1	#!/bin/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	### Add one to var
17	i=1
18	echo $(($i+1))
19	# stdout: 2
20
21	### $ is optional
22	i=1
23	echo $((i+1))
24	# stdout: 2
25
26	### Bizarre recursive evaluation rule
27	foo=5
28	bar=foo
29	spam=bar
30	eggs=spam
31	echo $((foo+1)) $((bar+1)) $((spam+1)) $((eggs+1))
32	# stdout: 6 6 6 6
33	# N-I dash stdout-json: ""
34	# N-I dash status: 2
35
36	### Can use Braced VarSub within ArithSub
37	echo $((${j:-5} + 1))
38	# stdout: 6
39
40	### Arith word part
41	foo=1; echo $((foo+1))bar$(($foo+1))
42	# stdout: 2bar2
43
44	### Arith sub with word parts
45	# Making 13 from two different kinds of sub. Geez.
46	echo $((1 + $(echo 1)${undefined:-3}))
47	# stdout: 14
48
49	### Constant with quotes like '1'
50	# NOTE: Compare with [[. That is a COMMAND level expression, while this is a
51	# WORD level expression.
52	echo $(('1' + 2))
53	# status: 0
54	# N-I bash/zsh status: 1
55	# N-I dash status: 2
56
57	### Arith sub within arith sub
58	# This is unnecessary but works in all shells.
59	echo $((1 + $((2 + 3)) + 4))
60	# stdout: 10
61
62	### Backticks within arith sub
63	# This is unnecessary but works in all shells.
64	echo $((`echo 1` + 2))
65	# stdout: 3
66
67	### Bad variable substitution
68	# Hm bash, mksh, and zsh ignore the variable. They treat it as 0?
69	s=foo
70	echo $((s+5))
71	# status: 1
72	# OK dash status: 2
73	# BUG bash/mksh/zsh status: 0
74
75	### Two bad variable substitutions
76	s=foo
77	t=bar
78	echo $((s+t))
79	# status: 1
80	# OK dash status: 2
81	# BUG bash/mksh/zsh status: 0
82
83	### Newline in the middle of expression
84	echo $((1
85	+ 2))
86	# stdout: 3
87
88	### Ternary operator
89	a=1
90	b=2
91	echo $((a>b?5:10))
92	# stdout: 10
93
94	### Preincrement
95	a=4
96	echo $((++a))
97	echo $a
98	# stdout-json: "5\n5\n"
99	# N-I dash status: 0
100	# N-I dash stdout-json: "4\n4\n"
101
102	### Postincrement
103	a=4
104	echo $((a++))
105	echo $a
106	# stdout-json: "4\n5\n"
107	# N-I dash status: 2
108	# N-I dash stdout-json: ""
109
110	### Comma operator (borrowed from C)
111	a=1
112	b=2
113	echo $((a,(b+1)))
114	# stdout: 3
115	# N-I dash status: 2
116	# N-I dash stdout-json: ""
117
118	### Mutating ops
119	a=4
120	echo $((a+=1))
121	echo $a
122	# stdout-json: "5\n5\n"
123
124	### Bitwise ops
125	echo $((1|2))
126	echo $((1&2))
127	echo $((~(1|2)))
128	# stdout-json: "3\n0\n-4\n"
129
130	### Unary minus and plus
131	a=1
132	b=3
133	echo $((- a + + b))
134	# stdout-json: "2\n"
135
136	### No floating point
137	echo $((1 + 2.3))
138	# status: 1
139	# OK dash status: 2
140	# BUG zsh status: 0
141
142	### Array indexing in arith
143	# zsh does 1-based indexing!
144	array=(1 2 3 4)
145	echo $((array[1] + array[2]*3))
146	# stdout: 11
147	# OK zsh stdout: 7
148	# N-I dash status: 2
149	# N-I dash stdout-json: ""
150
151	### Constants in base 36
152	echo $((36#a))-$((36#z))
153	# stdout: 10-35
154	# N-I dash stdout-json: ""
155	# N-I dash status: 2
156
157	### Constants in bases 2 to 64
158	# This is a truly bizarre syntax. Oh it comes from zsh... which allows 36.
159	echo $((64#a))-$((64#z)), $((64#A))-$((64#Z)), $((64#@)), $(( 64#_ ))
160	# stdout: 10-35, 36-61, 62, 63
161	# N-I dash stdout-json: ""
162	# N-I dash status: 2
163	# N-I mksh/zsh stdout-json: ""
164	# N-I mksh/zsh status: 1
165
166	### Dynamic base constants
167	base=16
168	echo $(( ${base}#a ))
169	# stdout: 10
170	# N-I dash stdout-json: ""
171	# N-I dash status: 2
172
173	### Octal constant
174	echo $(( 011 ))
175	# stdout: 9
176	# N-I mksh/zsh stdout: 11
177
178	### Dynamic octal constant
179	zero=0
180	echo $(( ${zero}11 ))
181	# stdout: 9
182	# N-I mksh/zsh stdout: 11
183
184	### Dynamic hex constants
185	zero=0
186	echo $(( ${zero}xAB ))
187	# stdout: 171
188
189	### Dynamic var names!
190	foo=5
191	x=oo
192	echo $(( foo + f$x + 1 ))
193	# stdout: 11