Arrays reference in GNU docs.

Overview

$ MONTHS=("Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" 
  "Aug" "Sep" "Oct" "Nov" "Dec")

Get elements:

$ echo ${MONTHS[9]}
$ echo "${MONTHS[@]}"

Note that using echo or piping to another command will usually mean all the contents are shown on one line.

Create

Create using brackets and spaces:

X=()

X=(abc def ghi)

Or newlines:

X=(abc
def
ghi)

Or the old style.

declare -A X

Slice

Get one element

Any invalid index here returns nothing and also a success code.

In ZSH the index starts at 1.

> echo ${MONTHS[1]}
Jan
> echo ${MONTHS[4]}
Apr

Bash

In Bash it starts at 0.

> echo ${MONTHS[0]}
Jan
> echo ${MONTHS[3]}
Apr

Get all

> echo $MONTHS[@]
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Iterate

Given array:

MY_ARRAY=('abc def' ghi)

New syntax

ZSH and Bash 4.

Remember to add quotes at the start otherwise spaces will be split over newlines.

for X in "$MY_ARRAY[@]"; do
  echo "$X"
done

abc def
ghi

Output all on one line.

for X in "$MY_ARRAY[*]"; do
  echo "$X"
done

abc def ghi

Old

For Bash 3 - you need curly braces. Otherwise you’ll only get the first element.

for X in ${MY_ARRAY[@]}; do
  echo "$X"
done

Or without an array variable:

for X in 'abc def' ghi; do
  echo "$X"
done

abc def
ghi

Modify array

X[2]=zzz
echo $X[2]
# zzz

Convert arguments to an array

MY_ARRAY=("$@")

Based on this StackOverflow thread.

Strings

You can also slice a string.

X=abc
echo "$X[1]"
# a
echo "$X[2]"
# b
echo "$X[@]"
# abc