flipping the names around in php

ok so i have a user field that has the user enter the full name and i need to flip the names around

 $pieces = explode(" ", $_POST['realname']);
 name = stripslashes($pieces[1] . "-" . $pieces[0]);

but the problem is that if they type in the field

i need the final output as jones-mark for sake of the requirements or if there is only m开发者_运维知识库ark then i need mark

mark jones

all is well but if they type

mark 

then the output is

-mark

im sure there is a better way to do this

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implode("-",array_reverse($pieces))