Shell Scripting for DevOps | Shell Scripting Zero 2 Hero

Shell Scripting Day - 1 :

Introduction

• Shell scripting is used for automating day-to-day activities on a Linux computer.

• It is useful for devops engineers to reduce manual work and increase efficiency.

Basics of Shell Scripting

• Shell scripting is a process of automating regular activities on a Linux computer.

• To write a shell script, you need to create a file with a .sh extension using the touch command or a text editor like Vim.

• The first line of the shell script should start with #! followed by the path to the shell interpreter, such as #!/bin/bash.

• Comments in shell scripting start with #.

  Basic Commands

  • ls: lists the files and directories in the current directory.

  • ls -ltr: lists the files and directories in the current directory in long format, sorted by modification time (oldest first).

  • touch: creates a new empty file or updates the modification time of an existing file.

  • man: displays the manual page for a command.

  • cat: concatenates and displays the contents of a file.

  • echo: prints the given text or variable to the standard output.

  • pwd: prints the path of the current directory.

  • cd: changes the current directory.

  • mkdir: creates a new directory.

  • rm: removes a file or directory.

  • chmod: changes the permissions of a file or directory.

Creating a Simple Shell Script

• To create a simple shell script, you can use the following template:

We then wrote a simple shell script that creates a directory and two files inside that directory. The script is as follows:

#!/bin/bash

# Create a directory
mkdir Pratik

# Go inside the directory
cd Pratik

# Create two files
touch firstfile
touch secondfile

Overall, shell scripting is a powerful tool for devops engineers and other Linux users who want to automate their work and increase efficiency. By learning the basics and practicing with simple and advanced scripts, you can become proficient in shell scripting and improve your productivity.

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Shell Scripting Day - 2 :

Notes for Advanced Shell Scripting Concepts by Pratik Gote

• Introduction

  • Welcome back to the Article

  • Focusing on advanced shell scripting concepts

• Today's Topic: Custom Node Script to Detect Node Health

  • Writing a shell script called node_health.sh

  • Using DF -h, free -g, and nproc commands to output different parameters on the virtual machine

1 : Metadata Information:

• Always provide metadata information at the beginning of the script.

• Example:

    #!/bin/bash
    #
    # This script outputs the node health
    #
    # Author: Pratik
    # Date: 1st December
    # Purpose: Outputs the node health
    # Version: V1
  

2 : Debug Mode:

• Use set -x to print the script in debug mode.

• Example:

    #!/bin/bash
    set -x
  

3 : Find Processes:

• Use ps -ef to print all the processes that are running on the virtual machine.

• Example:

    ps -ef
  

4 : Filter Output:

• Use grep to filter the output of any command.

• Example:

  
    ps -ef | grep Amazon
  

5 : Get Process IDs:

• Use awk to get the specific column from the output.

• Example:

    ps -ef | grep Amazon | awk '{print $2}'
  

6 : Pipe Command:

• Use | to get the output of the first command and send it to the second command.

• Example:

    ps -ef | grep Amazon | awk '{print $2}'
  

7 : Exit Script on Error:

• Use set -e to exit the script when there is an error.

• Example:

    #!/bin/bash
    set -e
  

8 : Pipe Fail:

• Use set -o pipefail to exit the script when there is a pipe failure.

• Example:

    #!/bin/bash
    set -e
    set -o pipefail
  

9 : Log Files:

• Use curl to retrieve the log files from the internet.

• Example:

    curl https://raw.githubusercontent.com/username/repository/main/logfile.log
  

10 : Download Files:

• Use wget to download the files from the internet.

• Example:

    wget https://raw.githubusercontent.com/username/repository/main/logfile.log
  

11 : Find Command:

• Use find to search for files in the file system.

• Example:

    find / -name "logfile.log"
  

12 : If Loops, Else Loops, and For Loops:

• Use if, else, and for to write conditional statements and loops in the script.

• Example:

    if [ condition ]; then
        command
    elif [ condition ]; then
        command
    else
        command
    fi
  
    for i in $(ls); do
        command
    done
  

overall Shell commands :

#!/bin/bash

# Metadata Information
Author: Abhishek
Date: 1st December
Prerequisites: None
Purpose: This script executes and outputs the node health
Version: V1

set -x
set -e
set -o pipefail

ps -ef | grep node | awk '{print $2}'

df -h
free -h
nproc

top

if [ $(ps -ef | grep node | awk '{print $2}') -gt 0 ]; then
    echo "Node is running"
else
    echo "Node is not running"
fi

curl https://example.com

wget https://example.com/file.txt

find / -name file.txt


# Checking if a Process is Running with if-else
if [ $(ps -ef | grep node | awk '{print $2}') -gt 0 ]; then
    echo "Node is running"
else
    echo "Node is not running"
fi

# Monitoring Disk Space Usage with if-else

if [ $(df -h | awk '{print $5}' | sed '/%//g') -gt 80 ]; then
    echo "Disk space is low"
else
    echo "Disk space is okay"
fi

for i in {1..5}; do
    echo "Iteration $i"
done

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Shell Scripting & Linux Interview Questions for DevOps Engineers

Here are the common interview questions, along with some additional questions that are commonly asked in shell scripting interviews:

Shell Scripting Interview Questions

Basic Questions

1. What is shell scripting?

   • Answer: Shell scripting is a way to automate tasks on a Linux or Unix system by writing a series of commands in a file that can be executed by the shell.

2. What are the advantages of shell scripting?

   • Answer: Shell scripting allows for automation, increased productivity, and ease of maintenance.

3. What are the different types of shell scripts?

   • Answer: There are two types of shell scripts: Bourne shell scripts (sh) and Bash shell scripts (bash).

4. What is bash?

   • Answer: Bash is a type of programming language that you use in the terminal (the command line) on most Linux systems and MacOS. It allows you to write scripts, which are just files with a series of commands. These scripts can do complicated tasks, like making backups of your files, by running several commands automatically. This makes it easier to manage and automate tasks on your computer.

Scripting Questions

1. Write a script to print "Hello World"?

   • Answer: echo "Hello World"

2. How do you declare a variable in shell scripting?

   • Answer: variable_name=value

3. What is the difference between= and == in shell scripting?

   • Answer: = is used for assignment, while == is used for comparison.

4. How do you concatenate strings in shell scripting?

   • Answer: Using the + operator or by using the ${parameter} syntax.

5. What is the purpose of theif statement in shell scripting?

   • Answer: To execute a block of code if a condition is true.

6. How do you use thefor loop in shell scripting?

   • Answer: for variable in list; do command; done

7. What is the purpose of thewhile loop in shell scripting?

   • Answer: To execute a block of code as long as a condition is true.

8. How do you use thecase statement in shell scripting?

   • Answer: case variable in pattern1) command1;; pattern2) command2;; esac

File and Directory Management Questions

1. How do you create a new directory in shell scripting?

   • Answer: mkdir directory_name

2. How do you delete a file in shell scripting?

   • Answer: rm file_name

3. How do you copy a file in shell scripting?

   • Answer: cp source_file destination_file

4. How do you move a file in shell scripting?

   • Answer: mv source_file destination_file

5. How do you check if a file exists in shell scripting?

   • Answer: if [ -f file_name ]; then echo "File exists"; fi

Error Handling and Debugging Questions

1. How do you handle errors in shell scripting?

   • Answer: Using the trap command or by checking the exit status of commands.

2. How do you debug a shell script?

   • Answer: Using the -x option or by adding echo statements to the script.

Advanced Questions

1. How do you use regular expressions in shell scripting?

   • Answer: Using the grep command or by using the =~ operator.

2. How do you use arrays in shell scripting?

   • Answer: Declaring an array using array_name=() and accessing elements using ${array_name[index]}.

3. How do you use functions in shell scripting?

   • Answer: Declaring a function using function_name() { command; } and calling it using function_name.

Common Interview Questions

1. Can you explain the difference betweensh and bash?

   • Answer: sh is the Bourne shell, while bash is the Bourne-Again SHell.

2. How do you schedule a script to run at a specific time?

   • Answer: Using the cron command.

3. How do you make a script executable?

   • Answer: Using the chmod command to set the execute permission.

4. Can you explain the concept of shell expansion?

   • Answer: Shell expansion is the process of replacing special characters and expressions with their values.

5. How do you use shell scripting to automate system administration tasks?

   • Answer: By writing scripts to perform tasks such as backups, user management, and system monitoring.

conclusion :

shell scripting is crucial for DevOps engineers and Linux users because it helps automate tasks and boost productivity. By learning both basic and advanced scripting, you can manage systems efficiently, handle files, and perform complex tasks easily. Knowing common interview questions can also aid in job preparation. With regular practice, anyone can become skilled in shell scripting and improve their workflow.

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