Shell by Example: Arrays

Shell by Example: Arrays Bash

	`#!/bin/bash`
Arrays in Bash let you store multiple values in a single variable. Note: Arrays are a Bash feature and are not available in POSIX sh.
Create an array with parentheses.	`fruits=("apple" "banana" "cherry" "date")`
Access elements using index (0-based).	`echo "First fruit: ${fruits[0]}" echo "Second fruit: ${fruits[1]}"`
Get all elements with [@] or [*].	`echo "All fruits: ${fruits[@]}"`
Get the number of elements.	`echo "Number of fruits: ${#fruits[@]}"`
Add an element to the end.	`fruits+=("elderberry") echo "After adding: ${fruits[@]}"`
Set a specific index.	`fruits[1]="blueberry" echo "After replacing: ${fruits[@]}"`
Loop over array elements.	`echo "Iterating over fruits:" for fruit in "${fruits[@]}"; do echo " - $fruit" done`
Loop with indices.	`echo "With indices:" for i in "${!fruits[@]}"; do echo " [$i] = ${fruits[$i]}" done`
Array slicing: ${array[@]:start:length}	`echo "First three: ${fruits[@]:0:3}" echo "From index 2: ${fruits[@]:2}"`
Get array indices.	`echo "Indices: ${!fruits[@]}"`
Check if array is empty.	`empty_array=() if [ ${#empty_array[@]} -eq 0 ]; then echo "Array is empty" fi`
Create array from command output.	`files=($(ls *.sh 2>/dev/null)) echo "Shell files: ${files[@]}"`
Delete an element (leaves a gap in indices).	`unset 'fruits[2]' echo "After unset [2]: ${fruits[@]}" echo "Indices now: ${!fruits[@]}"`
Bash 4+ Bash 4+ provides associative arrays (hash maps) using `declare -A`:	`declare -A user user[name]="Alice" user[email]="alice@example.com" user[age]="30" echo "Name: ${user[name]}" echo "Email: ${user[email]}"`
Iterate over associative array keys:	`for key in "${!user[@]}"; do echo "$key: ${user[$key]}" done`
Check if a key exists:	`if [[ -v user[name] ]]; then echo "name key exists" fi`
Bash 4+ provides `mapfile` (or `readarray`) to read lines from a file or command into an array:	`mapfile -t lines < /etc/passwd`
Read only first 5 lines:	`mapfile -t -n 5 lines < /etc/passwd`
Read from a command using process substitution:	`mapfile -t users < <(cut -d: -f1 /etc/passwd \| head -5) echo "Users: ${users[@]}"`
Read with a specific delimiter:	`mapfile -t -d ':' fields <<< "a:b:c:d"`

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