1	#!/usr/bin/env bash
2
3	#### Append string to string
4	s='abc'
5	s+=d
6	echo $s
7	## stdout: abcd
8
9	#### Append array to array
10	a=(x y )
11	a+=(t 'u v')
12	argv.py "${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 $s
19	## BUG bash/mksh stdout: abc
20	## BUG bash/mksh status: 0
21	## status: 1
22
23	#### Append string to array should be disallowed
24	# They treat this as implicit index 0. We disallow this on the LHS, so we will
25	# also disallow it on the RHS.
26	a=(x y )
27	a+=z
28	argv.py "${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.py "${a[@]}"
39	## stdout: ['x', 'yz']
40	## status: 0
41
42	#### Append to last element
43	# Works in bash, but not mksh. It seems like bash is doing the right thing.
44	# a[-1] is allowed on the LHS. mksh doesn't have negative indexing?
45	a=(1 '2 3')
46	a[-1]+=' 4'
47	argv.py "${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
64
65	#### Append to nonexistent string
66	f() {
67	local a+=a
68	echo $a
69
70	b+=b
71	echo $b
72
73	readonly c+=c
74	echo $c
75
76	export d+=d
77	echo $d
78
79	# Not declared anywhere
80	e[1]+=e
81	echo ${e[1]}
82
83	# Declare is the same, but mksh doesn't support it
84	#declare e+=e
85	#echo $e
86	}
87	f
88	## stdout-json: "a\nb\nc\nd\ne\n"
89
90	#### Append to nonexistent array
91	f() {
92	# NOTE: mksh doesn't like a=() after keyword. Doesn't allow local arrays!
93	local x+=(a b)
94	argv.py "${x[@]}"
95
96	y+=(c d)
97	argv.py "${y[@]}"
98
99	readonly z+=(e f)
100	argv.py "${z[@]}"
101	}
102	f
103	## stdout-json: "['a', 'b']\n['c', 'd']\n['e', 'f']\n"
104	## N-I mksh stdout-json: ""
105	## N-I mksh status: 1
106
107	#### Append used like env prefix is a parse error
108	# This should be an error in other shells but it's not.
109	A=a
110	A+=a printenv.py A
111	## status: 2
112	## BUG bash stdout: aa
113	## BUG bash status: 0
114	## BUG mksh stdout: a
115	## BUG mksh status: 0