Day 5 : Advanced Linux Shell Scripting for DevOps Engineers with User Management

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Task 1 : Create Directories Using Shell Script :

- Write a bash script createDirectories.sh that, when executed with three arguments (directory name, start number of directories, and end number of directories), creates a specified number of directories with a dynamic directory name.

- Example 1: When executed as ./createDirectories.sh day 1 90, it creates 90 directories as day1 day2 day3 ... day90.

- Example 2: When executed as ./createDirectories.sh Movie 20 50, it creates 31 directories as Movie20 Movie21 Movie22 ... Movie50.

Solution :

We will create a createdirectories.sh file using vim and write a script that accepts 3 values from the user:

• $1: Directory_name

• $2: Starting no.

• $3: End no.

We will use a for loop to create directories as specified by the user.

After this, we will save the file by pressing Esc and typing :wq.
We will give it execute permission using chmod +x createdirectories. Finally, we will run the script with ./createdirectories day 1 90. This will create 90 directories day1, day2, …..day90.

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Task 2 : Create a Script to Backup All Your Work :

Solution :

Our files are stored in the data folder. We will take a backup of the files from the data folder to the backup_folder. First, we will create the backup_folder using mkdir and then write a script to take the backup.

After that, we will give execution permission to the file using chmod +x backup.sh Then, we will execute it with ./backup.sh

Now we can see that our backup is complete, and all the files are stored in the backup_folder.

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Task 3 : Read About Cron and Crontab to Automate the Backup Script :

Solution :

What is Cron ? Cron is a tool that helps you schedule tasks to run automatically at specific times. It runs in the background to take care of these tasks for you.

What is Crontab ? Crontab is a file where you write down the tasks you want to schedule and when you want them to run. It’s like a planner for your automated jobs.

Crontab Syntax Overview :

[Minute]   [Hour]   [DayOfMonth]   [Month]   [DayOfWeek]   [Command]

Examples :

If we want the task done every minute then we write

 *  *  *  *  *  [command]

If we want the task done every day at 4am (4)

 0  4  *  *  *  [command]

If we want the task done every sunday at 4pm (16)

 0  16  *  *  0 [command]

Lets make a demo crontab which will print every minute “Hello !” in text file

This is the interface you will see in crontab -e

To print every minute , we use * * * * * echo “Hello !” » [destination]

Explaination :

• crontab -l: This command shows the list of current crontab entries.

• crontab -e: This command is used to create or edit a crontab file.

  After executing this command, it will ask you to choose which editor you want to work with (e.g., nano, vim, etc.).

  Checking the Output:

  • After setting up a cron job, you can check the output by using ls to see if the file is created.

  • If the job is scheduled to run every minute, the file may not be displayed immediately due to the timing of the next execution.

  • After a minute, you can check again, and you should see the demo.txt file, which will contain "Hello!" printed every minute.

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Task 4 : Read About User Management :

A user is an entity in a Linux operating system that can manipulate files and perform several other operations. Each user is assigned an ID that is unique within the system. IDs 0 to 999 are assigned to system users, and local user IDs start from 1000 onwards.

Create 2 users and display their usernames :

Solution :

To create user we write command sudo useradd user_name . I created 2 users

You can display the usernames of the created users by checking the /etc/passwd file or using the getent command:

Here we completed our todays task !

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