Tasks

Don't forget to add a shebang to your scripts and make them executable!

Task: Essential tools

Write a Bash script that installs the following essential Linux packages for you:

  • cmatrix
  • cowsay
  • lolcat
  • cbonsai

After the installation is done, the script should let cowsay inform the user that the installation was successful.

Test your script!

Fun: Run the command cbonsai -i -l -t 0.01 -w 1 🌳

Task: Current directory

Write a Bash script that calculates the total number of files and directories (together) in the current directory. For example, if the current directory has two directories and one file, then the number would be 3. Store the result into a variable.

The output should be the full path to the current working directory with a message telling about the calculated number. Example:

$ whereami.sh
You are in the directory /home/student/scripts
There are 3 files and directories in this directory.

Hints

  • ls -1 shows every file or directory in the current directory on a separate line.

Task: Backup then update

Write a Bash script that does the following:

  1. Create the directory ~/installed_packages if it does not exist. If it exists, it should not through any errors.
  2. Stores the output of the command dnf list --installed into the file ~/installed_packages/dnf.txt.
  3. Stores the output of the command cargo install --list into the file ~/installed_packages/cargo.txt.
  4. Installs system upgrades using dnf.
  5. Installs Cargo updates.
  6. Check if cowsay is installed. Only if not, install it first. After that, cowsay should inform you that installed packages where logged into the directory ~/installed_packages and updates were successfully installed.

If any of the steps above fails, the script should stop and not continue. This can be achieved by adding the following line to the beginning of the script (after the shebang): set -e.

Task: Scripted "Gimme that PDF" 😈

On day 2, you downloaded a PDF given some web page link. We want to write a script now that is generic over the web page link.

It should ask the user for a web page link and then download the PDF if a PDF link was found on that web page.

The script should exit with the status code 1 while printing an error message to stderr in case no PDF link was found on the web page ❌

Otherwise, it should print a message to stdout that the download was successful ✔️

Task: Job scheduler

Warning ⚠️ : This task is not an easy one. Don't give up quickly and ask for help if you don't get further!

In this task, we want to write our own job scheduler.

Understanding how job schedulers work is important when you are working on a computer cluster.

Computer clusters are shared by many users. Therefore, running jobs on a cluster has to be scheduled to make sure that the resources are shared probably.

In this task, we will keep it simple. No aspects of multiple users or any optimizations.

We want to be able to submit a job as a single script (without any dependencies). The submitted scripts should run one after the another.

We will use the program inotifywait. This program can monitor a directory and notify on changes within this directory.

  1. Start Zellij if you are not already using it.
  2. Find out which package provides the program inotifywait and install it.
  3. Read the manual of inotifywait for a better understanding of what it does.
  4. Find out what events mean in the context of inotifywait.
  5. Find out how to tell inotifywait to keep monitoring a directory and not exit after the first event.
  6. Create a new directory called jobs to be monitored.
  7. Create a new directory called logs that will be used later.
  8. Run inotifywait while telling it to monitor the directory jobs. Leave the command running in one Zellij pane and open a second pane to continue the work in.
  9. Create a file outside of the directory jobs and then copy it to the directory jobs.
  10. Look at the output of inotifywait in the first pane after copying the file in to the jobs directory.
  11. Based on that output, choose an event that you want to listen to with inotifywait that tells you when a file is completely written to the directory jobs. Use the manual to read more about specific events.
  12. Find an option that lets you tell inotifywait to only notify when the chosen event occurs.
  13. Find an option that lets you format the output of the notification of inotifywait. Since we only listen on one event and monitor only one directory, an output that shows only the name of the new file should be enough.
  14. Enter the inotifywait command that you have until now in a script. Now, extend it by using a while loop that continuously listens on the notifications of inotifywait. Use the following snippet after replacing …: 
    inotifywait … | while read NEW_SCRIPT_NAME
do
    …
done
  15. After a notification, the body of the while loop should first print the name of the script that was added (NEW_SCRIPT_NAME). Then, the new script should be run.
  16. Save the standard output and standard error of the script into two separate files in the logs directory. If the name of the script is job.sh for example, then the output should be in the files logs/job.sh.out and logs/job.sh.err.

Hints

  • Take care of file permissions.

Task: Job submitter

In this task, we will write a small script called submitter that lets us submit a job script to the scheduler from the last task.

The submitter should take the path to the job script as a single required argument.

The submitter should then copy the job script to the directory jobs while adding the current time and date as a prefix to the new job script name.

Read the manual of the command date to know how to get the current time and date in the following format: 2022-08-22T20:00:00+00:00.

If the name of the job script is job.sh for example, the job script should be named 2022-08-22T20:00:00+00:00_job.sh in the jobs directory.

Use variables while writing the script to make it more understandable.

Hints

  • To save the output of a command into a variable, you have to use the following syntax after replacing …: 
    DATETIME=$(date …)

Task: Submit a job

Write a small job script that requires at least 10 seconds to run (can be simulated with the command sleep 10). Submit that job script by using the submitter from the last task.

Make sure that the scheduler is running in one Zellij pane before submitting.

Submit your job script multiple times and take a look at the pane where scheduler is running to make sure that the job scripts are running one after the other.

Verify the redirection of the standard output and standard error in the directory logs.