Run a command in bg simultaneously with

Hi,
I want to run the command below in the background:

tail -f file.txt | grep "pattern"

The file file.txt will start getting its contents written after this command has started getting run.
So the flow will be like this

tail -f file.txt | grep "pattern"
#The line below will write data to file.txt
./script100.sh

Now if the pattern is found then the user will be notified with some message.
Any idea people?
Thanks a lot :).