How to replace a whole line with sed?

Question

Suppose I have a file with lines

aaa=bbb

Now I would like to replace them with:

aaa=xxx

I can do that as follows:

sed \"s         


        

Answer 1

Like this:

sed 's/aaa=.*/aaa=xxx/'

If you want to guarantee that the aaa= is at the start of the line, make it:

sed 's/^aaa=.*/aaa=xxx/'