If you are not familiar with lists, check out our article Getting Started with Lists in Bash Shell Scripting.

Let's say you have a list of fruit. += can be used to append values to a list. In this example, pineapple is appended to the "fruit" list.

declare will return the structure of the list and echo will be used to print each value in the list.

fruit=(banana apple orange grapes)
fruit+=(pineapple)
declare -p fruit
echo ${fruit[*]}

Running this script should return the following.

declare -a fruit=([0]="banana" [1]="apple" [2]="orange" [3]="grapes" [4]="pineapple")
banana apple orange grapes pineapple

By default, whitespace is used to delimit the elements in the list.

#!/bin/bash
fruit=(banana apple orange grapes)
fruit+=(pineapple pears)
declare -p fruit
echo ${fruit[*]}

In this example, "pineapple" and "pears" will be unique elements in the list.

declare -a fruit=([0]="banana" [1]="apple" [2]="orange" [3]="grapes" [4]="pineapple" [5]="pears")
banana apple orange grapes pineapple pears

single or double quotes can be used to append a value that contains whitespace to the list.

#!/bin/bash
fruit=(banana apple orange grapes)
fruit+=("pineapple pears")
declare -p fruit
echo ${fruit[*]}

Or a for loop can be used to iterate over each item in the list, like this.

By default, the Internal Field Separator, commonly known as IFS, uses whitespace as the delimiter, so I often have to update IFS to use new lines as the delimiter.

IFS=$'\n'
for item in ${fruit[@]}; do
  echo $item
done
unset IFS

Which should return the following.

apple
banana
orange
grape
pineapple pears