Array Operations in Linux bash

Bash scripts are one of the most convenient approaches for automating command line processes. They help us perform multiple operations in a simpler and more understandable manner, allowing us to accomplish tasks similar to other programming languages. Arrays in bash provide a powerful way to store and manipulate collections of data elements.

The syntax of bash can be tricky at first, but this tutorial will explain the essential array operations step by step. We'll explore how to create, access, and manipulate arrays using practical examples that you can run directly in your terminal.

How to Create and Execute a Bash File

The first step when working with bash scripts is creating one. On Linux or macOS machines, create a bash file using the following command

touch mybashfile.sh

The filename can be anything you desire, but the .sh extension is conventional for shell scripts. Once you save the file, execute it with the following command

bash mybashfile.sh

Alternatively, you can make the file executable and run it directly

chmod +x mybashfile.sh
./mybashfile.sh

Creating Arrays in Bash

Bash arrays can be created in several ways. The most common method is using parentheses with space-separated elements

#!/bin/bash

# Method 1: Direct assignment
myarray=(apple banana mango kiwi litchi watermelon)

# Method 2: Individual element assignment
fruits[0]="apple"
fruits[1]="banana"
fruits[2]="mango"

# Method 3: Using declare
declare -a colors=("red" "green" "blue")

Accessing Array Elements

Printing the First Element

To access the first element of an array, use index 0

#!/bin/bash

myarray=(apple banana mango kiwi litchi watermelon)

# Printing the first element
echo ${myarray[0]}
echo "First fruit: ${myarray[0]}"

When you run this script, it produces the following output

apple
First fruit: apple

Printing All Elements

Use [@] or [*] to access all array elements

#!/bin/bash

myarray=(apple banana mango kiwi litchi watermelon)

# Printing all array elements
echo "All fruits: ${myarray[@]}"
echo "Using asterisk: ${myarray[*]}"

Output

All fruits: apple banana mango kiwi litchi watermelon
Using asterisk: apple banana mango kiwi litchi watermelon

Printing Elements in a Range

Use slice notation ${array[@]:start:length} to extract a range of elements

#!/bin/bash

myarray=(apple banana mango kiwi litchi watermelon)

# Printing array elements in specific ranges
echo "Elements 1-3: ${myarray[@]:1:3}"
echo "Elements 2-end: ${myarray[@]:2}"
echo "Last 2 elements: ${myarray[@]: -2}"

Output

Elements 1-3: banana mango kiwi
Elements 2-end: mango kiwi litchi watermelon
Last 2 elements: litchi watermelon

Array Properties and Operations

Getting Array Length

Use # operator to get the number of elements

#!/bin/bash

myarray=(apple banana mango kiwi litchi watermelon)

# Printing the number of elements
echo "Array length: ${#myarray[@]}"
echo "Alternative syntax: ${#myarray[*]}"

Output

Array length: 6
Alternative syntax: 6

Adding and Removing Elements

#!/bin/bash

fruits=(apple banana mango)

# Adding elements
fruits+=(kiwi litchi)  # Append multiple elements
fruits[10]=watermelon  # Add at specific index

# Removing elements
unset fruits[1]  # Remove banana
unset fruits     # Remove entire array

echo "Modified array: ${fruits[@]}"
echo "Array length: ${#fruits[@]}"

Practical Array Operations

Iterating Through Arrays

#!/bin/bash

fruits=(apple banana mango kiwi)

# Method 1: Iterate over elements
for fruit in "${fruits[@]}"; do
    echo "Fruit: $fruit"
done

# Method 2: Iterate using indices
for i in "${!fruits[@]}"; do
    echo "fruits[$i] = ${fruits[i]}"
done

Conclusion

Bash arrays provide powerful capabilities for storing and manipulating collections of data. Understanding array operations like accessing elements, slicing, and iteration is essential for effective bash scripting. These operations form the foundation for more complex data processing tasks in shell scripts.