Replacing Characters In a String

I have a string field that I need to shorten - typical data looks like '123456-789 XYZ' I can get rid of the XYZ as it is always in the 18,19,20th positions in the string. I need to shorten the field to '123456' but the dash isn't always in the same spot. Can I use the REPLACE function to get rid of everything after the "-"?