SED command application

SED command:
echo "I am oldboy,my QQ is 1234567" >>oldboy.txt
Requirements:
1. Remove the Oldboy string from the Oldboy.txt file
Method One:
[Email protected] oldboy]# echo "I am oldboy,my QQ is 1234567" >oldboy.txt
[email protected] oldboy]# cat Oldboy.txt
I am oldboy,my QQ is 1234567
[[Email protected] oldboy]# sed ' s#^.*m # #g ' Oldboy.txt
Oldboy,my QQ is 1234567
[[Email protected] oldboy]# sed ' s#^.*m # #g ' oldboy.txt |sed ' s#,.*# #g '
Oldboy
[[Email protected] oldboy]# sed ' s/^.*m//g ' oldboy.txt|sed ' s/,.*//g '
Oldboy
Note: "#" and "/" are both symbols of substitution
Method Two:
[[Email protected] oldboy]# sed ' s#^.*m \ (oldboy\),. *#\1#g ' Oldboy.txt
Oldboy

[[email protected] oldboy]# sed ' s#^.*m \ (old\) \ (boy\),. *#\1#g ' oldboy.txt
Old
[[email protected ] oldboy]# sed ' s#^.*m \ (old\) \ (boy\),. *#\1\2#g ' oldboy.txt
Oldboy
[[email protected] oldboy]# sed ' s#^.*m \ (old\) \ (boy\),. *#\2#g ' oldboy.txt
Boy
\ followed by a number means to take out the contents of the front parenthesis, the first parenthesis represents 1, the second represents 2, and so on.

Requirements:
[email protected] oldboy]# cat Oldboy.txt
I am oldboy,my QQ is 1234567
I am old,but am Strong
Welcome to test
Remove rows containing old without Oldboy in Oldboy.txt
Method One:
[[Email protected] oldboy]# sed '/old[^boy]/d ' oldboy.txt
I am oldboy,my QQ is 1234567
Welcome to test
Method Two:
[[Email protected] oldboy]# sed '/\<old\>/d ' oldboy.txt
I am oldboy,my QQ is 1234567
Welcome to test
"<>" matches a single character
Replace a row with old without a boy with www.baidu.com
[Email protected] oldboy]# sed ' s#old[^boy] #www. Baidu.com#g ' Oldboy.txt
I am oldboy,my QQ is 1234567
I am www.baidu.combut am Strong
Welcome to test
[Email protected] oldboy]# sed ' s#\<old\> #www. Baidu.com#g ' Oldboy.txt
I am oldboy,my QQ is 1234567
I am www.baidu.com,but am Strong
Welcome to test

SED command application