[RBASE-L] - postal service zipcodes

[Ray2Hartman]

Our database has 1 column for the 5 digit zipcode and 1 column for the 4 digit extension. The 4 digit extension is sometimes blank - unknown. I have been printing mail lables with these two columns separated by a space. Our local post office has informed us that this is not acceptable for their scanning equipment. There must be a hyphen between the two when both are present. Of course this is easy, except when the 4 digit extension is blank, then the hyphen should not be present. Can I use a variable _expression_ for this?