Linux Output Multiplexing

Introduction

In a highly digitalized world where Superheroes use technology to fight crime, there lies the magnificent "Guardians of the Command Line" team. They are tasked with battling against digital crimes and their arch-enemy, the infamous "Syntax Overlord". The Overlord has developed a nefarious code that clogs the system logs of the Superhero mainframe, aiming to disorient the heroes by causing a chaotic surge of information.

To counter this attack, the team needs to design a smart logging system that can simultaneously display key information on screen for real-time monitoring, and archive it for future analysis. This is where the power of the tee command comes into play. It's up to our heroes to harness this skill to effectively monitor and route critical output, ensuring their systems remain uncompromised in the face of the Syntax Overlord's schemes. Are you ready to join them and secure the integrity of their systems?

Skills Graph

Become Familiar with tee

In this step, you will learn how to use the tee command to both view and store output simultaneously. First, let's create a test file to work with. Navigate to the default working path /home/labex/project.

Create a simple "Hello, World!" script:

echo "Hello, World." > hello.txt

Now, use tee to display the contents of "hello.txt" while also copying it to another file:

cat hello.txt | tee copy.txt

You should see the output "Hello, World!" displayed on your screen and the same content duplicated into the file copy.txt in your current directory.

Redirecting Standard Error with tee

The Superheroes need the ability to catch any errors in their system logs. This step involves tee and its capability to capture standard error.

Let's create a script that outputs both standard output and standard error:

echo "This is standard output"
ls /nonexistentfile 2> error.log

Now amend the script to redirect the error into both the terminal and the error.log file:

{
  echo "This is standard output"
  ls /nonexistentfile
} 2>&1 | tee error.log

Run the script and observe that the standard error is indeed displayed on the terminal and logged into error.log.

2>&1: Redirects the standard error output to the standard output, so that both the standard output and the standard error output are piped to the next command.

Appending Output with tee

To ensure that logs are kept intact, it is important to know how to append outputs instead of overwriting them. In this step, continue to use tee to append data.

First, run a command that outputs system information, with appended logs:

uname -a | tee -a system_info.log

Repeat the previous command a couple of times to see the content being appended in system_info.log.

The -a option in tee -a system_info.log means to append to the file rather than overwrite it.

Summary

In this lab, you've stepped into the shoes of the "Guardians of the Command Line", learning to wield the power of tee to combat against digital mayhem caused by the Syntax Overlord. You've mastered the basics of outputting and saving data simultaneously, redirecting standard error for error logging, and appending data logs instead of overwriting them. The practical hands-on approach should cement the tee command's capabilities in a context mimicking real-world superhero tasks. This lab's design aimed to combine fun with learning, paving the way for beginners to confidently manage output in Linux. Your gain from this experience is not just in understanding the tee command but also in realizing the importance of effective data logging, which is crucial for system administration and troubleshooting.