Section 6: Error Handling and Debugging

Lesson 1: Error Handling in Shell Scripts

Effective error handling in shell scripts involves using traps for specific signals, managing exit codes, and providing meaningful error messages.

1.1 Using Trap for Error Handling 

#!/bin/bash

# Error handling with trap

# Define a function to handle errors

handle_error() {

    echo "Error occurred. Exiting script."

    exit 1

}

# Register the function to handle errors

trap 'handle_error' ERR

# Main script logic

echo "Running script with potential errors."

# Simulate an error (e.g., division by zero)

result=$(echo 1/0)

echo "Result: $result"

1.2 Exit Codes and Error Messages 

#!/bin/bash

# Exit codes and error messages

# Function to perform a task with potential errors

perform_task() {

    # Simulate an error condition

    if [ "$1" -eq 0 ]; then

        echo "Error: Division by zero."

        exit 1

    fi

}

# Main script logic

echo "Running script with exit codes."

# Call the function with an argument

perform_task 0

# Check the exit code and display an error message if needed

if [ $? -ne 0 ]; then

    echo "Error: Task failed."

fi

Lesson 2: Debugging Shell Scripts

Debugging shell scripts involves adding debug statements, analyzing variable values, and using tools like set -x for script debugging.

2.1 Adding Debug Statements 

#!/bin/bash

# Adding debug statements

# Enable debug mode

set -e

# Main script logic with debug statements

echo "Starting script execution."

# Debug statement 1

echo "Debug: Performing task 1."

# Debug statement 2

echo "Debug: Performing task 2."

# Debug statement 3

echo "Debug: Performing task 3."

# Disable debug mode

set +e

echo "Script execution completed successfully."

2.2 Using set -x for Script Debugging

#!/bin/bash

# Using set -x for script debugging

# Enable debugging

set -x

# Main script logic

echo "Starting script execution."

# Debug statement 1

echo "Debug: Performing task 1."

# Debug statement 2

echo "Debug: Performing task 2."

# Debug statement 3

echo "Debug: Performing task 3."

# Disable debugging

set +x

echo "Script execution completed successfully."

Understanding error handling techniques and incorporating debugging practices improves the reliability and maintainability of shell scripts. In the upcoming sections, we'll explore more advanced scripting techniques and real-world applications.