① 定义
grep是行级设备，它分析一行信息，若当中有我们所需要的信息，就将整行返回
② 作用
进行字符串数据的对比，将符合用户需求的字符串打印出来
③ 格式
grep [-acinv] [--color=auto] '查找字符串' filename
参数：
-a：将二进制文件一text文件的方式查找数据
-c：计算找到‘查找字符串’的次数
-i：对大小写透明
-n：输出行号
-v：显示没有‘查找字符串’内容的那一行
-A:后面可加数字，为after的意思，除了列出该行外，后续的n行也列出来
-B:后面可加数字，为before的意思，除了列出该行外，前面的n行也列出来
--color=auto：关键字上色
④ 例子
eg01：找出有检查点事件发生的标志
[Oracle@localhost bdump]$ grep -in --color=auto 'checkpoint' alert_orcl.log
64: checkpoint is 446074
66: checkpoint is 446074
69: checkpoint is 446074
72: checkpoint is 446074
383: checkpoint is 460200
1845:Checkpoint not complete
2112: checkpoint is 606217
2114: checkpoint is 606217
2116: checkpoint is 606217
2118: checkpoint is 606217
2120: checkpoint is 606217
eg02：从内核中找出网卡相关信息
[oracle@localhost bdump]$ dmesg | grep -n -A3 -B2 --color=auto 'eth'
599-iscsi: registered transport (iser)
600-iscsi: registered transport (be2iscsi)
601:eth0: no IPv6 routers present
602-Bluetooth: Core ver 2.10
603-NET: Registered protocol family 31
604-Bluetooth: HCI device and connection manager initialized
--
615-ip_conntrack version 2.4 (8192 buckets, 65536 max) - 228 bytes per conntrack
616-ip6_tables: (C) 2000-2006 Netfilter Core Team
617:peth0: Promiscuous mode enabled.
618:device peth0 entered promiscuous mode
619:xenbr0: port 1(peth0) entering forwarding state
620-device vif0.0 entered promiscuous mode
621-New device vif0.0 does not support netpoll
622-Disabling netpoll for xenbr0
--
625-hdc: drive_cmd: error=0x04 { AbortedCommand }
626-ide: failed opcode was: 0xec
627:eth0: no IPv6 routers present
628:xenbr0: port 1(peth0) entering disabled state
629:xenbr0: port 1(peth0) entering forwarding state