Bandit Level 8: The Unique Line Challenge (Meeting `sort` and `uniq`)

(The short answer for this challenge is available at the end of this post.)

Introduction: When Repetition is a Problem

You’ve learned to grep for a specific word, which is incredibly useful. But what if the password isn’t just next to a word, but is defined by its uniqueness? Welcome to Bandit Level 8, where you’ll encounter a file filled with many lines, but only one of them holds the secret to the next level because it appears only once.

The level description for Bandit Level 8 tells us:

The password for the next level is stored in the file data.txt and is the only line that occurs once.

This is a classic text processing puzzle! We need a way to filter out all the duplicate lines and show only the truly unique ones. For this, we’ll introduce two new essential Linux commands: sort and uniq, and we’ll chain them together using the mighty pipe (|).

Level 8: The Harmony of sort and uniq (Thanks to the Pipe)

You’ve just logged in as bandit8 with the password from Level 7. Let’s ls to confirm our file:

ls

You’ll see:

data.txt

Excellent. Now, if you cat data.txt, you’ll probably see a very long list of lines, many of which are identical. Trying to manually find the unique one would be like finding a specific grain of sand on a beach with a magnifying glass.

Command 1: sort (The Organizer)

The sort command, as its name implies, sorts lines of text alphabetically or numerically. Why do we need this? Because uniq works best on sorted input. Imagine you have a stack of identical papers mixed with one unique paper. If they’re all shuffled, it’s hard to find the unique one. If you sort them into piles of identical papers, the unique one will be in its own pile.

To sort data.txt, you’d use:

sort data.txt

This will output all the lines from data.txt, but now they’re in alphabetical order. Still a lot of lines, but now the duplicates are grouped together.

Command 2: uniq (The Duplicates Destroyer)

The uniq command filters out (or counts) adjacent duplicate lines. This is why sort is crucial first! Without sorting, uniq would only catch duplicates that happen to be right next to each other.

The basic uniq command, when run on sorted input, will show each unique line, effectively removing consecutive duplicates. But we want lines that occur only once. For that, uniq has a special option: -u.

• uniq: Removes consecutive duplicate lines.
• uniq -u: Only prints unique lines (those that appear exactly once).

The Pipe (|): Chaining Commands

Here’s where the magic happens. The pipe symbol (|) takes the output of the command on its left and feeds it as the input to the command on its right. It’s like a conveyor belt for data!

So, to solve this level, we’ll:

1. sort the data.txt file.
2. Pipe (|) the sorted output to uniq -u.

The full command looks like this:

sort data.txt | uniq -u

Type this into your terminal and press Enter. sort will process the file, send its output to uniq -u, and uniq -u will then print only the line that appeared exactly once.

That single line printed to your screen is the password for bandit9! Copy it carefully.

Moving Onward:

Got that password? You’re a text-processing wizard!

exit

And finally, connect to the next challenge:

ssh [email protected] -p 2220

Enter your hard-won password, and you’re logged into bandit9. You’ve truly mastered the art of extracting unique information!

Conclusion: The Power of Chained Commands

You’ve successfully conquered Bandit Level 8, adding powerful text processing tools to your Linux command-line arsenal:

• The sort command for organizing textual data.
• The uniq command (especially with -u) for finding unique lines.
• The incredibly versatile pipe (|) for chaining commands together, creating powerful data workflows.

Understanding how to combine commands with pipes is a fundamental skill in Linux, enabling you to perform complex operations with simple, concise commands.

SPOILER ALERT: Short Answer for Bandit Level 8

1. Log in as bandit8.
2. Combine sort and uniq -u using a pipe:
   sort data.txt | uniq -u

3. The single line of output is the password for bandit9.
4. Copy the password.

Continue to Bandit Level 9!