how can I prepend a string?

[Twey]

Also is more efficient.

[djr33]

Though you now have your answer, you've entirely overthought this:
$a = 'abc'; $b = 'xyz';
$a.$b becomes 'abcxyz'

To insert a space, that is another step, using $a.' '.$b

And of course you'll have to pick what value is $a, and what is $b.

In short, using the . operator will add two strings.

And as Twey has pointed out, the .= is just a shortcut to $a = $a.$b;. There is no shortcut for using =., and equivalent of $a = $b.$a;