README.md

FE04

100pt

Briefing

Download the file and filter down to the username according to criteria below.

The username you are looking for has x as the 3rd character, followed immediately by a number from 2 to 6, it has a Z character in it and the last character is S.

When you have the username, submit it as the flag.

Solution

The provided file can be found here.

Grep on steriods, let's break it down step by step.

We have the criteria of:

• has x as the 3rd character
• a number from 2-6 immediately after
• contains the character Z
• finishes off with S

Solution 1:

You can do this in many ways, but the easiest would likely be grep + regex to filter:

grep -P '^..x[2-6].*Z.*S$' 50k-users.txt

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Solution 2:

So, there's this cool command called grep, where you can search for certain expressions. I grepped the inital file for anything that met one of the first 3 requirements, and then piped it out to another file, to rinse and repeat. After satisfying the first 3 requirements, I manually removed everything left that didn't finish with S, leaving me with 6 strings. Finally, I had a read through the 6 to see what one was right, and submitted it as the flag, commands used below:

grep -ex2 -ex3 -ex4 -ex5 50k-users.txt > step1.txt
grep 'Z' step1.txt > step2.txt
grep "S" step2.txt > final.txt

Flag

Flag: YXx52hsi3ZQ5b9rS