Advanced Linux shell scripting for DevOps engineers

As a DevOps engineer, the ability to write efficient and powerful shell scripts is paramount, as it allows you to automate tasks, manage systems, and streamline processes, all while promoting collaboration between development and operations teams.

Table of Contents:

1. Understanding the Fundamentals 🌟

   • What is a Shell Script?

   • Choosing the Right Shell: Bash, Zsh, or Others?

   • Executing Shell Scripts: Shebang, Permissions, and Running Scripts.

2. Working with Variables and Data 💻

   • Declaring and Assigning Variables

   • Special Variables: $0, $#, $*, $@, $?, and $$

   • Command Substitution and Arithmetic Operations

3. Conditional Statements and Control Structures 🔍

   • If-Else Statements

   • Case Statements

   • Looping with For and While

4. File and Directory Handling 📂

   • Reading and Writing Files

   • Text Processing with Sed and Awk

   • Managing Directories: Creating, Listing, and Deleting

5. Advanced Text Processing 📝

   • Regular Expressions and Pattern Matching

   • Grepping, Cutting, Sorting, and Unique Filters

   • Combining Tools: Pipes and Redirections

6. Working with Functions 🛠️

   • Declaring and Using Functions

   • Local and Global Variables

   • Recursion and Function Libraries

7. Process Management and Job Control 🔄

   • Process IDs (PIDs) and Signals

   • Background and Foreground Processes

   • Managing Jobs with bg, fg, and Jobs Command

8. Handling Errors and Debugging 🐞

   • Exit Status and Return Codes

   • Trapping Signals and Errors

   • Debugging Techniques: Echo, set -x, and set -e

9. Interacting with the System 🖥️

   • Environment Variables

   • System Information: uname, df, free, and top

   • Working with Date and Time

10. Shell Scripting Best Practices 📌

    • Code Readability and Maintainability

    • Error Handling and Logging

    • Optimizing Shell Scripts: Performance Tips

11. Automating DevOps Tasks 🔄🔧

    • Building Deployment Scripts

    • Continuous Integration (CI) Pipelines

    • Configuration Management with Shell Scripts3

Example

**

Shell Script: Using Loops or Commands with Start Day and End Day Variables using Arguments** 🐚🔄

#!/bin/bash

if [ $# -ne 2 ]; then

echo "Usage: $0 <start_day> <end_day>"

exit 1

fi

for (( day = $1; day <= $2; day++ )); do

echo "Day $day"

done

Create a Script to backup all your work done till now.

#!/bin/bash

#Define the backup directory and filename

backup_dir="/path/to/backup" # Replace with your desired backup directory backup_filename="backup_$(date +%Y%m%d%H%M%S).tar.gz"

#Create the backup directory if it doesn't exist

mkdir -p "$backup_dir"

#Compress and backup the files

tar -czf "$backup_dir/$backup_filename" /path/to/work/done/till/now # Replace with the directory containing your work

echo "Backup created successfully: $backup_dir/$backup_filename"

Cron and Crontab, to automate the backup Script

backup_script.sh

#!/bin/bash

#Define the backup directory and filename

backup_dir="/path/to/backup" # Replace with your desired backup directory backup_filename="backup_$(date +%Y%m%d%H%M%S).tar.gz"

#Create the backup directory if it doesn't exist

mkdir -p "$backup_dir"

#Compress and backup the files

tar -czf "$backup_dir/$backup_filename" /path/to/work/done/till/now # Replace with the directory containing your work

echo "Backup created successfully: $backup_dir/$backup_filename"

Cron

#!/bin/bash

#Absolute path to the backup_script.sh

backup_script="/path/to/backup_script.sh" # Replace with the actual path to backup_script.sh

(crontab -l ; echo "0 2 * $backup_script") | crontab -

echo "Backup job has been scheduled to run daily at 2:00 AM."