Linux 命令之 grep

1:将/etc/passwd中有root字符的行显示出来

 [root@bogon zkero]# grep -n 'root' /etc/passwd
 :root:x:::root:/root:/bin/bash
 :operator:x:::operator:/root:/sbin/nologin

2:指定文件（test1）中读取hello 无论大小写的行

 [root@bogon zkero]# grep -in 'hello' test1
 :hello
 :HELLO

说明：grep 中‘hello’中的'hello'大小写也是忽略的

3：定位符的使用^

/etc/passwd 中只显示首次出现root的行

 [root@bogon zkero]# grep -n 'root' /etc/passwd
 :root:x:::root:/root:/bin/bash
 :operator:x:::operator:/root:/sbin/nologin
 [root@bogon zkero]# grep -n '^root' /etc/passwd
 :root:x:::root:/root:/bin/bash

^在[ ]之内是反向选择，在[ ]之外是定位符

4：显示行尾字符所在行

 [root@bogon zkero]# grep -n 'bash$' /etc/passwd
 :root:x:::root:/root:/bin/bash
 :zkero:x:::zkero:/home/zkero:/bin/bash

5：定位显示空白行

 [root@bogon zkero]# cat -n test1
          hello
          world
          HELLO

          WORLD

          i an supker
          i like computer!

 [root@bogon zkero]# grep -n '^$' test1
 :
 :
 :

6：一般脚本文件都有空白行和#注释开头的行，如果特殊需要，需要省略这些行：

 [root@bogon zkero]# cat /etc/sysctl.conf
 # Kernel sysctl configuration file for Red Hat Linux
 #
 # For binary values,  is disabled,  is enabled.  See sysctl() and
 # sysctl.conf() for more details.

 # Controls IP packet forwarding
 net.ipv4.ip_forward = 

 # Controls source route verification
 net.ipv4.conf.default.rp_filter = 

 # Do not accept source routing
 net.ipv4.conf.default.accept_source_route = 

 # Controls the System Request debugging functionality of the kernel
 kernel.sysrq = 

 # Controls whether core dumps will append the PID to the core filename.
 # Useful for debugging multi-threaded applications.
 kernel.core_uses_pid = 

 # Controls the use of TCP syncookies
 net.ipv4.tcp_syncookies = 

 # Disable netfilter on bridges.
 net.bridge.bridge-nf-call-ip6tables =
 net.bridge.bridge-nf-call-iptables =
 net.bridge.bridge-nf-call-arptables = 

 # Controls the default maxmimum size of a mesage queue
 kernel.msgmnb = 

 # Controls the maximum size of a message, in bytes
 kernel.msgmax = 

 # Controls the maximum shared segment size, in bytes
 kernel.shmmax = 

 # Controls the maximum number of shared memory segments, in pages
 kernel.shmall =
 [root@bogon zkero]# grep -v '^$' /etc/sysc
 sysconfig/   sysctl.conf
 [root@bogon zkero]# grep -v '^$' /etc/sysctl.conf | grep -v '^#'
 net.ipv4.ip_forward =
 net.ipv4.conf.default.rp_filter =
 net.ipv4.conf.default.accept_source_route =
 kernel.sysrq =
 kernel.core_uses_pid =
 net.ipv4.tcp_syncookies =
 net.bridge.bridge-nf-call-ip6tables =
 net.bridge.bridge-nf-call-iptables =
 net.bridge.bridge-nf-call-arptables =
 kernel.msgmnb =
 kernel.msgmax =
 kernel.shmmax =
 kernel.shmall = 

7: 限定连续RE字符范围{ } 

找两个连续的o字符

 [zkero@bogon ~]$ cat test2
 mygod!
 good morning!
 eat food!
 gooooodbye!

 [zkero@bogon ~]$ grep -n 'o\{2\}' test2
 :good morning!
 :eat food!
 :gooooodbye!

其中：{ } 为特殊符号，需要用\转义

查找连续字符后面接特定字符：比如：3到5个连续字符o后面接d

 [zkero@bogon ~]$ grep -n 'o\{3,5\}d' test2
 :gooooodbye!

查找g开头，d结尾，指定o数目的例子：

 [zkero@bogon ~]$ grep -n 'go\{2,5\}d' test2
 :good morning!
 :gooooodbye!
 [zkero@bogon ~]$ grep -n 'go\{2,4\}d' test2
 :good morning!

可知：第4行有5个o,指定2到4个范围，并没有出现第4行内容