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Bandit8->9

Level Goal

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

Commands useful to solve the level

Helpful Reading Material

Where to start?

To get more information about the file analysis, go to the previous challenge.

We now need to get the only line of text that occurs only once in the file data.txt. To do so we'll do the process in reverse.

Part 1 : Uniquifying the file

The uniq utility allows us to discard repeated input lines, what it does is that it compares the consecutive lines to see if they're (or aren't) identical to each other.

Hint

Using the uniq gnu documentation, can you figure out what option we need to keep only the input lines that occurs only once?

Solution

The option -u is the option we'll need to complete our goal. Let's break down what it does. Here is a quote from the documentation :

The -u option : "Discard the last line that would be output for a repeated input group. When used by itself, this option causes uniq to print unique lines, and nothing else."
First let's try and see what would be the last line outputed for a repeated input group : it is the first line of the group. This means that uniq -u discards the only line which would be outputed for a group. This indeed means that uniq -u only prints the unique lines.

However we know from the same documentation that uniq operates on consecutive lines, thus we need a way to make the lines consecutive to compare them.

Part 2 : Sorting text files

We need a way to sort the input to apply our uniq filter to it.

Hint

By looking into the sort gnu documentation, can you figure out how to sort the input for the uniq filter to work?

Solution

It's fairly simple, we don't need any option at all. By running sort data.txt, we will output the result of the sorted output to stdout.

Full Solution

sort data.txt | uniq -u is the full command that will allow us to get the full password string.

  1. sort data.txt will allow us to sort the input in order for uniq to see the consecutive repeated lines.
  2. | the pipe will allow the sort and uniq processes to communicate.
  3. uniq -u will dump the only unique line to stdout.

You can now jump to the next level