Substitution on range of lines

Question

I have in 3rd line of a file. I want to replace that with my_dB. How to do this with sed

Answer 1

Like this:

$ sed '3,6 s//my_dB/' file

Demo:

$ cat file
1: 
2: 
3: 
4: 
5: 
6: 
7: 

$ sed '3,6 s//my_dB/' file
1: 
2: 
3: my_dB
4: my_dB
5: my_dB
6: my_dB

    7:

To store the changes back to the file use the -i option

$ sed -i '3,6 s//my_bd/' file

However you really should be using a XML parser. Getting into parsing XML with regexp is really a bad idea.