advanced-array-patterns

CRITICAL GUIDELINES

Windows File Path Requirements

MANDATORY: Always Use Backslashes on Windows for File Paths

When using Edit or Write tools on Windows, you MUST use backslashes (\) in file paths, NOT forward slashes (/).

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Advanced Bash Array Patterns (2025)

Overview

Comprehensive guide to bash arrays including indexed arrays, associative arrays, mapfile/readarray, and advanced manipulation patterns following 2025 best practices.

Indexed Arrays

Declaration and Initialization

#!/usr/bin/env bash
set -euo pipefail

# Method 1: Direct assignment
files=("file1.txt" "file2.txt" "file with spaces.txt")

# Method 2: Compound assignment
declare -a numbers=(1 2 3 4 5)

# Method 3: Individual assignment
fruits[0]="apple"
fruits[1]="banana"
fruits[2]="cherry"

# Method 4: From command output (CAREFUL with word splitting)
# ✗ DANGEROUS - splits on spaces
files_bad=$(ls)

# ✓ SAFE - preserves filenames with spaces
mapfile -t files_good < <(find . -name "*.txt")

# Method 5: Brace expansion
numbers=({1..100})
letters=({a..z})

Array Operations

#!/usr/bin/env bash
set -euo pipefail

arr=("first" "second" "third" "fourth" "fifth")

# Length
echo "Length: ${#arr[@]}"  # 5

# Access elements
echo "First: ${arr[0]}"
echo "Last: ${arr[-1]}"  # Bash 4.3+
echo "Second to last: ${arr[-2]}"

# All elements (properly quoted for spaces)
for item in "${arr[@]}"; do
    echo "Item: $item"
done

# All indices
for idx in "${!arr[@]}"; do
    echo "Index $idx: ${arr[$idx]}"
done

# Slice (offset:length)
echo "${arr[@]:1:3}"  # second third fourth

# Slice from offset to end
echo "${arr[@]:2}"  # third fourth fifth

# Append element
arr+=("sixth")

# Insert at position (complex)
arr=("${arr[@]:0:2}" "inserted" "${arr[@]:2}")

# Remove element by index
unset 'arr[2]'

# Remove by value (all occurrences)
arr_new=()
for item in "${arr[@]}"; do
    [[ "$item" != "second" ]] && arr_new+=("$item")
done
arr=("${arr_new[@]}")

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

# Check if element exists
contains() {
    local needle="$1"
    shift
    local item
    for item in "$@"; do
        [[ "$item" == "$needle" ]] && return 0
    done
    return 1
}

if contains "third" "${arr[@]}"; then
    echo "Found 'third'"
fi