1
2	#### (( )) result
3	(( 1 )) && echo True
4	(( 0 )) || echo False
5	## stdout-json: "True\nFalse\n"
6
7	#### negative number is true
8	(( -1 )) && echo True
9	## stdout: True
10
11	#### (( )) in if statement
12	if (( 3 > 2)); then
13	echo True
14	fi
15	## stdout: True
16
17	#### (( ))
18	# What is the difference with this and let? One difference: spaces are allowed.
19	(( x = 1 ))
20	(( y = x + 2 ))
21	echo $x $y
22	## stdout: 1 3
23
24	#### (( )) with arrays
25	a=(4 5 6)
26	(( sum = a[0] + a[1] + a[2] ))
27	echo $sum
28	## stdout: 15
29	## OK zsh stdout: 9
30
31	#### (( )) with error
32	(( a = 0 )) || echo false
33	(( b = 1 )) && echo true
34	(( c = -1 )) && echo true
35	echo $((a + b + c))
36	## STDOUT:
37	false
38	true
39	true
40	0
41	## END
42
43
44	#### bash and mksh: V in (( a[K] = V )) gets coerced to integer
45	shopt -u strict_arith || true
46	K=key
47	V=value
48	typeset -a a
49	(( a[K] = V ))
50
51	# not there!
52	echo a[\"key\"]=${a[$K]}
53
54	echo keys = ${!a[@]}
55	echo values = ${a[@]}
56	## STDOUT:
57	a["key"]=0
58	keys = 0
59	values = 0
60	## END
61	## N-I zsh status: 1
62	## N-I zsh stdout-json: ""
63
64	#### bash: K in (( A[K] = V )) is a constant string
65	K=5
66	V=42
67	typeset -A A
68	(( A[K] = V ))
69
70	echo A["5"]=${A["5"]}
71	echo keys = ${!A[@]}
72	echo values = ${A[@]}
73	## STDOUT:
74	A[5]=
75	keys = K
76	values = 42
77	## END
78	## OK osh status: 1
79	## OK osh stdout-json: ""
80	## N-I zsh status: 1
81	## N-I zsh stdout-json: ""
82	## N-I mksh status: 1
83	## N-I mksh stdout-json: ""
84
85	#### BUG: (( V = A[K] )) doesn't retrieve the right value
86	typeset -A A
87	K=5
88	V=42
89	A["$K"]=$V
90	A["K"]=oops
91	A[K]=oops2
92
93	# We don't neither 42 nor "oops". Bad!
94	(( V = A[K] ))
95
96	echo V=$V
97	## status: 1
98	## stdout-json: ""
99	## BUG bash/zsh status: 0
100	## BUG bash/zsh STDOUT:
101	V=0
102	## END
103
104	#### bash: V in (( A["K"] = V )) gets coerced to integer
105	shopt -u strict_arith || true
106	K=key
107	V=value
108	typeset -A A || exit 1
109	(( A["K"] = V ))
110
111	# not there!
112	echo A[\"key\"]=${A[$K]}
113
114	echo keys = ${!A[@]}
115	echo values = ${A[@]}
116	## STDOUT:
117	A["key"]=
118	keys = K
119	values = 0
120	## END
121	## N-I zsh stdout-json: ""
122	## N-I zsh status: 1
123	## N-I mksh stdout-json: ""
124	## N-I mksh status: 1
125
126	#### literal strings inside (( ))
127	declare -A A
128	A['x']=42
129	(( x = A['x'] ))
130	(( A['y'] = 'y' )) # y is a variable, gets coerced to 0
131	echo $x ${A['y']}
132	## STDOUT:
133	42 0
134	## END
135	## BUG mksh status: 0
136	## N-I mksh STDOUT:
137	0
138	## END
139	## BUG zsh status: 0
140	## N-I zsh STDOUT:
141	42
142	## END
143
144	#### (( )) with redirect
145	(( a = $(stdout_stderr.py 42) + 10 )) 2>$TMP/x.txt
146	echo $a
147	echo --
148	cat $TMP/x.txt
149	## STDOUT:
150	52
151	--
152	STDERR
153	## END
154
155	#### Can't make assign whole array to var (( b = a ))
156	a=(4 5 6)
157	(( b = a ))
158	echo "${a[@]}"
159	echo "${b[@]}"
160	## status: 1
161	## stdout-json: ""
162	## BUG bash/mksh status: 0
163	## BUG bash/mksh STDOUT:
164	4 5 6
165	4
166	## END
167	## BUG zsh status: 0
168	## BUG zsh STDOUT:
169	4 5 6
170
171	## END
172
173	#### set associative array
174	declare -A A=(['foo']=bar ['spam']=42)
175	(( x = A['spam'] ))
176	echo $x
177	## STDOUT:
178	42
179	## END
180	## N-I mksh status: 1
181	## N-I mksh stdout-json: ""
182	## N-I zsh STDOUT:
183	0
184	## END
185
186	#### Example of incrementing associative array entry with var key (ble.sh)
187	declare -A A=(['foo']=42)
188	key='foo'
189
190	# note: in bash, (( A[\$key] += 1 )) works the same way.
191
192	set -- 1 2
193	(( A[$key] += $2 ))
194
195	echo foo=${A['foo']}
196
197	## STDOUT:
198	foo=44
199	## END
200	## N-I mksh/zsh status: 1
201	## N-I mksh/zsh stdout-json: ""
202