select a certain line from file

hi again!

I'm writing a bash script and I wonder how can I select a certain line from a file.For example I only want the line that starts with
a specific word(given that there's only one starting with this word)
and then by using sed perform an operation to this certain line

Code:

---

Residence: info info2 info2

---

So I want the line that starts with Residence: and then do something with sed to this line

Given that sed will find the line for you as well, what's the point of using something else?

sed '/pattern/x' file

pattern is what you want to look for
x is what you want to do