Section 3: Functions and Modularization

Lesson 1: Defining Functions in Shell Scripts

Functions in shell scripts provide a way to create reusable code blocks and enhance modularization.

1.1 Creating Reusable Code Blocks 

#!/bin/bash

# Defining functions in shell scripts

# Function definition

greet_user() {

    echo "Hello, $1!"

}

# Calling the function

greet_user "John"

1.2 Passing Arguments to Functions 

#!/bin/bash

# Passing arguments to functions

# Function definition

multiply_numbers() {

    result=$(( $1 * $2 ))

    echo "The result of multiplication is: $result"

}

# Calling the function

multiply_numbers 5 3

Lesson 2: Scope of Variables

Understanding the scope of variables, both local and global, is crucial in shell scripting.

2.1 Local Variables

#!/bin/bash

# Local variables in shell scripts

# Function definition

print_local_variable() {

    local localVar="I am a local variable"

    echo "$localVar"

}

# Calling the function

print_local_variable

# Attempting to access the local variable outside the function (will result in an error)

echo "$localVar"

2.2 Global Variables 

#!/bin/bash

# Global variables in shell scripts

# Declaring a global variable

globalVar="I am a global variable"

# Function definition

print_global_variable() {

    echo "$globalVar"

}

# Calling the function

print_global_variable

2.3 Returning Values from Functions 

#!/bin/bash

# Returning values from functions

# Function definition

add_numbers() {

    local result=$(( $1 + $2 ))

    echo "$result"

}

# Calling the function and storing the result in a variable

sum=$(add_numbers 8 4)

echo "The sum is: $sum"

Understanding functions and variable scope is essential for creating well-organized and maintainable shell scripts. In the upcoming sections, we'll explore more advanced scripting techniques and real-world applications.