Master Bash Arrays: Declaration, Access, Looping, and Real-World Uses

Introduction

Bash arrays store multiple values in a single variable, enabling efficient handling of lists, batch file operations, and numeric calculations.

Declaring and Initializing Arrays

Two common approaches are supported:

Using parentheses to assign values directly:

# Declare and initialize an array
myArray=(value1 value2 value3)

Using declare -a and then assigning each index:

# Declare an empty indexed array
declare -a myArray
myArray[0]="value1"
myArray[1]="value2"
myArray[2]="value3"

Accessing Elements

Array elements are accessed by a zero‑based index:

#!/bin/bash
myArray=("apple" "banana" "cherry")
echo "First element: ${myArray[0]}"
echo "Second element: ${myArray[1]}"
echo "Third element: ${myArray[2]}"

Modifying Elements

Assign a new value to a specific index to replace an element:

#!/bin/bash
myArray=("apple" "banana" "cherry")
myArray[1]="blueberry"
echo "Modified array: ${myArray[@]}"

Iterating Over an Array

A for loop can traverse all elements:

#!/bin/bash
myArray=("apple" "banana" "cherry")
for element in "${myArray[@]}"; do
    echo "$element"
done

Getting Array Length

The expression ${#myArray[@]} returns the number of elements:

#!/bin/bash
myArray=("apple" "banana" "cherry")
length=${#myArray[@]}
echo "Array length: $length"

Removing Elements

Use unset to delete a single element or the entire array:

#!/bin/bash
myArray=("apple" "banana" "cherry")
# Delete the second element (index 1)
unset myArray[1]
echo "After deletion: ${myArray[@]}"
# Delete the whole array
unset myArray

Practical Applications

File List Processing

Collect all files in the current directory and iterate over them:

#!/bin/bash
files=(* )
for file in "${files[@]}"; do
    echo "$file"
done

Argument Passing

Store command‑line arguments in an array and process each one:

#!/bin/bash
args=("$@")
for arg in "${args[@]}"; do
    echo "$arg"
done

Numeric Computation

Sum the values of a numeric array using arithmetic expansion:

#!/bin/bash
numbers=(1 2 3 4 5)
sum=0
for number in "${numbers[@]}"; do
    sum=$((sum + number))
done
echo "Sum: $sum"

Conclusion

Arrays are a fundamental data structure in Bash scripting. Mastering declaration, initialization, element access, modification, iteration, length retrieval, and element removal enables the creation of flexible, maintainable scripts for a wide range of automation tasks.