Bash Arrays

Declaring and Populating Arrays

You can create an array implicitly by assigning values in parentheses, or explicitly with declare -a name. Indexing starts at zero, and array elements can be strings or numbers, mixed freely since Bash has no strict typing.

#!/bin/bash
declare -a fruits
fruits=("apple" "banana" "cherry")

echo "${fruits[0]}"
echo "${fruits[1]}"

Accessing All Elements and the Length

${arr[@]} expands to every element as separate words, which is ideal for looping. ${#arr[@]} gives the number of elements in the array, and ${!arr[@]} gives the list of valid indices, which is handy when an array has gaps.

#!/bin/bash
fruits=("apple" "banana" "cherry")

echo "Total fruits: ${#fruits[@]}"

for fruit in "${fruits[@]}"; do
  echo "Fruit: $fruit"
done

Adding, Updating, and Removing Elements

Append an element with arr+=("value"), overwrite an existing one by assigning directly to its index, and delete one with unset 'arr[index]'. Note that unset leaves a gap in the indices rather than shifting later elements down.

• arr[0]="value" -- set or overwrite the element at index 0
• arr+=("value") -- append a new element to the end
• unset 'arr[1]' -- remove the element at index 1 (leaves a gap)
• ${arr[@]:1:2} -- slice: 2 elements starting at index 1

#!/bin/bash
colors=("red" "green" "blue")
colors+=("yellow")
colors[1]="lime"
unset 'colors[0]'

for i in "${!colors[@]}"; do
  echo "Index $i: ${colors[$i]}"
done