Array

Define an indexed array by listing elements inside parentheses, separated by spaces.

arr=(element1 element2 element3)

You can also assign elements individually by specifying an index.

arr[0]=element1
arr[1]=element2

To define an associative array, first declare it with declare -A, then assign key-value pairs.

declare -A assoc
assoc[key]=value

Reference a specific element with ${arr[index]}. Expand all elements with ${arr[@]} or ${arr[*]}.

${arr[0]}               # Element at index 0
${arr[@]}               # All elements (each as a separate argument)
${arr[*]}               # All elements (as one IFS-joined string)
${#arr[@]}              # Number of elements
${!arr[@]}              # All indices (keys)
${arr[@]:start:length}  # Slice: length elements starting at start

Append elements with +=. Remove an element with unset.

arr+=(new_element)        # Append to the end
unset arr[index]          # Delete the element at the given index

A basic example of defining an indexed array and referencing its elements. A list of jujutsu sorcerers is stored in an array.

members=("Gojo Satoru" "Itadori Yuji" "Fushiguro Megumi" "Kugisaki Nobara")
echo ${members[0]}
echo ${members[2]}
echo ${#members[@]}
Gojo Satoru
Fushiguro Megumi
4

To iterate over all elements, use ${arr[@]} inside double quotes.

jujutsu_members.sh

#!/bin/bash

members=("Gojo Satoru" "Itadori Yuji" "Fushiguro Megumi" "Kugisaki Nobara" "Ryomen Sukuna")

for member in "${members[@]}"; do
    echo "Member: $member"
done

bash jujutsu_members.sh
Member: Gojo Satoru
Member: Itadori Yuji
Member: Fushiguro Megumi
Member: Kugisaki Nobara
Member: Ryomen Sukuna

An example of declaring an associative array with declare -A and mapping sorcerer names to their affiliations.

domain_expansion.sh

#!/bin/bash

declare -A affiliation

affiliation["Gojo Satoru"]="Jujutsu High"
affiliation["Ryomen Sukuna"]="King of Curses"
affiliation["Itadori Yuji"]="Jujutsu High"

for key in "${!affiliation[@]}"; do
    echo "$key => ${affiliation[$key]}"
done

bash domain_expansion.sh
Itadori Yuji => Jujutsu High
Ryomen Sukuna => King of Curses
Gojo Satoru => Jujutsu High

Appending and deleting elements. Use += to append and unset to delete.

techniques=("Infinity" "Divergent Fist" "Boogie Woogie")
techniques+=("Straw Doll")
echo ${techniques[@]}
unset techniques[1]
echo ${techniques[@]}
echo ${#techniques[@]}
Infinity Divergent Fist Boogie Woogie Straw Doll
Infinity Boogie Woogie Straw Doll
3

Use a slice to extract a portion of an array. ${arr[@]:start:length} returns length elements starting from index start.

cursed=("Infinity" "Black Flash" "Hollow Purple" "Mahoraga" "Straw Doll")
echo ${cursed[@]:1:3}
Black Flash Hollow Purple Mahoraga

mission_log.sh

#!/bin/bash
# Mission log processing script

declare -A email
email["Gojo Satoru"]="gojo@example.com"
email["Itadori Yuji"]="itadori@example.com"
email["Fushiguro Megumi"]="fushiguro@example.com"
email["Kugisaki Nobara"]="kugisaki@example.com"
email["Ryomen Sukuna"]="sukuna@example.com"

missions=("Detention Center" "Juvenile Reformatory" "Shibuya Incident" "Culling Game")

echo "=== Mission List ==="
for i in "${!missions[@]}"; do
    echo "[$i] ${missions[$i]}"
done

echo ""
echo "=== Member Contacts ==="
for name in "${!email[@]}"; do
    echo "$name: ${email[$name]}"
done

echo ""
echo "Recent missions: ${missions[@]:1:2}"

Both ${arr[@]} and ${arr[*]} expand all elements, but they behave differently inside double quotes. "${arr[@]}" expands each element as a separate argument, so elements containing spaces are not split. "${arr[*]}" joins all elements into a single string using the IFS separator (a space by default). In loops and function calls, always use "${arr[@]}".

Deleting an element with unset does not reindex the array. If you delete index 1, the remaining indices are 0, 2, 3, ... with a gap. ${#arr[@]} returns the actual element count, which may not equal the highest index. To compact the indices, reassign with arr=("${arr[@]}").

Bash arrays are one-dimensional only — multidimensional arrays are not natively supported. Common workarounds include using naming conventions like matrix_1_2 for multiple variables, or encoding data as delimited strings.

Common Mistake 1: Elements with spaces are split without quotes

Omitting double quotes when expanding an array causes the shell to split elements on whitespace, breaking multi-word values into separate arguments.

techniques=("Hollow Purple" "Black Flash" "Divergent Fist")
for t in ${techniques[@]}; do
    echo "$t"
done
Hollow
Purple
Black
Flash
Divergent
Fist

Without quotes, ${techniques[@]} is split on whitespace, producing six tokens instead of three. Wrapping the expansion in double quotes preserves each element as a single unit.

for t in "${techniques[@]}"; do
    echo "$t"
done
Hollow Purple
Black Flash
Divergent Fist

Common Mistake 2: Forgetting declare -A for associative arrays

If you use string keys without first declaring the array with declare -A, Bash treats it as an indexed array. String keys are converted to the number 0, so each assignment overwrites the same slot and only the last value survives.

affiliation["Gojo Satoru"]="Jujutsu High"
affiliation["Ryomen Sukuna"]="King of Curses"
affiliation["Itadori Yuji"]="Jujutsu High"
echo ${affiliation[@]}
Jujutsu High

Three assignments were made, but only one value remains. Adding declare -A at the top fixes the problem.

declare -A affiliation
affiliation["Gojo Satoru"]="Jujutsu High"
affiliation["Ryomen Sukuna"]="King of Curses"
affiliation["Itadori Yuji"]="Jujutsu High"
echo ${#affiliation[@]}
3