def get_binder_regex(pdb_name, receptor):
    """
    Get binder regex for provided filename.

    e.g. bound 11as_r_u_cleaned.pdb1 would give 11as_r_._cleaned.pdb1.
    """
    new_pdb_name = list(pdb_name)
    new_pdb_name[7] = '.'
    new_pdb_name[5] = 'r' if receptor else 'l'
    new_pdb_name = ['^'] + new_pdb_name + ['$']
    return "".join(new_pdb_name)