Enough sed - insert and append

Let’s take a look at our test.txt file with the following content:

sad
happy
awake
coffee
work
school

If we want to insert the word breakfast before coffee, we would do the following:

$ sed '/coffee/i breakfast' test.txt
sad
happy
awake
breakfast
coffee
work
school
$

We can also append the word breakfast after coffee with the following:

$ sed '/coffee/a breakfast' test.txt
sad
happy
awake
coffee
breakfast
work
school
$

Note that this does not change the original test.txt file.