Array Basics

Arrays let you store multiple values in a single variable. They're essential for handling lists of files, arguments, or any collection of data.

Creating Arrays

#!/bin/bash

# Method 1: Parentheses
FRUITS=("apple" "banana" "cherry")

# Method 2: Individual assignment
COLORS[0]="red"
COLORS[1]="green"
COLORS[2]="blue"

# Method 3: Using declare
declare -a NUMBERS=(1 2 3 4 5)

Accessing Elements

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

# Single element (0-indexed)
echo "${FRUITS[0]}"    # apple
echo "${FRUITS[1]}"    # banana
echo "${FRUITS[-1]}"   # date (last element)

# All elements
echo "${FRUITS[@]}"    # apple banana cherry date
echo "${FRUITS[*]}"    # apple banana cherry date

Array Length

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

# Number of elements
echo "${#FRUITS[@]}"   # 3

# Length of specific element
echo "${#FRUITS[0]}"   # 5 (length of "apple")

Exercise: Create and Access Array

Work with array elements:

Looping Over Arrays

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

# Loop over values
for fruit in "${FRUITS[@]}"; do
    echo "Fruit: $fruit"
done

# Loop with indices
for i in "${!FRUITS[@]}"; do
    echo "$i: ${FRUITS[$i]}"
done

Adding Elements

#!/bin/bash
FRUITS=("apple" "banana")

# Append one element
FRUITS+=("cherry")

# Append multiple
FRUITS+=("date" "elderberry")

# Insert at specific index
FRUITS[10]="fig"    # Creates sparse array

echo "${FRUITS[@]}"
echo "Length: ${#FRUITS[@]}"

Removing Elements

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

# Remove by index
unset 'FRUITS[1]'    # Removes "banana"
echo "${FRUITS[@]}"   # apple cherry date

# Note: This creates a sparse array!
echo "${FRUITS[1]}"   # empty
echo "${FRUITS[2]}"   # cherry

# To reindex after deletion
FRUITS=("${FRUITS[@]}")

Exercise: Loop Over Array

Iterate through an array:

Array Slicing

#!/bin/bash
NUMS=(0 1 2 3 4 5 6 7 8 9)

# Slice: ${array[@]:start:count}
echo "${NUMS[@]:3:4}"     # 3 4 5 6
echo "${NUMS[@]:5}"       # 5 6 7 8 9 (from index 5)
echo "${NUMS[@]: -3}"     # 7 8 9 (last 3)

Copying Arrays

#!/bin/bash
ORIGINAL=(1 2 3 4 5)

# Copy entire array
COPY=("${ORIGINAL[@]}")

# Modify copy (doesn't affect original)
COPY[0]=99
echo "${ORIGINAL[0]}"   # 1
echo "${COPY[0]}"       # 99

Array from Command Output

#!/bin/bash
# Array from command output
FILES=($(ls *.txt))

# Better: handle spaces in filenames
while IFS= read -r -d '' file; do
    FILES+=("$file")
done < <(find . -name "*.txt" -print0)

Checking if Array Contains Element

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

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

if contains "banana" "${FRUITS[@]}"; then
    echo "Found banana!"
fi

Key Takeaways

• Create arrays with ARR=(item1 item2 item3)
• Access elements with ${ARR[index]} (0-indexed)
• Get all elements with "${ARR[@]}"
• Get length with ${#ARR[@]}
• Append with ARR+=(new_item)
• Loop with for item in "${ARR[@]}"
• Always quote: "${ARR[@]}" to handle spaces
• Use ${!ARR[@]} to get indices