ifconfig eth0 | sed -n ‘2p‘| awk  ‘{print $2}‘ | awk -F: ‘{print $2}‘
ifconfig eth0 | grep "inet addr" | cut -d: -f2 | cut -d" " -f1
ifconfig eth0 | sed -n ‘2p‘| awk  -F "[: ]+"  ‘{print $4}‘   #  +重复前面多个分隔符    [空格，冒号为分隔符]
ifconfig eth0 | awk -F "[: ]+" ‘NR==2 {print $4}‘  


[root@augustyang 123]# sed ‘s#\(ddd\) \(kkk\)##g‘ test.txt     

[root@augustyang 123]# sed ‘s#\(ddd\) \(kkk\)#\1#g‘ test.txt
ddd
[root@augustyang 123]# sed ‘s#\(ddd\) \(kkk\)#\1 \2#g‘ test.txt
ddd kkk

[root@augustyang 123]# stat /etc | sed -n ‘4p‘| awk -F"[(/]"  ‘{print $2}‘
0755
[root@augustyang 123]# stat /etc | awk -F "[(/]"  ‘ NR ==4 {print $2}‘
0755

正则表达式练习