1	#!/usr/bin/env bash
2
3	#### (( )) result
4	(( 1 )) && echo True
5	(( 0 )) || echo False
6	## stdout-json: "True\nFalse\n"
7
8	#### negative number is true
9	(( -1 )) && echo True
10	## stdout: True
11
12	#### (( )) in if statement
13	if (( 3 > 2)); then
14	echo True
15	fi
16	## stdout: True
17
18	#### (( ))
19	# What is the difference with this and let? One difference: spaces are allowed.
20	(( x = 1 ))
21	(( y = x + 2 ))
22	echo $x $y
23	## stdout: 1 3
24
25	#### (( )) with arrays
26	a=(4 5 6)
27	(( sum = a[0] + a[1] + a[2] ))
28	echo $sum
29	## stdout: 15
30	## OK zsh stdout: 9
31
32	#### (( )) with error
33	(( a = 0 )) || echo false
34	(( b = 1 )) && echo true
35	(( c = -1 )) && echo true
36	echo $((a + b + c))
37	## STDOUT:
38	false
39	true
40	true
41	0
42	## END
43
44
45	#### bash and mksh: V in (( a[K] = V )) gets coerced to integer
46	shopt -u strict_arith || true
47	K=key
48	V=value
49	typeset -a a
50	(( a[K] = V ))
51
52	# not there!
53	echo a[\"key\"]=${a[$K]}
54
55	echo keys = ${!a[@]}
56	echo values = ${a[@]}
57	## STDOUT:
58	a["key"]=0
59	keys = 0
60	values = 0
61	## END
62	## N-I zsh status: 1
63	## N-I zsh stdout-json: ""
64
65	#### bash: K in (( A[K] = V )) is a constant string
66	K=5
67	V=42
68	typeset -A A
69	(( A[K] = V ))
70
71	echo A["5"]=${A["5"]}
72	echo keys = ${!A[@]}
73	echo values = ${A[@]}
74	## STDOUT:
75	A[5]=
76	keys = K
77	values = 42
78	## END
79	## OK osh status: 1
80	## OK osh stdout-json: ""
81	## N-I zsh status: 1
82	## N-I zsh stdout-json: ""
83	## N-I mksh status: 1
84	## N-I mksh stdout-json: ""
85
86	#### BUG: (( V = A[K] )) doesn't retrieve the right value
87	typeset -A A
88	K=5
89	V=42
90	A["$K"]=$V
91	A["K"]=oops
92	A[K]=oops2
93
94	# We don't neither 42 nor "oops". Bad!
95	(( V = A[K] ))
96
97	echo V=$V
98	## status: 1
99	## stdout-json: ""
100	## BUG bash/zsh status: 0
101	## BUG bash/zsh STDOUT:
102	V=0
103	## END
104
105	#### bash: V in (( A["K"] = V )) gets coerced to integer
106	shopt -u strict_arith || true
107	K=key
108	V=value
109	typeset -A A || exit 1
110	(( A["K"] = V ))
111
112	# not there!
113	echo A[\"key\"]=${A[$K]}
114
115	echo keys = ${!A[@]}
116	echo values = ${A[@]}
117	## STDOUT:
118	A["key"]=
119	keys = K
120	values = 0
121	## END
122	## N-I zsh stdout-json: ""
123	## N-I zsh status: 1
124	## N-I mksh stdout-json: ""
125	## N-I mksh status: 1
126
127	#### literal strings not properly supported in ( ))
128	declare -A A
129	A['x']=x
130	(( x = A['x'] ))
131	(( A['y'] = 'y' )) # y is a variable, gets coerced to 0
132	echo $x ${A['y']}
133	## status: 1
134	## stdout-json: ""
135
136	# bash behavior is very confusing
137	## BUG bash status: 0
138	## BUG bash STDOUT:
139	0 0
140	## END
141	## BUG zsh/mksh status: 0
142	## N-I zsh/mksh STDOUT:
143	0
144	## END