1	#!/bin/bash
2
3	### Append string to string
4	s='abc'
5	s+=d
6	echo $s
7	# stdout: abcd
8
9	### Append array to array
10	a=(x y )
11	a+=(t 'u v')
12	argv "${a[@]}"
13	# stdout: ['x', 'y', 't', 'u v']
14
15	### Append array to string should be an error
16	s='abc'
17	s+=(d e f)
18	echo $s
19	# BUG bash/mksh stdout: abc
20	# BUG bash/mksh status: 0
21	# status: 1
22
23	### Append string to array should be disallowed
24	# They treat this as implicit index 0. We disallow this on the LHS, so we will
25	# also disallow it on the RHS.
26	a=(x y )
27	a+=z
28	argv "${a[@]}"
29	# OK bash/mksh stdout: ['xz', 'y']
30	# OK bash/mksh status: 0
31	# status: 1
32
33	### Append string to array element
34	# They treat this as implicit index 0. We disallow this on the LHS, so we will
35	# also disallow it on the RHS.
36	a=(x y )
37	a[1]+=z
38	argv "${a[@]}"
39	# stdout: ['x', 'yz']
40	# status: 0
41
42	### Append to last element
43	# Works in bash, but not mksh. It seems like bash is doing the right thing.
44	# a[-1] is allowed on the LHS. mksh doesn't have negative indexing?
45	a=(1 '2 3')
46	a[-1]+=' 4'
47	argv "${a[@]}"
48	# stdout: ['1', '2 3 4']
49	# BUG mksh stdout: ['1', '2 3', ' 4']
50
51	### Try to append list to element
52	# bash - cannot assign list to array number
53	# mksh - a[-1]+: is not an identifier
54	a=(1 '2 3')
55	a[-1]+=(4 5)
56	# status: 1
57
58	### Strings have value semantics, not reference semantics
59	s1='abc'
60	s2=$s1
61	s1+='d'
62	echo $s1 $s2
63	# stdout: abcd abc