Joining two files without a common value

I want to join two files based on a field of file 1 containing the value of a field in file 2. What would be the best way to do this?
e.g.
File 1: $district_name='ABC School District". File 2: $district: ‘ABC’.
So if $district_name.contains($district). I want to set $new_district in File 1 to $district