grep实例学习

 grep （global search regular expression(RE) and print out the line,全面搜索正则表达式并把行打印出来）是一种强大的文本搜索工具，它能使用正则表达式搜索文本，并把匹配的行打印出来
1、输出真实的（不包含注释#信息）配置项 
-v ，Invert  the  sense  of  matching, to select non-matching lines.显示不包含匹配文本的所有行
-E Interpret  PATTERN  as  an  extended  regular expression，使用扩展正则表达式
^，基本正则表达式，行首定位符
$，基本正则表达式，行尾定位符
^$，空行
|，扩展正则表达式，或
行首定位符

# 查看/etc/sysconfig/selinux全部内容
[root@oracle /]# cat /etc/sysconfig/selinux
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.

SELINUX=disabled

# SELINUXTYPE= can take one of these two values:
#     targeted - Targeted processes are protected,
#     mls - Multi Level Security protection.

SELINUXTYPE=targeted
# 查看不包含注释行的/etc/sysconfig/selinux
[root@oracle /]# cat /etc/sysconfig/selinux | grep -v '^#'

SELINUX=disabled

SELINUXTYPE=targeted

2、匹配IP、MAC地址1、匹配IP、MAC地址
-o Print only the matched (non-empty) parts of  a  matching line, with each such part on a separate output line，只输出匹配字符串
{m,n}，扩展正则表达式，m到n次匹配

[root@oracle ~]# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:0C:29:50:CB:D9
inet addr:192.168.17.202  Bcast:192.168.17.255  Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe50:cbd9/64 Scope:Link
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
RX packets:258 errors:0 dropped:0 overruns:0 frame:0
TX packets:199 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:24411 (23.8 KiB)  TX bytes:24063 (23.4 KiB)
Interrupt:19 Base address:0x2000
[root@oracle ~]# ifconfig |grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}'
192.168.17.202
192.168.17.255
[root@oracle ~]# ifconfig eth0 | grep -oE '([0-9a-zA-Z]{1,2}:){5}[0-9a-zA-Z]{1,2}'
00:0C:29:50:CB:D9