Bash associative array ordering

It appears that the answer is yes, the keys and values will always be in the same order, based on the code I found in Bash version 4.3, assoc.c, available here. The keys and values of the array are retrieved by the functions assoc_keys_to_word_list and assoc_to_word_list, respectively. Both of these functions delegate to assoc_to_word_list_internal, which runs the same loop in both cases, and only differentiates the type of item being retreived based on the t parameter (lines 482-503):

static WORD_LIST *
assoc_to_word_list_internal (h, t)
     HASH_TABLE *h;
     int t;
{
  WORD_LIST *list;
  int i;
  BUCKET_CONTENTS *tlist;
  char *w;

  if (h == 0 || assoc_empty (h))
    return((WORD_LIST *)NULL);
  list = (WORD_LIST *)NULL;

  for (i = 0; i < h->nbuckets; i++)
    for (tlist = hash_items (i, h); tlist; tlist = tlist->next)
      {
  w = (t == 0) ? (char *)tlist->data : (char *)tlist->key;
  list = make_word_list (make_bare_word(w), list);
      }
  return (REVERSE_LIST(list, WORD_LIST *));
}

In case you are wondering, make_word_list is defined in array.c/h. It just appends a new WORD_LIST node to the existing linked list.

While this provides no contractual guarantee that the behavior you expect will always be supported, it is a pretty good indication that you can use your calling convention safely, at least for now. The fact that associative arrays are Bash-only makes the implementation more of a valid reference.

Arrays are not the solution to this problem, especially not associative arrays. Even if they did come out in the same order, you would have multiple keys for a single -k option, resulting in syntax error. Also arrays are a Bashism, and not defined by POSIX. A better solution would be something like this:

./foo.py -k key1,key2,key3 -v val1,val2,val3

Then surely Python can split the input strings? I did something similar with POSIX shell:

tr , '\n' > keys <<eof
$1
eof
tr , '\n' > vals <<eof
$2
eof
paste -d '\n' keys values |
while
  read key
  read val
do
  printf 'key: %s, val: %s\n' "$key" "$val"
done

Of course this would be much easier with Python, as you could just split the strings directly into arrays without using files.