1	#!/bin/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 "[$@]" # NOT DECAYED here.
9	var="[$@]"
10	argv.py "$var"
11	# stdout: ['[x y z]']
12
13	### User arrays decay
14	declare -a a b
15	a=(x y z)
16	b="${a[@]}" # this collapses to a string
17	c=("${a[@]}") # this preserves the array
18	c[1]=YYY # mutate a copy -- doesn't affect the original
19	argv.py "${a[@]}" "${b[@]}" "${c[@]}"
20	# stdout: ['x', 'y', 'z', 'x y z', 'x', 'YYY', 'z']
21
22	### $a gives first element of array
23	a=(1 '2 3')
24	echo $a
25	# stdout: 1
26
27	### Assign to array index without initialization
28	a[5]=5
29	a[6]=6
30	echo "${a[@]}" ${#a[@]}
31	# stdout: 5 6 2
32
33	### a[40] grows array
34	a=(1 2 3)
35	a[1]=5
36	a[40]=30 # out of order
37	a[10]=20
38	echo "${a[@]}" "${#a[@]}" # length is 1
39	# stdout: 1 5 3 20 30 5
40
41	### array decays to string when comparing with [[ a = b ]]
42	a=('1 2' '3 4')
43	s='1 2 3 4' # length 2, length 4
44	echo ${#a[@]} ${#s}
45	[[ "${a[@]}" = "$s" ]] && echo EQUAL
46	# stdout-json: "2 7\nEQUAL\n"
47
48	### Increment array variables
49	a=(1 2)
50	(( a++ )) # doesn't make sense
51	echo "${a[@]}"
52	# stdout: 2 2
53