55.81 puppetmaster.99bill.com
# Do not remove the following line, or various programs
# that require network functionality will fail.
注意查看：顺序发生了变化，这是因为sort的原因。
那么我们可以直接执行：
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost puppet
192.168.55.229 master.puppet.com master
192.168.55.230 node1.puppet.com node1
192.168.55.231 node2.puppet.com node2
192.168.55.81 puppetmaster.99bill.com
192.168.55.229 zy.99bill.com zy
注意：这次我们发现只是重复的行给删除了，只保留了一行。
另外：
# cat /etc/hosts | sort -u
可以直接删除重复的,嘿嘿。。。