Changing the first letter of every line in a file to uppercase

Question

I need to change the first letter of every line in a file to uppercase, e.g.

the bear ate the fish.
the river was too fast.

Would become:

Answer 1

There's a few sed answers with s/^\(.\)/\U\1/. GNU sed also has a \u directive that changes only the next letter to uppercase, so

sed 's/./\u&/'

Although if the first character on a line is a space, you won't see an uppercase letter, so

sed 's/[[:alpha:]]/\u&/'