One necessity is dealing with Arrays as a data structure in any kind of language or interpreter. The Linux Documentation Project has lots of documentation, but lacks IMHO concise and straightforward examples. I created this example, as recently I have struggled myself how to operate on arrays. I spice it up with some ASCII art from asky.io (♥_♥).

The Example Program

I wrote this example on my MacBook Pro, which has two flavours of Linux Shell: Bash and Z shell (zsh).

There are minor differences in the feature set. The most important one:

• zsh arrays start at index position 1
• bash arrays start at index position 0

See a more detailed answer to that problem. Regardless pay attention, if you are using different shells.

Bash

Run with sh array-demo.sh:

detecting shell:
  using bash 3.2.57(1)-release

array: ¯\_(ツ)_/¯ This is a string array ᕙ(⇀‸↼‶)ᕗ

index 5: array

length: 7

last index: ᕙ(⇀‸↼‶)ᕗ

item: ¯\_(ツ)_/¯ has a length of 9

iterate over array
  ¯\_(ツ)_/¯
  This
  is
  a
  string
  array
  ᕙ(⇀‸↼‶)ᕗ

iterate with index
index: 0, value: ¯\_(ツ)_/¯
index: 1, value: This
index: 2, value: is
index: 3, value: a
index: 4, value: string
index: 5, value: array
index: 6, value: ᕙ(⇀‸↼‶)ᕗ

zsh

Run with zsh array-demo.sh:

detecting shell:
  using zsh 5.3

array: ¯\_(ツ)_/¯ This is a string array ᕙ(⇀‸↼‶)ᕗ

index 5: string

length: 7

last index: array

item:  has a length of 0

iterate over array
  ¯\_(ツ)_/¯
  This
  is
  a
  string
  array
  ᕙ(⇀‸↼‶)ᕗ

The major differences to bash:

• at index 5 the value is string instead of array
• the last value array is not correct, we expect ᕙ(⇀‸↼‶)ᕗ
• the first item of index 0 is empty since the index in zsh starts with 1
• Iteration with index does not work for the zsh.

Resolve Issues

For the educational purpose, I use the variables INDEX_START and INDEX_OFFSET to accomplish identical results.

detecting shell:
  using bash 3.2.57(1)-release, index starts at 0

array: ¯\_(ツ)_/¯ This is a string array ᕙ(⇀‸↼‶)ᕗ

index 5: string

length: 7

last index: ᕙ(⇀‸↼‶)ᕗ

item: ¯\_(ツ)_/¯ has a length of 9

iterate over array
  ¯\_(ツ)_/¯
  This
  is
  a
  string
  array
  ᕙ(⇀‸↼‶)ᕗ

iterate with index
index: 0, value: ¯\_(ツ)_/¯
index: 1, value: This
index: 2, value: is
index: 3, value: a
index: 4, value: string
index: 5, value: array
index: 6, value: ᕙ(⇀‸↼‶)ᕗ

detecting shell:
  using zsh 5.3, index starts at 1

array: ¯\_(ツ)_/¯ This is a string array ᕙ(⇀‸↼‶)ᕗ

index 5: string

length: 7

last index: ᕙ(⇀‸↼‶)ᕗ

item: ¯\_(ツ)_/¯ has a length of 9

iterate over array
  ¯\_(ツ)_/¯
  This
  is
  a
  string
  array
  ᕙ(⇀‸↼‶)ᕗ

iterate with index
index: 1, value: ¯\_(ツ)_/¯
index: 2, value: This
index: 3, value: is
index: 4, value: a
index: 5, value: string
index: 6, value: array
index: 7, value: ᕙ(⇀‸↼‶)ᕗ

Compare with diff

To compare the two outputs, if your eye doesn't see the difference ＼ ٩( ᐛ )و /／.

diff <(sh array-demo-improved.sh) <(zsh array-demo-improved.sh) 

Output:

2c2
<   using bash 3.2.57(1)-release, index starts at 0
---
>   using zsh 5.3, index starts at 1
24,30c24,30
< index: 0, value: ¯\_(ツ)_/¯
< index: 1, value: This
< index: 2, value: is
< index: 3, value: a
< index: 4, value: string
< index: 5, value: array
< index: 6, value: ᕙ(⇀‸↼‶)ᕗ
---
> index: 1, value: ¯\_(ツ)_/¯
> index: 2, value: This
> index: 3, value: is
> index: 4, value: a
> index: 5, value: string
> index: 6, value: array
> index: 7, value: ᕙ(⇀‸↼‶)ᕗ

Side by Side diff

diff -y <(sh array-demo-improved.sh) <(zsh array-demo-improved.sh) 

For the popcorn geeks: