Section 5: Advanced Shell Scripting Concepts

Lesson 1: Handling Signals and Traps

Handling signals and traps in shell scripts allows for graceful response to events such as interruptions and errors.

1.1 Responding to Signals 

#!/bin/bash

# Handling signals in shell scripts

# Define a function to handle the interrupt signal (Ctrl+C)

handle_interrupt() {

    echo "Script interrupted. Cleaning up..."

    # Additional cleanup tasks

    exit 1

}

# Register the function to handle the interrupt signal

trap 'handle_interrupt' INT

# Main script logic

echo "Running script. Press Ctrl+C to interrupt."

while true; do

    # Main script tasks

    sleep 1

done

1.2 Using Traps for Signal Handling

#!/bin/bash

# Using traps for signal handling

# Define a function to handle the exit signal

handle_exit() {

    echo "Script is exiting. Performing cleanup..."

    # Additional cleanup tasks

}

# Register the function to handle the exit signal

trap 'handle_exit' EXIT

# Main script logic

echo "Running script. This will perform cleanup on exit."

# Main script tasks

sleep 3

Lesson 2: Regular Expressions in Shell Scripts

Regular expressions (regex) are powerful tools for pattern matching and text manipulation in shell scripts.

2.1 Pattern Matching with grep 

#!/bin/bash

# Pattern matching with grep

# Search for lines containing "error" in a file

grep "error" logfile.txt

# Search for lines starting with "warning"

grep "^warning" logfile.txt

2.2 Text Manipulation Using sed

#!/bin/bash

# Text manipulation using sed

# Replace "apple" with "orange" in a file

sed -i 's/apple/orange/g' fruits.txt

# Delete lines containing "banana"

sed -i '/banana/d' fruits.txt

Understanding how to handle signals gracefully and utilize regular expressions for text manipulation enhances the capabilities of shell scripts. In the next sections, we'll explore more advanced scripting techniques and real-world applications.