Bash Arrays

Arrays are one of the most commonly used and fundamental data structures. You can think of an array as a variable that stores multiple values, allowing you to represent and manipulate a group of related data as a single entity.

Bash supports two types of arrays: numerically indexed arrays referenced by integers, and associative arrays referenced by strings (keys). Unlike most programming languages, Bash array elements do not have to be the same data type — an array can contain both strings and numbers. Bash does not support multidimensional arrays.

Numerically indexed arrays can be accessed from the end using negative indices. The index -1 references the last element. Indices do not have to be contiguous.

Creating Arrays #

Numerically Indexed Arrays #

Bash variables are untyped, so any variable can be used as an indexed array without declaring it. To explicitly declare one, use the declare builtin:

declare -a array_name

You can assign elements individually by index:

array_name[0]=value_1
array_name[1]=value_2
array_name[2]=value_3

Or initialize the whole array at once using parentheses, with elements separated by spaces:

array_name=( element_1 element_2 element_3 )

When using this form, indexing starts at zero.

Associative Arrays #

Associative arrays use strings as keys instead of integers. Unlike indexed arrays, they must be declared before use:

declare -A array_name

Assign elements individually:

declare -A array_name

array_name[key_foo]=value_foo
array_name[key_bar]=value_bar
array_name[key_xyz]=value_xyz

Or use the inline form:

declare -A array_name=(
  [key_foo]=value_foo
  [key_bar]=value_bar
  [key_xyz]=value_xyz
)

Access Elements #

To reference a single element, use the following syntax:

${array_name[index]}

For example, to print the element at index 1:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

echo ${my_array[1]}

Helium

To access all elements, use @ or * as the index:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

echo "${my_array[@]}"

Hydrogen Helium Lithium Beryllium

The difference between @ and * matters when the expression is inside double quotes. "${my_array[*]}" expands to a single word with elements separated by spaces. "${my_array[@]}" expands each element as a separate word. Use @ when iterating over array elements to handle values that contain spaces correctly.

To print all keys (indices), add ! before the array name:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

echo "${!my_array[@]}"

0 1 2 3

Array Length #

To get the number of elements in an array, prefix the array name with #:

${#array_name[@]}

Here is an example:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

echo ${#my_array[@]}

4

Loop Through an Array #

The for loop is the most common way to iterate over array elements:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

for i in "${my_array[@]}"
do
  echo "$i"
done

Hydrogen
Helium
Lithium
Beryllium

To print both keys and values:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

for i in "${!my_array[@]}"
do
  echo "$i" "${my_array[$i]}"
done

0 Hydrogen
1 Helium
2 Lithium
3 Beryllium

You can also use a C-style loop with the array length:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

length=${#my_array[@]}

for (( i=0; i < ${length}; i++ ))
do
  echo $i ${my_array[$i]}
done

0 Hydrogen
1 Helium
2 Lithium
3 Beryllium

Add Elements #

To add an element at a specific index:

my_array[index]="New Element"

To append one or more elements without specifying an index, use the += operator:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

my_array+=( Cobalt Nickel )

echo "${my_array[@]}"

Hydrogen Helium Lithium Beryllium Cobalt Nickel

Slice an Array #

To extract a portion of an array, use the following syntax:

${array_name[@]:offset:length}

• offset — the starting index
• length — the number of elements to return

For example, to get two elements starting at index 1:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

echo "${my_array[@]:1:2}"

Helium Lithium

Delete Elements #

To remove a single element by index, use unset:

declare -a my_array=( "Hydrogen" "Helium" "Lithium" "Beryllium" )

unset my_array[2]

echo "${my_array[@]}"

Hydrogen Helium Beryllium

Note that unset removes the element but does not re-index the array. The index gap remains.

To delete the entire array:

unset my_array

Quick Reference #

For a printable quick reference, see the bash cheatsheet .

FAQ #

What is the difference between @ and * when accessing all elements?
Both expand to all array elements, but the behavior differs inside double quotes. "${arr[@]}" expands each element as a separate word, which correctly handles elements containing spaces. "${arr[*]}" expands to a single string with elements joined by the first character of IFS (usually a space). Always use @ when iterating.

How do I check if a Bash array is empty?
Check the length: [[ ${#my_array[@]} -eq 0 ]]. In a script:

if [[ ${#my_array[@]} -eq 0 ]]; then
  echo "Array is empty"
fi

How do I check if a value exists in an array?
Loop through the array and compare each element :

for i in "${my_array[@]}"; do
  [[ "$i" == "Helium" ]] && echo "Found" && break
done

Why does unset leave a gap in the array index?
unset arr[2] removes the element at index 2 but does not shift the remaining elements. The index 2 simply becomes unset. To re-index, reassign: arr=( "${arr[@]}" ).

Can Bash arrays hold arrays as elements?
No. Bash does not support nested or multidimensional arrays. To simulate a 2D structure, use naming conventions such as arr_0_0, arr_0_1, or use associative arrays with compound keys like arr[0,1].

Conclusion #

Bash arrays store multiple values in a single variable. Use indexed arrays for ordered lists and associative arrays for key-value pairs. The [@] expansion, ${#arr[@]} for length, += for appending, and unset for deletion are the core operations you will use most often.

For more on Bash scripting, see the guides on for loops and if/else statements .

If you have any questions, feel free to leave a comment below.

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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