Regular expression for Zipcode

hi
 
in my application i have a field Zipcode.
for that i have to apply regular expression.
the format will be   5digit number-4 digit number
here the 5 digit no is must and the '-' and 4 digit no is optional.
 
i tried with \d{5}-\d*. but here when i enter only 5 digits it is not working
 
help me in this
 
Thanks in Advance
Radha.


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