lc $new # lowercase the replacement
^ $1    # XOR with $1 - will increase the values by
        # the corresponding ascii value of each character
        # of $1
^ lc $1 # XOR with lc $1 - basically, it will subract the
        # ascii values of lowercase $1 - if the values were
        # lowercase to begin with, the resulting sum is 0,
        # otherwise, the increase is enough to uppercase
        # the corresponding character