匹配以非数字的行，也就是取反，除了数字外其他的都是显示红色
[root@kylin sam]# grep ‘[^0-9]‘ inittab

inittab is only used by upstart for the default runlevel.

#

ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.

#

System initialization is started by /etc/init/rcS.conf

在[]前面再^显示以非数字开头的行
[root@kylin sam]# grep ‘^[^0-9]‘ inittab

inittab is only used by upstart for the default runlevel.

#

ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.

#

System initialization is started by /etc/init/rcS.conf

#

. 可以匹配以r开头o结尾的中间匹配一个字符
[root@kylin sam]# grep ‘r.o‘ passwd
root:x:0:0:root:/root:/bin/bash
2323r&o
operator:x:11:0:operator:/root:/sbin/nologin

前面这个o可以匹配多次，
[root@kylin sam]# grep ‘oo‘ passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin

. 匹配所有的字符
[root@kylin sam]# grep ‘.‘ passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
ROOT
daemon:x:2:2:daemon:/sbin:/sbin/nologin
sdffsdr00o12
2323r&o
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown

o {} 是匹配的一个范围， 可以匹配两次，有两个斜杠是脱意的用法
[root@kylin sam]# grep ‘o{2}‘ passwd
root:x:0:0:root:/root:/bin/bash
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin
postfix:x:89:89::/var/spoool/postfix:/sbin/nologin

grep -E =egrep 用-E就可以省去脱意的/
[root@kylin sam]# grep -E ‘o{2}‘ passwd
root:x:0:0:root:/root:/bin/bash
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin
postfix:x:89:89::/var/spoool/postfix:/sbin/nologin
[root@kylin sam]# egrep ‘o{2}‘ passwd
root:x:0:0:root:/root:/bin/bash
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin
postfix:x:89:89::/var/spoool/postfix:/sbin/nologin

用()括起来表示一个整体匹配有两个oo的
[root@kylin sam]# grep -E ‘(oo){2}‘ passwd
vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin

• +前面的这个字符匹配一次或多次
  [root@kylin sam]# grep -E ‘o+o‘ passwd
  root:x:0:0:root:/root:/bin/bash
  lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
  mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
  uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
  operator:x:11:0:operator:/root:/sbin/nologin
  vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin
  postfix:x:89:89::/var/spoool/postfix:/sbin/nologin

也可以匹配其他的字符
[root@kylin sam]# grep -E ‘o+b‘ passwd
nobody:x:99:99:Nobody:/:/sbin/nologin

？ ？前面的这个字符重复0次或者1次
[root@kylin sam]# grep -E ‘o?t‘ passwd
root:x:0:0:root:/root:/bin/bash
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
operator:x:11:0:operator:/root:/sbin/nologin
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
dbus:x:81:81:System message bus:/:/sbin/nologin
vcsa:x:69:69:virtual console memory oooowner:/dev:/sbin/nologin
saslauth:x:499:76:"Saslauthd user":/var/empty/saslauth:/sbin/nologin
postfix:x:89:89::/var/spoool/postfix:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin

| 或者，匹配root或者nobody
[root@kylin sam]# grep -E ‘root|nobody‘ passwd
root:x:0:0:root:/root:/bin/bash
operator:x:11:0:operator:/root:/sbin/nologin
nobody:x:99:99:Nobody:/:/sbin/nologin