I'm new in Unix, and I'm learning about sed command. I need to write a very small script for searching a number in a file and replacing it. I tried doing grep, and than deleting the specific phone number from a file, and then adding another one. But i was told that i can use sed in a script to replace. I know how to use the sed command on a command line for search, and replacing something. But how do i write a script, which lets the user search a number, and then let the user enter the number which they want to replace the old number with. So far what i did was use grep to find a number, that works. but now I'm stuck at how can i let the user add in the new number, so the new number can replace the old one. I tried piping grep to sed, and vice versa. No luck so far. I sound redundant, :/ but I'm really frustrated. Any help will be appreciated :D. 
How do i create a sed script to prompt the user to replace a number in a file?
sed;awk;scripting;grep;replace