实例1-1 取出网卡的ip地址

方法1

[root@oldboyedu50-lnb /oldboy]# ip a s eth0 |awk 'NR==3'|awk  -F"[ /]+"  '{print $3}'

10.0.0.200

 [root@oldboyedu50-lnb ~]# ifconfig eth0 |awk 'NR==2{}'

[root@oldboyedu50-lnb ~]# ifconfig eth0 |awk 'NR==2{print $2}'

addr:10.0.0.200

方法2

[root@oldboyedu50-lnb ~]# ifconfig eth0 |awk -F'[: ]+' 'NR==2{print $4}'

10.0.0.200

[root@oldboyedu50-lnb ~]# ifconfig eth0

eth0      Link encap:Ethernet  HWaddr 00:0C:29:59:D4:13 

          inet addr:10.0.0.200  Bcast:10.0.0.255  Mask:255.255.255.0

          inet6 addr: fe80::20c:29ff:fe59:d413/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:52080 errors:0 dropped:0 overruns:0 frame:0

          TX packets:25292 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:61200096 (58.3 MiB)  TX bytes:11691848 (11.1 MiB)

方法3

1>定位

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p

2>把ip地址之前的内容替换掉

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p |sed 's#^.*t ##g'

10.0.0.200/24 brd 10.0.0.255 scope global eth0

3>把ip地址之后的替换掉

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p |sed 's#^.*t ##g'|sed 's#/.*$##g'

10.0.0.200

命令优化

使用2个sed

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p |sed -r 's#^.*t |/.*$##g'

10.0.0.200

方法4 sed 后向引用

在前面先保护(你想要的内容),在后面通过\数字使用

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p

    inet 10.0.0.200/24 brd 10.0.0.255 scope global eth0

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p |sed -r 's#^.*t (.*)/.*$#\1#g'

10.0.0.200

实例1-2 ip a s eth0第三行的inet替换为oldboy

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p

    inet 10.0.0.200/24 brd 10.0.0.255 scope global eth0

[root@oldboyedu50-lnb ~]# ip a s eth0 |sed -n 3p|sed 's#inet#oldboy#g'

    oldboy 10.0.0.200/24 brd 10.0.0.255 scope global eth0

实例1-3 只通过正则表达式取出ip

[root@oldboyedu50-lnb ~]# ip a s eth0 |egrep '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'

    inet 10.0.0.200/24 brd 10.0.0.255 scope global eth0

[root@oldboyedu50-lnb ~]# ip a s eth0 |egrep '([0-9]{1,3}\.){3}[0-9]{1,3}'

    inet 10.0.0.200/24 brd 10.0.0.255 scope global eth0

[root@oldboyedu50-lnb ~]# ip a s eth0 |egrep '([0-9]{1,3}\.?){4}'

2: eth0: mtu 1500 qdisc pfifo_fast state UP qlen 1000

    inet 10.0.0.200/24 brd 10.0.0.255 scope global eth0

所有网卡的ip地址

[root@oldboyedu50-lnb ~]# hostname -I

10.0.0.200

实例1-4 取出stat /etc/hosts 文件权限 644 或 0644 

方法1

awk

[root@oldboyedu50-lnb ~]# stat /etc/hosts |awk 'NR==4'

Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)

[root@oldboyedu50-lnb ~]# stat /etc/hosts |awk 'NR==4'|awk -F'[(/]'   '{print $2}'

0644

[root@oldboyedu50-lnb ~]# stat /etc/hosts |awk -F'[(/]'   'NR==4{print $2}'

0644

方法2

sed 后向引用

[root@oldboyedu50-lnb ~]# stat /etc/hosts |sed -n 4p |sed -r 's#(^.*\()([0-9]+)(/.*$)#\1#g'

Access: (

[root@oldboyedu50-lnb ~]# stat /etc/hosts |sed -n 4p |sed -r 's#(^.*\()([0-9]+)(/.*$)#\2#g'

0644

[root@oldboyedu50-lnb ~]# stat /etc/hosts |sed -n 4p |sed -r 's#^.*\(([0-9]+)/.*$#\1#g'

0644

[root@oldboyedu50-lnb ~]#

方法3

[root@oldboyedu50-lnb ~]# stat -c%a  /etc/hosts

644

实例1-5 已知/oldboy/test.txt文件内容为：

oldboy

 

xizi

 

xiaochao

请问如何把文件中的空行过滤掉（要求命令行实现）。

通过三剑客进行过滤

方法1grep

[root@oldboyedu50-lnb /oldboy]# grep -v '^$' test.txt

oldboy

xizi

xiaochao

方法2sed

[root@oldboyedu50-lnb /oldboy]# sed '/^$/d' test.txt

oldboy

xizi

xiaochao

方法3awk

[root@oldboyedu50-lnb /oldboy]# awk '!/^$/' test.txt

oldboy

xizi

xiaochao

实例1-6           已知/oldboy/ett.txt文件内容为：

oldboy

olldboooy

test

请使用grep或egrep正则匹配的方式过滤出前两行内容

方法1 egrep

[root@oldboyedu50-lnb /oldboy]# egrep 'ol+dbo+y' ett.txt

oldboy

olldboooy

方法2sed

[root@oldboyedu50-lnb /oldboy]# sed -nr '/ol+dbo+y/p'  ett.txt

oldboy

olldboooy

方法3awk

[root@oldboyedu50-lnb /oldboy]# awk '/ol+dbo+y/' ett.txt

oldboy

olldboooy

实例1-7           linux下通过mkdir命令创建新目录/oldboy/ett，ett的硬链接数是多少，为什么？

[root@oldboyedu50-lnb /oldboy]# mkdir -p /oldboy/ett

[root@oldboyedu50-lnb /oldboy]# ll -d ett

drwxr-xr-x 2 root root 4096 Jul 20 02:01 ett

[root@oldboyedu50-lnb /oldboy]# ll -di ett ett/.

1046554 drwxr-xr-x 2 root root 4096 Jul 20 02:01 ett

1046554 drwxr-xr-x 2 root root 4096 Jul 20 02:01 ett/.

mkdir -p /oldboy/ett/oldboy

ett目录的硬连接数是？

[root@oldboyedu50-lnb /oldboy]# ll -d ett

drwxr-xr-x 3 root root 4096 Jul 20 02:05 ett

[root@oldboyedu50-lnb /oldboy]# ll -di ett ett/. ett/oldboy/..

1046554 drwxr-xr-x 3 root root 4096 Jul 20 02:05 ett

1046554 drwxr-xr-x 3 root root 4096 Jul 20 02:05 ett/.

1046554 drwxr-xr-x 3 root root 4096 Jul 20 02:05 ett/oldboy/..

实例1-8 按照要求的格式显示日期

[root@oldboyedu50-lnb /oldboy]# date +%F

2018-07-20

[root@oldboyedu50-lnb /oldboy]# date +%Y-%m-%d

2018-07-20

[root@oldboyedu50-lnb /oldboy]# date +%T

02:29:22

[root@oldboyedu50-lnb /oldboy]# date +%H:%M:%S

02:29:46

[root@oldboyedu50-lnb /oldboy]# date +%w

5

小结：

%F  %Y-%m-%d    年-月-日

%T  %H:%M:%S    时:分:秒

%w              周几

实例1-9 显示当前日期格式: 年月日_小时

[root@oldboyedu50-lnb /oldboy]# date +%F

2018-07-20

[root@oldboyedu50-lnb /oldboy]# date -d "1 day ago"

Thu Jul 19 02:41:01 CST 2018

[root@oldboyedu50-lnb /oldboy]# date -d "1day"

Sat Jul 21 02:41:15 CST 2018

[root@oldboyedu50-lnb /oldboy]# date -d "-1day"

Thu Jul 19 02:41:28 CST 2018

[root@oldboyedu50-lnb /oldboy]# date -d "-1day" +%F

2018-07-19

date 显示系统时间

-d  根据你的描述显示指定日期

-d  '-7day'  7天之前

-d  '7day'  7天之后

-d '+7day'  7天之后