1	#!/usr/bin/env bash
2	#
3	# Interesting interpretation of constants.
4	#
5	# "Constants with a leading 0 are interpreted as octal numbers. A leading ‘0x’
6	# or ‘0X’ denotes hexadecimal. Otherwise, numbers take the form [base#]n, where
7	# the optional base is a decimal number between 2 and 64 representing the
8	# arithmetic base, and n is a number in that base. If base# is omitted, then
9	# base 10 is used. When specifying n, the digits greater than 9 are represented
10	# by the lowercase letters, the uppercase letters, ‘@’, and ‘_’, in that order.
11	# If base is less than or equal to 36, lowercase and uppercase letters may be
12	# used interchangeably to represent numbers between 10 and 35. "
13	#
14	# NOTE $(( 8#9 )) can fail, and this can be done at parse time...
15
16	#### Side Effect in Array Indexing
17	a=(4 5 6)
18	echo "${a[b=2]} b=$b"
19	## stdout: 6 b=2
20	## OK zsh stdout: 5 b=2
21	## N-I dash stdout-json: ""
22	## N-I dash status: 2
23
24	#### Add one to var
25	i=1
26	echo $(($i+1))
27	## stdout: 2
28
29	#### $ is optional
30	i=1
31	echo $((i+1))
32	## stdout: 2
33
34	#### SimpleVarSub within arith
35	echo $(($j + 1))
36	## stdout: 1
37
38	#### BracedVarSub within ArithSub
39	echo $((${j:-5} + 1))
40	## stdout: 6
41
42	#### Arith word part
43	foo=1; echo $((foo+1))bar$(($foo+1))
44	## stdout: 2bar2
45
46	#### Arith sub with word parts
47	# Making 13 from two different kinds of sub. Geez.
48	echo $((1 + $(echo 1)${undefined:-3}))
49	## stdout: 14
50
51	#### Constant with quotes like '1'
52	# NOTE: Compare with [[. That is a COMMAND level expression, while this is a
53	# WORD level expression.
54	echo $(('1' + 2))
55	## status: 0
56	## N-I bash/zsh status: 1
57	## N-I dash status: 2
58
59	#### Arith sub within arith sub
60	# This is unnecessary but works in all shells.
61	echo $((1 + $((2 + 3)) + 4))
62	## stdout: 10
63
64	#### Backticks within arith sub
65	# This is unnecessary but works in all shells.
66	echo $((`echo 1` + 2))
67	## stdout: 3
68
69	#### Invalid string to int
70	# bash, mksh, and zsh all treat strings that don't look like numbers as zero.
71	s=foo
72	echo $((s+5))
73	## OK dash stdout-json: ""
74	## OK dash status: 2
75	## OK bash/mksh/zsh/osh stdout: 5
76	## OK bash/mksh/zsh/osh status: 0
77
78	#### Invalid string to int with strict-arith
79	set -o strict-arith || true
80	s=foo
81	echo $s
82	echo $((s+5))
83	echo 'should not get here'
84	## status: 1
85	## stdout-json: "foo\n"
86	## N-I bash status: 0
87	## N-I bash STDOUT:
88	foo
89	5
90	should not get here
91	## END
92	## N-I dash status: 2
93	## N-I dash stdout-json: ""
94	## N-I mksh status: 1
95	## N-I mksh stdout-json: ""
96	## N-I zsh status: 1
97	## N-I zsh stdout-json: ""
98
99	#### Newline in the middle of expression
100	echo $((1
101	+ 2))
102	## stdout: 3
103
104	#### Ternary operator
105	a=1
106	b=2
107	echo $((a>b?5:10))
108	## stdout: 10
109
110	#### Preincrement
111	a=4
112	echo $((++a))
113	echo $a
114	## stdout-json: "5\n5\n"
115	## N-I dash status: 0
116	## N-I dash stdout-json: "4\n4\n"
117
118	#### Postincrement
119	a=4
120	echo $((a++))
121	echo $a
122	## stdout-json: "4\n5\n"
123	## N-I dash status: 2
124	## N-I dash stdout-json: ""
125
126	#### Increment undefined variables
127	(( undef1++ ))
128	(( ++undef2 ))
129	echo "[$undef1][$undef2]"
130	## stdout: [1][1]
131	## N-I dash stdout-json: "[][]\n"
132
133	#### Increment and decrement array
134	a=(5 6 7 8)
135	(( a[0]++, ++a[1], a[2]--, --a[3] ))
136	(( undef[0]++, ++undef[1], undef[2]--, --undef[3] ))
137	echo "${a[@]}" - "${undef[@]}"
138	## stdout: 6 7 6 7 - 1 1 -1 -1
139	## N-I dash stdout-json: ""
140	## N-I dash status: 2
141	## BUG zsh stdout: 5 6 7 8 -
142
143	#### Increment undefined variables with nounset
144	set -o nounset
145	(( undef1++ ))
146	(( ++undef2 ))
147	echo "[$undef1][$undef2]"
148	## stdout-json: ""
149	## status: 1
150	## OK dash status: 2
151	## BUG mksh/zsh status: 0
152	## BUG mksh/zsh stdout-json: "[1][1]\n"
153
154	#### Comma operator (borrowed from C)
155	a=1
156	b=2
157	echo $((a,(b+1)))
158	## stdout: 3
159	## N-I dash status: 2
160	## N-I dash stdout-json: ""
161
162	#### Augmented assignment
163	a=4
164	echo $((a+=1))
165	echo $a
166	## stdout-json: "5\n5\n"
167
168	#### Comparison Ops
169	echo $(( 1 == 1 ))
170	echo $(( 1 != 1 ))
171	echo $(( 1 < 1 ))
172	echo $(( 1 <= 1 ))
173	echo $(( 1 > 1 ))
174	echo $(( 1 >= 1 ))
175	## stdout-json: "1\n0\n0\n1\n0\n1\n"
176
177	#### Logical Ops
178	echo $((1 || 2))
179	echo $((1 && 2))
180	echo $((!(1 || 2)))
181	## stdout-json: "1\n1\n0\n"
182
183	#### Logical Ops Short Circuit
184	x=11
185	(( 1 || (x = 22) ))
186	echo $x
187	(( 0 || (x = 33) ))
188	echo $x
189	(( 0 && (x = 44) ))
190	echo $x
191	(( 1 && (x = 55) ))
192	echo $x
193	## stdout-json: "11\n33\n33\n55\n"
194	## N-I dash stdout-json: "11\n11\n11\n11\n"
195
196	#### Bitwise ops
197	echo $((1|2))
198	echo $((1&2))
199	echo $((1^2))
200	echo $((~(1|2)))
201	## stdout-json: "3\n0\n3\n-4\n"
202
203	#### Unary minus and plus
204	a=1
205	b=3
206	echo $((- a + + b))
207	## stdout-json: "2\n"
208
209	#### No floating point
210	echo $((1 + 2.3))
211	## status: 2
212	## OK bash/mksh status: 1
213	## BUG zsh status: 0
214
215	#### Array indexing in arith
216	# zsh does 1-based indexing!
217	array=(1 2 3 4)
218	echo $((array[1] + array[2]*3))
219	## stdout: 11
220	## OK zsh stdout: 7
221	## N-I dash status: 2
222	## N-I dash stdout-json: ""
223
224	#### Constants in base 36
225	echo $((36#a))-$((36#z))
226	## stdout: 10-35
227	## N-I dash stdout-json: ""
228	## N-I dash status: 2
229
230	#### Constants in bases 2 to 64
231	# This is a truly bizarre syntax. Oh it comes from zsh... which allows 36.
232	echo $((64#a))-$((64#z)), $((64#A))-$((64#Z)), $((64#@)), $(( 64#_ ))
233	## stdout: 10-35, 36-61, 62, 63
234	## N-I dash stdout-json: ""
235	## N-I dash status: 2
236	## N-I mksh/zsh stdout-json: ""
237	## N-I mksh/zsh status: 1
238
239	#### Dynamic base constants
240	base=16
241	echo $(( ${base}#a ))
242	## stdout: 10
243	## N-I dash stdout-json: ""
244	## N-I dash status: 2
245
246	#### Octal constant
247	echo $(( 011 ))
248	## stdout: 9
249	## N-I mksh/zsh stdout: 11
250
251	#### Dynamic octal constant
252	zero=0
253	echo $(( ${zero}11 ))
254	## stdout: 9
255	## N-I mksh/zsh stdout: 11
256
257	#### Dynamic hex constants
258	zero=0
259	echo $(( ${zero}xAB ))
260	## stdout: 171
261
262	#### Dynamic var names - result of runtime parse/eval
263	foo=5
264	x=oo
265	echo $(( foo + f$x + 1 ))
266	## stdout: 11
267	## OK osh stdout: 6
268
269	#### Bizarre recursive name evaluation - result of runtime parse/eval
270	foo=5
271	bar=foo
272	spam=bar
273	eggs=spam
274	echo $((foo+1)) $((bar+1)) $((spam+1)) $((eggs+1))
275	## stdout: 6 6 6 6
276	## OK osh stdout: 6 1 1 1
277	## N-I dash stdout-json: ""
278	## N-I dash status: 2
279
280	#### nounset with arithmetic
281	set -o nounset
282	x=$(( y + 5 ))
283	echo "should not get here: x=${x:-<unset>}"
284	## stdout-json: ""
285	## status: 1
286	## BUG dash/mksh/zsh stdout: should not get here: x=5
287	## BUG dash/mksh/zsh status: 0
288
289	#### Integer Overflow
290	set -o nounset
291	echo $(( 999999 * 999999 * 999999 * 999999 ))
292	## stdout: 999996000005999996000001
293	## BUG dash/bash/zsh stdout: -1996229794797103359
294	## BUG mksh stdout: -15640831
295
296	#### Invalid LValue
297	a=9
298	(( (a + 2) = 3 ))
299	echo $a
300	## status: 2
301	## stdout-json: ""
302	## OK bash/mksh/zsh stdout: 9
303	## OK bash/mksh/zsh status: 0
304	# dash doesn't implement assignment
305	## N-I dash status: 2
306	## N-I dash stdout-json: ""
307
308	#### Invalid LValue that looks like array
309	(( 1[2] = 3 ))
310	echo "status=$?"
311	## status: 2
312	## stdout-json: ""
313	## OK bash stdout: status=1
314	## OK bash status: 0
315	## OK mksh/zsh stdout: status=2
316	## OK mksh/zsh status: 0
317	## N-I dash stdout: status=127
318	## N-I dash status: 0
319
320	#### Invalid LValue: two sets of brackets
321	(( a[1][2] = 3 ))
322	echo "status=$?"
323	# shells treat this as a NON-fatal error
324	## status: 2
325	## stdout-json: ""
326	## OK bash stdout: status=1
327	## OK mksh/zsh stdout: status=2
328	## OK bash/mksh/zsh status: 0
329	# dash doesn't implement assignment
330	## N-I dash stdout: status=127
331	## N-I dash status: 0
332
333	#### Operator Precedence
334	echo $(( 1 + 2*3 - 8/2 ))
335	## stdout: 3
336
337	#### Exponentiation with **
338	echo $(( 3 ** 0 ))
339	echo $(( 3 ** 1 ))
340	echo $(( 3 ** 2 ))
341	## STDOUT:
342	1
343	3
344	9
345	## END
346	## N-I dash stdout-json: ""
347	## N-I dash status: 2
348	## N-I mksh stdout-json: ""
349	## N-I mksh status: 1
350
351	#### Exponentiation operator has buggy precedence
352	# NOTE: All shells agree on this, but R and Python give -9, which is more
353	# mathematically correct.
354	echo $(( -3 ** 2 ))
355	## osh stdout: 9
356	## N-I dash stdout-json: ""
357	## N-I dash status: 2
358	## N-I mksh stdout-json: ""
359	## N-I mksh status: 1
360
361	#### Negative exponent
362	# bash explicitly disallows negative exponents!
363	echo $(( 2**-1 * 5 ))
364	## stdout-json: ""
365	## status: 1
366	## OK zsh stdout: 2.5
367	## OK zsh status: 0
368	## N-I dash stdout-json: ""
369	## N-I dash status: 2
370
371	#### Comment not allowed in the middle of multiline arithmetic
372	echo $((
373	1 +
374	2 + \
375	3
376	))
377	echo $((
378	1 + 2 # not a comment
379	))
380	(( a = 3 + 4 # comment
381	))
382	echo [$a]
383	## status: 1
384	## STDOUT:
385	6
386	## END
387	## OK dash/osh status: 2
388	## OK bash STDOUT:
389	6
390	[]
391	## END
392	## OK bash status: 0