OverTheWire Bandit: Level 7 → 8 Walkthrough

In the previous level we had to find a file lost somewhere on the whole server. Now we know exactly which file holds the password, but the problem is a different one: that file is huge, and what we want is a single line among thousands. Time to meet two essential tools for working with text in Linux: grep to filter lines and awk to keep just the part of the line we care about.

Passwords are shown as [REDACTED], following the OverTheWire rules.

Connecting to level 7

$ sshpass -p '[REDACTED]' ssh bandit7@bandit.labs.overthewire.org -p 2220
bandit7@bandit:~$ export TERM=xterm

The challenge

According to the level 8 page, the password is stored in the file data.txt, next to the word millionth.

bandit7@bandit:~$ ls
data.txt

If we try opening it straight away with cat data.txt, the terminal fills up with line after line: each one has a word followed by a string that looks like a password. Reading it by eye isn’t an option. We need to filter.

To get an idea of a file’s size before opening it, wc -l data.txt tells you how many lines it has. That way you don’t flood your terminal.

Filtering with grep

bandit7@bandit:~$ cat data.txt | grep "millionth"
millionth	[REDACTED]

Two pieces are at work here:

• The pipe | connects the standard output (stdout) of the command on the left to the standard input (stdin) of the one on the right. cat dumps the whole file, but instead of going to the screen, that text flows into grep.
• grep "millionth" reads line by line and only lets through the lines that contain the pattern millionth. Everything else is dropped.

The result: out of the whole file, only the line we want survives, with the word and the password.

Keeping only the password with awk

The previous line already gives us the password, but the word millionth is still in front of it. To get only the password, we add one more link to the chain:

bandit7@bandit:~$ cat data.txt | grep "millionth" | awk '{print $2}'
[REDACTED]

awk is a tool (actually a small programming language) for processing text by columns:

• By default, it splits each line into fields using whitespace (spaces and tabs) as the separator.
• $1 is the first field (the word millionth), $2 is the second (the password), and $0 would be the whole line.
• {print $2} means “for every line you receive, print the second field”.

Notice that the awk program goes inside single quotes. This matters: with double quotes, the shell would try to replace $2 with one of its own variables (which would be empty) before awk ever saw it, and the command wouldn’t do what you expect.

Other ways to do it

1. Without cat: grep can read the file directly

bandit7@bandit:~$ grep "millionth" data.txt
millionth	[REDACTED]

grep accepts the file name as an argument, so cat data.txt | isn’t needed. It works the same, but saves you a process. It even has a name: useless use of cat. Using cat isn’t wrong, just redundant.

2. With awk alone

bandit7@bandit:~$ awk '/millionth/ {print $2}' data.txt
[REDACTED]

awk can filter too: the pattern between slashes, /millionth/, does grep’s job, and the {print $2} block only runs on matching lines. A single command does the work of all three.

3. With cut and whole-word matching

bandit7@bandit:~$ grep -w "millionth" data.txt | cut -f2
[REDACTED]

• grep -w matches the whole word: it wouldn’t match something like millionths if it existed in the file. It doesn’t change the result here, but it’s a good habit when you’re looking for a specific word.
• cut -f2 extracts the second field, but only if the separator is a tab, which is cut’s default (unlike awk, which accepts any whitespace). You can check which separator is used with grep millionth data.txt | cat -A: tabs show up as ^I.

Moving on to the next level

bandit7@bandit:~$ exit
$ sshpass -p '[REDACTED]' ssh bandit8@bandit.labs.overthewire.org -p 2220

Summary

Command / concept	What it’s for
Pipe (vertical bar)	Pass one command’s output as the next command’s input
grep pattern file	Show only the lines containing the pattern
grep -w	Match the whole word
awk '{print $2}'	Print the second field of each line
awk '/pattern/ {print $2}'	Filter and print a field in one step
cut -f2	Extract the second tab-separated field
wc -l	Count the lines in a file
Single quotes	Stop the shell from interpreting $2 before awk does