Write a bash script that takes two DNA strands as arguments and calculates the Hamming distance between them. The Hamming distance is the number of differences between two sequences of equal length. If the sequences are of different lengths, the script should print an error message and exit.

Tip: You can iterate over strings in bash using a for loop with seq (to the number of characters, which you get by using ${#string}) to access each character by its index. You can access the character at index i in a string by using ${string:i:1}.

Example Output:

$ ./hamming_distance.sh GAGCCTACTAACGGGAT CATCGTAATGACGGCCT
The Hamming distance is 7
$ ./hamming_distance.sh GAGCCTACTAACGGGAT CATCGTAATGACGGCC
Error: Sequences must be of equal length