Raw Input		Desired Output
cats meow in the meadow dogs bark in the yard pigs sleep in the garden I have a cat and a dog birds fly in the blue sky		I have a cat and a dog

Script and Comments

Script₁

[ 1] /PAT/h
[ 2] $!d
[ 3] x

Comments

'Pattern space' and 'Hold space' are abbreviated to 'PS' and 'HS', respectively.
Every time we find a line containing PAT, we save it to HS by command 'h' (previously saved line will be overwritten) in [1].
At the end of the file, command 'x' will exchange the contents of PS and HS. Before termination, sed will print the content of PS automatically. The last line containing PAT is listed.
Drawbacks: When the file does NOT have any line containing PAT, this script will print a blank line rather than nothing. Improved version is shown in next script.

Script₂

[ 1] /PAT/h
[ 2] $!d
[ 3] x
[ 4] /^$/d