1	#!/usr/bin/env bash
2	#
3	# Arrays decay upon assignment (without splicing) and equality. This will not
4	# be true in Oil -- arrays will be first class.
5
6	#### Assignment Causes Array Decay
7	set -- x y z
8	argv.py "[$@]"
9	var="[$@]"
10	argv.py "$var"
11	## STDOUT:
12	['[x', 'y', 'z]']
13	['[x y z]']
14	## END
15
16	#### Array Decay with IFS
17	IFS=x
18	set -- x y z
19	var="[$@]"
20	argv.py "$var"
21	## stdout: ['[x y z]']
22
23	#### User arrays decay
24	declare -a a b
25	a=(x y z)
26	b="${a[@]}" # this collapses to a string
27	c=("${a[@]}") # this preserves the array
28	c[1]=YYY # mutate a copy -- doesn't affect the original
29	argv.py "${a[@]}"
30	argv.py "${b[@]}"
31	argv.py "${c[@]}"
32	## STDOUT:
33	['x', 'y', 'z']
34	['x y z']
35	['x', 'YYY', 'z']
36	## END
37
38	#### $a gives first element of array
39	a=(1 '2 3')
40	echo $a
41	## stdout: 1
42
43	#### Assign to array index without initialization
44	a[5]=5
45	a[6]=6
46	echo "${a[@]}" ${#a[@]}
47	## stdout: 5 6 2
48
49	#### a[40] grows array
50	a=(1 2 3)
51	a[1]=5
52	a[40]=30 # out of order
53	a[10]=20
54	echo "${a[@]}" "${#a[@]}" # length is 1
55	## stdout: 1 5 3 20 30 5
56
57	#### array decays to string when comparing with [[ a = b ]]
58	a=('1 2' '3 4')
59	s='1 2 3 4' # length 2, length 4
60	echo ${#a[@]} ${#s}
61	[[ "${a[@]}" = "$s" ]] && echo EQUAL
62	## STDOUT:
63	2 7
64	EQUAL
65	## END
66
67	#### Increment array variables
68	a=(1 2)
69	(( a++ )) # doesn't make sense
70	echo "${a[@]}"
71	## stdout: 2 2
72
73	#### Apply vectorized operations on ${a[*]}
74	a=('-x-' 'y-y' '-z-')
75
76	# This does the prefix stripping FIRST, and then it joins.
77	argv.py "${a[*]#-}"
78	## STDOUT:
79	['x- y-y z-']
80	## END
81	## N-I mksh status: 1
82	## N-I mksh stdout-json: ""