Combining numeric values

One of our physical files has a field that is used for holding SSN data,
9 characters in length with no decimals.

With cgi, we are parsing the data into three separate variables to
ensure the length is correct and contains only numeric values..IE: SS1 3
characters in length, SS2 2 characters in length and SS3 4 characters in
length.

Where I am stumped is attempting to combine these into a fourth so that
if I have 123-45-6789 as a SSN it will come in via the browser as
SS1=123, SS2=45, SS3=6789 I can turn it into 123456789.

I thought about defining the variables as character type and then
concatenate them with an EVAL statement and then just write it to the
PF...anyone have any issues with this?  Any suggestions would be
appreciated.

Douglas