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 - runtime error: cannot assign list to array number
53	# mksh - a[-1]+: is not an identifier
54	# osh - parse error -- could be better!
55	a=(1 '2 3')
56	a[-1]+=(4 5)
57	argv.py "${a[@]}"
58	## OK bash STDOUT:
59	['1', '2 3']
60	## END
61	## OK bash status: 0
62	## N-I mksh stdout-json: ""
63	## N-I mksh status: 1
64	## OK stdout-json: ""
65	## OK osh status: 2
66
67	#### Strings have value semantics, not reference semantics
68	s1='abc'
69	s2=$s1
70	s1+='d'
71	echo $s1 $s2
72	## stdout: abcd abc
73
74	#### Append to nonexistent string
75	f() {
76	local a+=a
77	echo $a
78
79	b+=b
80	echo $b
81
82	readonly c+=c
83	echo $c
84
85	export d+=d
86	echo $d
87
88	# Not declared anywhere
89	e[1]+=e
90	echo ${e[1]}
91
92	# Declare is the same, but mksh doesn't support it
93	#declare e+=e
94	#echo $e
95	}
96	f
97	## STDOUT:
98	a
99	b
100	c
101	d
102	e
103	## END
104
105	# += is invalid on assignment builtins
106	## OK osh stdout-json: ""
107	## OK osh status: 1
108
109
110	#### Append to nonexistent array is allowed
111
112	## TODO: strict-array could get rid of this?
113	y+=(c d)
114	argv.py "${y[@]}"
115	## STDOUT:
116	['c', 'd']
117	## END
118
119	#### Append used like env prefix is a parse error
120	# This should be an error in other shells but it's not.
121	A=a
122	A+=a printenv.py A
123	## status: 2
124	## BUG bash stdout: aa
125	## BUG bash status: 0
126	## BUG mksh stdout: a
127	## BUG mksh status: 0