local s = "foo"

local t = {}
for i=1,#s do
  t[i] = s:sub(i,i)
end

function split (s, delim)

  assert (type (delim) == "string" and string.len (delim) > 0,
          "bad delimiter")

  local start = 1
  local t = {}  -- results table

  -- find each instance of a string followed by the delimiter

  while true do
    local pos = string.find (s, delim, start, true) -- plain find

    if not pos then
      break
    end

    table.insert (t, string.sub (s, start, pos - 1))
    start = pos + string.len (delim)
  end -- while

  -- insert final one (after last delimiter)

  table.insert (t, string.sub (s, start))

  return t
 
end -- function split

static int l_split (lua_State *L) {
  const char *s = luaL_checkstring(L, 1);
  const char *sep = luaL_checkstring(L, 2);
  const int count = (int) luaL_optnumber (L, 3, 0);
  char *e;
  int i = 1;

  if (strlen (sep) != 1)
    luaL_error (L, "Separator must be a single character");

  if (count < 0)
    luaL_error (L, "Count must be positive or zero");

  lua_newtable(L);  /* result */

  /* repeat for each separator */
  while ((e = strchr(s, *sep)) != NULL && 
         (count == 0 || i <= count)) 
    {
    lua_pushlstring(L, s, e-s);  /* push substring */
    lua_rawseti(L, -2, i++);
    s = e + 1;  /* skip separator */
    }

  /* push last substring */
  lua_pushstring(L, s);
  lua_rawseti(L, -2, i);

  return 1;  /* return the table */
}

test = "the,quick,brown,dog,jumped"  

t = utils.split (test, ",")

tprint (t)

print (table.concat (t, ","))

Output:

1="the"
2="quick"
3="brown"
4="dog"
5="jumped"

the,quick,brown,dog,jumped

t = utils.split (test, ",", 2)

tprint (t)

Output:

1="the"
2="quick"
3="brown,dog,jumped"