You defined the message just before you defined the name, so just do

#. . . other code that does unrelated stuff . . .
$name = "Larry Wall";
$message = "Hello $name\n";
print $message;
[download]

or do like

$message = "Hello ";
#. . . other code that does unrelated stuff . . .
$name = "Larry Wall";
$message .= $name."\n";
print $message;
[download]

Have a nice day
All decision is left to your taste