Hello, world!
["target/debug/demo_minigrep", "hello", "poem.txt"]
the content is: 
 “I'm nobody! Who are you?
Are you nobody, too?
Then there's a pair of us - don't tell!
They'd banish us, you know.

How dreary to be somebody!
How public, like a frog
To tell your name the livelong day
To an admiring bog!”