You can also use the method form if you are more a Java(Script) guy:

use v6;
my $x = "this is a test".subst(/\s/, '-', :g);

# or 

my $x = "this is a test";
$x.=subst(/\s/, '-', :g);
[download]

The second example calls the subst method on $x (that's why you see a dot), and then mutates it (the equal sign).

:g is again the adverb for global matching, like in s:g///.