系统符号二——正则表达式及三剑客之grep

---

一基础正则表达式

（一）^  匹配以什么开头的信息

[root@centos71 ~]# grep  "^root"  /etc/passwd
root:x:0:0:root:/root:/bin/bash
[root@centos71 ~]# grep  "^r"  /etc/passwd
root:x:0:0:root:/root:/bin/bash

注意红色显示的才是真正匹配的内容

（二）$——匹配以什么结尾的信息

[root@centos71 ~]# cat  /etc/selinux/config

# 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 three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

[root@centos71 ~]# grep  "disabled$"   /etc/selinux/config
SELINUX=disabled
[root@centos71 ~]# grep  "ed$"   /etc/selinux/config
SELINUX=disabled
SELINUXTYPE=targeted

^$ 匹配空行信息

[root@centos71 ~]# grep  "^$" /etc/selinux/config




[root@centos71 ~]# grep  "^$" /etc/selinux/config  |  wc
      4       0       4
[root@centos71 ~]# 

利用v进行取反，排除空行显示

[root@centos71 ~]# wc   /etc/selinux/config
 15  81 542 /etc/selinux/config
[root@centos71 ~]# grep  -v  "^$"  /etc/selinux/config   |  wc
     11      81     538

（三）. 点——匹配任意一个字符且只有一个字符

[root@centos71 test]# cat  test.txt
gd
god
good
goood
gooood
[root@centos71 test]# grep   "g.d"  test.txt
god
[root@centos71 test]# grep   "g..d"  test.txt
good
[root@centos71 test]# grep   "g...d"  test.txt
goood
[root@centos71 test]# grep   "g....d"  test.txt
gooood
[root@centos71 test]# grep   "g.....d"  test.txt
[root@centos71 test]# pwd
/test

[root@centos71 test]#  grep   "g.d"  test.txt  -o
god
[root@centos71 test]#  grep   "g..d"  test.txt  -o
good
[root@centos71 test]#  grep   "g...d"  test.txt  -o
goood

贪婪匹配，尽可能多的匹配

[root@centos71 test]# cat  test.txt
gd
god
good
goood
gooood
[root@centos71 test]# grep   ".d"  test.txt
gd
god
good
goood
gooood

（四）* 匹配符号前面一个字符连续出现0次或者多次

[root@centos71 test]# cat  test.txt
gd
god
good
goood
gooood
[root@centos71 test]# grep   "o*"  test.txt
gd
god
good
goood
gooood

匹配任意一个字符连续出现多次，空格也是字符

[root@centos71 ~]# cat  /etc/passwd  |  grep  "^n.*n$"
nobody:x:99:99:Nobody:/:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
nginx:x:997:995:Nginx web server:/var/lib/nginx:/sbin/nologin

（五） .* ——匹配任意所有字符信息

[root@centos71 ~]# cat  /etc/passwd  |  grep  "^n.*n$"
nobody:x:99:99:Nobody:/:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
nginx:x:997:995:Nginx web server:/var/lib/nginx:/sbin/nologin

[root@centos71 ~]# cat  /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
[root@centos71 ~]# cat  /etc/hosts  |  grep  "^[0-9].*[0-9]$"
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

（六）撬棍——转义（将意思进行转变）符号

1) 将有意义信息变得没有意义
2) 将没意义信息变得有意义

表示任意一个字符结尾

[root@centos71 ~]# cat  /etc/selinux/config  |  grep  ".$"
# 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 three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

变成普通的点

[root@centos71 ~]# cat  /etc/selinux/config  |  grep  ".$"
# This file controls the state of SELinux on the system.
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
#     mls - Multi Level Security protection.
[root@centos71 ~]# 

转义符号将没意义信息变得有意义

  --- 制表符号
  --- 换行符号
  --- 换行符号

换行符对于echo来说是高级符号，要加参数e来识别，和颜色一样

[root@centos71 test]# echo  wuwuwuwuhahahaha
wuwuwuwuhahahaha
[root@centos71 test]# echo  wuwuwuwu
hahahaha
wuwuwuwunhahahaha
[root@centos71 test]# echo -e   wuwuwuwu
hahahaha
wuwuwuwunhahahaha
[root@centos71 test]# echo    "wuwuwuwu
hahahaha"
wuwuwuwu
hahahaha
[root@centos71 test]# echo   -e   "wuwuwuwu
hahahaha"
wuwuwuwu
hahahaha

制表符可以保持word文本间距等齐

（七）[  ]——匹配多个字符信息

[root@centos71 ~]# catnet0  |  grep  "[IP]"
TYPE=Ethernet
PROXY_METHOD=none
BOOTPROTO=none
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
UUID=9d9e2656-f3ac-4f75-8722-3136d239985d
DEVICE=eth0
IPADDR=10.0.0.200
PREFIX=24
IPV6_PRIVACY=no

 

[root@centos71 ~]# catnet0  |  grep  "[IP]"  -o
P
P
P
I
P
I
I
P
I
I
I
P
I
P
I
P
I
I
P
I
I
I
P
P
I
I
P
P
I

注意中括号里面不加^，而是加其他字符就会被解释为普通字符

[root@centos71 ~]# grep  -E  "[=]"  /etc/selinux/config
# SELINUX= can take one of these three values:
SELINUX=enforcing
# SELINUXTYPE= can take one of three values:
SELINUXTYPE=targeted
[root@centos71 ~]# grep  -E  "[=]"  /etc/selinux/config  -o
=
=
=
=

但是这样的话直接过滤就可以了

[root@centos71 test]# grep    "="  /etc/selinux/config
# SELINUX= can take one of these three values:
SELINUX=enforcing
# SELINUXTYPE= can take one of three values:
SELINUXTYPE=targeted
[root@centos71 test]# grep    "="  /etc/selinux/config  -o
=
=
=
=

（八）[  ^ ]——匹配多个字符信息进行取反排除

[root@centos71 ~]#  cat  /etc/issue
S
Kernel 
 on an m

[root@centos71 ~]# cat  /etc/issue |  grep    "[^a-z]" 
S
Kernel 
 on an m
[root@centos71 ~]# cat  /etc/issue |  grep    "[^a-z]" -o

S
K
 

 
 
 

二扩展正则表达式

（一）+——匹配符号前面一个字符连续出现1次或者多次

[root@centos71 test]# cat  test.txt
gd
god
good
goood
gooood

[root@centos71 test]# grep  -E   "o+" test.txt
god
good
goood
gooood

注意使用撬棍可以使+进行转义，变成单纯的+

[root@centos71 test]# cat  mul.txt 
t+t+
r+r+r+
w+w+w+w+
x+x+x+x+x+
[root@centos71 test]# grep     "+"   mul.txt  
t+t+
r+r+r+
w+w+w+w+
x+x+x+x+x+
[root@centos71 test]# grep     "+"   mul.txt  -o
+
+
+
+
+
+
+
+
+
+
+
+
+
+

直接过滤更方便

[root@centos71 test]# grep     "+"   mul.txt  
t+t+
r+r+r+
w+w+w+w+
x+x+x+x+x+
[root@centos71 test]# grep     "+"   mul.txt  -o
+
+
+
+
+
+
+
+
+
+
+
+
+
+

.+匹配任意一个字符一次以上

[root@centos71 test]# grep  -E  ".+"  /etc/issue
S
Kernel 
 on an m
[root@centos71 test]# grep  -E  ".+"  /etc/issue  -o
S
Kernel 
 on an m

（二）？——匹配符号前面一个字符连续出现0次或1次

易错点：2，3，4个o包含了1个o

[root@centos71 test]# grep  -E   "o?" test.txt
gd
god
good
goood
gooood

查看过程很明显

[root@centos71 test]# grep  -E   "o?" test.txt  -o
o
o
o
o
o
o
o
o
o
o

（三）{  }——匹配符号前面一个字符连续出现指定次数

匹配o为2-3次

[root@centos71 test]# grep  -E   "o{2,3}" test.txt  
good
goood
gooood

过滤的过程

[root@centos71 test]# grep  -E   "o{2,3}" test.txt  -o
oo
ooo
ooo

匹配o在2次以上

[root@centos71 test]# cat  test.txt 
gd
god
good
goood
gooood
[root@centos71 test]#  grep  -E   "o{2,}" test.txt  
good
goood
gooood
[root@centos71 test]#  grep  -E   "o{2,}" test.txt   -o
oo
ooo
oooo

注意最后一行是3+1，看过程

[root@centos71 test]#  grep  -E   "o{,3}" test.txt   
gd
god
good
goood
gooood
[root@centos71 test]#  grep  -E   "o{,3}" test.txt   -o
o
oo
ooo
ooo
o

-w按照单词进行过滤

注意此单词非彼单词，是以空格作为分割符

[root@centos71 test]# cat     identify.txt  
linda  110109190006078765
merry  105110120110028123
suhadu 12482749277297292731829371
[root@centos71 test]# cat     identify.txt  |  grep  -Ew   "[0-9]{18}"
linda  110109190006078765
merry  105110120110028123

[root@centos71 test]# cat    identif.txt   |  grep  -Ew  "([0-9]|X$){18}"  -o
110109197706078765
105110111100281236
10511011110028123X

（四）|——匹配多个字符串信息

[root@centos71 ~]# grep  -E "~#|^$|#"  /etc/selinux/config

# 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.
# SELINUXTYPE= can take one of three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.



[root@centos71 ~]# grep  -vE "~#|^$|#"  /etc/selinux/config
SELINUX=disabled
SELINUXTYPE=targeted

 匹配以#开头或者以.结尾的行

[root@centos71 ~]# grep  -E    "^#|.$"  /etc/selinux/config
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
# SELINUXTYPE= can take one of three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.
[root@centos71 ~]# grep  -E    "^#|.$"  /etc/selinux/config   -o
#
.
#
#
.
#
.
#
.
#
#
#
#
.

（五）（）——将多个字符信息汇总成一个整体

过滤出含有disabled的行

[root@centos71 ~]# grep  -E   "(disabled)"  /etc/selinux/config 
#     disabled - No SELinux policy is loaded.
SELINUX=disabled
[root@centos71 ~]# grep  -E   "(disabled)"  /etc/selinux/config  -o
disabled
disabled

下面情况是分开的，disabled中的任意一个字符出现即可

[root@centos71 ~]# grep  -E   "([disabled])"  /etc/selinux/config 
# 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 three values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected. 
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted

 

匹配多次出现的单词

注意下面（）和[ ]的区别

[root@centos71 test]# cat  hahaha.txt
hahahahahahahahaha
wuwuwuwuwuwuwuwuwu
xixixixixixixixixi
aiaiaiaiaiaiaiaiai
heiheiheiheiheihei
hehehehehehehehehe
bababababababababa
mamamamamamamamama

表示匹配3次x或者i

[root@centos71 test]# cat  hahaha.txt  |  grep  -E   "[xi]{3}"  
xixixixixixixixixi
[root@centos71 test]# cat  hahaha.txt  |  grep  -E   "[xi]{3}"  -o
xix
ixi
xix
ixi
xix
ixi

匹配3次xi，并且是贪婪匹配

[root@centos71 test]# cat  hahaha.txt  |  grep  -E   "(xi){3}"  
xixixixixixixixixi
[root@centos71 test]# cat  hahaha.txt  |  grep  -E   "(xi){3}"  -o
xixixi
xixixi
xixixi

利用sed进行替换时, 实现后向引用前项

[root@centos71 ~]# echo 123456    | sed   's#123456#<123456>#g'  
<123456>

[root@centos71 ~]# echo   654321    | sed   's#123456#<123456>#g'  
654321

（）表示把字符都保护起来，.*表示前面的任意字符

[root@centos71 ~]# echo   654321    | sed   -r  's#(.*)#<1>#g'  
<654321>

拆分，每2个一组，<>是装饰，2表示前面第2部分

3000=1040多看

[root@centos71 ~]# echo 12345678787878787878  |  sed   -r  's#(..)(..)(..)(..)(..)(..)(..)(..)(..)(..)#<1><2><3><4><5><6><7><8><9><10>#g'
<12><34><56><78><78><78><78><78><78><120>

正确显示，匹配偶数个

[root@centos71 ~]# echo 12345678787878787878  |  sed   -r  's#(.{2})#<1>#g'
<12><34><56><78><78><78><78><78><78><78>

匹配奇数个

[root@centos71 ~]# echo 123456787878787878789  |  sed   -r  's#(.{1,2})#<1>#g'
<12><34><56><78><78><78><78><78><78><78><9>

[root@centos71 ~]# echo 123456787878787878789  |  sed   -r  's#(.{1,2})#{1}#g'
{12}{34}{56}{78}{78}{78}{78}{78}{78}{78}{9}
[root@centos71 ~]# echo 123456787878787878789  |  sed   -r  's#(.{1,2})#{2}#g'
sed: -e expression #1, char 17: invalid reference 2 on `s' command's RHS
[root@centos71 ~]# echo 123456787878787878789  |  sed   -r  's#(.{1,2})#{3}#g'
sed: -e expression #1, char 17: invalid reference 3 on `s' command's RHS

练习一——取出特定文件的权限

先定位，并且要选择独特的关键字

[root@centos71 test]#  stat   /etc/hosts 
  File: ‘/etc/hosts’
  Size: 158           Blocks: 8          IO Block: 4096   regular file
Device: 803h/2051d    Inode: 35530425    Links: 1
Access: (0640/-rw-r-----)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-12-18 11:50:37.597173908 +0800
Modify: 2019-12-16 11:42:41.175934855 +0800
Change: 2019-12-18 11:09:06.359382129 +0800
 Birth: -

[root@centos71 test]#  stat   /etc/hosts | grep Uid 
Access: (0640/-rw-r-----)  Uid: (    0/    root)   Gid: (    0/    root)

[root@centos71 test]# stat   /etc/hosts | grep Uid  |   grep -E   "[0-7]{4}"
Access: (0640/-rw-r-----)  Uid: (    0/    root)   Gid: (    0/    root)

[root@centos71 ~]#  stat   /etc/hosts | grep Uid  |   grep -E   "[0-7]{4}" -o
0640

练习二——取出IP地址信息   

注意如果centos7修改为传统网卡，那么下面方法也适用于centos6

[0-9]表示IP地址的数字

{1，3}表示最少1位，最多3位

后面匹配的是点，而不是任意字符，所以要加上

方法一

显示指定的网卡信息

[root@centos71 ~]# ip a s eth0 
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0c:29:ea:b8:14 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::951a:d6ce:9fbd:c7b7/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

注意关键字后面是有空格的，这样和inet6那么区分开

[root@centos71 ~]# ip a s eth0|grep "inet "
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0

匹配到了IP地址的网络位，也就是xxx.xxx.xxx.格式

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "(([0-9]{1,3}.){3}[0-9]{1,3})"  
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0
[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "(([0-9]{1,3}.){3}[0-9]{1,3})"  -o
10.0.0.200
10.0.0.255

已经完全匹配了IP地址，但是要把广播地址过滤掉

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "(([0-9]{1,3}.){3}[0-9]{1,3})"
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0
[root@centos71 ~]# 

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "(([0-9]{1,3}.){3}[0-9]{1,3})"  -o
10.0.0.200
10.0.0.255

通过特征过滤掉另外一个地址

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "(([0-9]{1,3}.){3}[0-9]{1,3})"  -o | head  -1
10.0.0.200

方法二

.?组合符号，表示匹配.（点）的次数为0-1次

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9]{1,3}.?){4}" 
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0
[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9]{1,3}.?){4}" -o 
10.0.0.200
10.0.0.255
[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9]{1,3}.?){4}" -o  |  head  -1
10.0.0.200

方法三

把数字和点组合起来，要么是数字要么是点，点为固定数3个

最少是3个点+4个数字，此时数字为一位数；最多是3个点+12个数字，此时数字为三位数

[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  
    inet 10.0.0.200/24 brd 10.0.0.255 scope global noprefixroute eth0
[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  -o 
10.0.0.200
10.0.0.255
[root@centos71 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  -o | head  -1
10.0.0.200

注意IPV6的地址有8组

xxxx:xxxx:xxxx：0000：0000：0000：：xxxx:xxxx

centos6

[root@centos61 ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:bc:ff:d7 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.61/24 brd 10.0.0.255 scope global eth0
    inet6 fe80::20c:29ff:febc:ffd7/64 scope link 
       valid_lft forever preferred_lft forever
[root@centos61 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  
    inet 10.0.0.61/24 brd 10.0.0.255 scope global eth0
[root@centos61 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  -o
10.0.0.61
10.0.0.255
[root@centos61 ~]# ip a s eth0|grep "inet "|grep -E "([0-9.]{7,15})"  -o |  head  -1
10.0.0.61

练习三——磁盘使用率

[root@centos71 ~]# df  -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        40G  3.0G   38G   8% /
devtmpfs        476M     0  476M   0% /dev
tmpfs           487M     0  487M   0% /dev/shm
tmpfs           487M  7.7M  479M   2% /run
tmpfs           487M     0  487M   0% /sys/fs/cgroup
/dev/sda1       197M  105M   93M  54% /boot
tmpfs            98M     0   98M   0% /run/user/0
[root@centos71 ~]# df -h | grep /dev/sda1|grep -E "[0-9]{1,3}%" 
/dev/sda1       197M  105M   93M  54% /boot
[root@centos71 ~]# df -h | grep /dev/sda1|grep -E "[0-9]{1,3}%"  -o
54%

一般两位数就可以了，%可以进行区分

说明：正则匹配一行信息时，默认有贪婪特性

[root@centos71 ~]# df -h | grep /dev/sda1|grep -E "[0-9]{1,2}%"  -o
54%

三grep常用参数总结

grep -i   --- 忽略大小写搜索信息

  -i, --ignore-case
              Ignore case distinctions in both the PATTERN and the input files.  (-i is specified  by
              POSIX.)

grep -n   --- 搜索信息后显示行号

 -n, --line-number
              Prefix  each line of output with the 1-based line number within its input file.  (-n is
              specified by POSIX.)

grep -c   --- 统计筛选出来的行数

  -c, --count
              Suppress  normal  output;  instead print a count of matching lines for each input file.
              With the -v, --invert-match option (see  below),  count  non-matching  lines.   (-c  is
              specified by POSIX.)

grep -v   --- 将搜索信息进行取反

 -v, --invert-match
              Invert  the  sense  of  matching,  to  select  non-matching lines.  (-v is specified by
              POSIX.)

grep -w   --- 按照字符串进行匹配

  -w, --word-regexp
              Select only those lines containing matches that form whole words.  The test is that the
              matching  substring  must either be at the beginning of the line, or preceded by a non-
              word constituent character.  Similarly, it must be either at the end  of  the  line  or
              followed by a non-word constituent character.  Word-constituent characters are letters,
              digits, and the underscore.

[root@centos71 test]# cat  test3.txt
abc abcd abcde abcdef

grep -o   --- 只输出显示匹配信息

  -o, --only-matching
              Print only the matched (non-empty) parts of a matching line, with each such part  on  a
              separate output line.

grep -A   --- 过滤指定内容之后的信息

  -A NUM, --after-context=NUM
              Print  NUM  lines of trailing context after matching lines.  Places a line containing a
              group separator  (described  under  --group-separator)  between  contiguous  groups  of
              matches.   With  the  -o or --only-matching option, this has no effect and a warning is
              given.

grep -B   --- 过滤指定内容之前的信息

 -B NUM, --before-context=NUM
              Print NUM lines of leading context before matching lines.  Places a line  containing  a
              group  separator  (described  under  --group-separator)  between  contiguous  groups of
              matches.  With the -o or --only-matching option, this has no effect and  a  warning  is
              given.

grep -C   --- 过滤指定内容上下几行的信息  

  -C NUM, -NUM, --context=NUM
              Print  NUM  lines  of  output  context.   Places  a  line  containing a group separator
              (described under --group-separator) between contiguous groups of matches.  With the  -o
              or --only-matching option, this has no effect and a warning is given.

grep -E   --- 识别扩展正则信息

   -E, --extended-regexp
              Interpret PATTERN as an extended regular expression (ERE, see below).  (-E is specified
              by POSIX.)

grep -r   --- 递归搜索指定数据信息

  -r, --recursive
              Read all files under each directory, recursively, following symbolic links only if they
              are on the command line.  This is equivalent to the -d recurse option.

[root@centos71 test]# mkdir  /test/test1/test2   -p
[root@centos71 test]# vim  /test/test1/test2/test2.txt
hahahahaha

[root@centos71 test]# grep  -r   "hahaha"   
hahaha.txt:hahahahahahahahaha
test1/test2/test2.txt:hahahahaha
[root@centos71 test]# tree  
.
├── aaa.txt
├── aa.txt
├── aa.txt_hard_link
├── hahaha.txt
├── identif.txt
├── identify.txt
├── mail.txt
├── m.conf.tar.gz
├── m.tar.gz
├── qq_num.txt
├── test1
│   └── test2
│       └── test2.txt
├── test2.txt
├── test3.txt
└── test.txt

2 directories, 14 files