This song is from the "o brother where art thou" soundtrack.
There's a dark & a troubled side of life
There's a bright, there's a sunny side, too
Tho' we meet with the darkness and strife
The sunny side we also may view
Keep on the sunny side, always on the sunny side,
Keep on the sunny side of life
It will help us ev'ry day, it will brighten all the way
If we'll keep on the sunny side of life
Solo (same as the intro)