Level 20: Your First Script

A service is asking for a password and a 4-digit PIN. There are 10,000 possible PINs (0000 to 9999).

If you try to type these by hand, you're not an operator; you're a typewriter. This is the perfect moment to stop manual work and start automating.

The goal is to create a loop that tries every single PIN until the service stops telling us "Wrong." I used seq -w to generate the numbers (the -w is key because it keeps the leading zeros, so 1 becomes 0001) and piped them into nc.

for pin in $(seq -w 0000 9999); do
    echo "REDACTED $pin" | nc -w 1 localhost 30002 | grep -v Wrong && break
done

The grep -v Wrong part tells the loop: "Keep going as long as the response contains the word 'Wrong'. The moment it doesn't, stop."

The loop breaks, and the correct password is revealed.

Result: REDACTED

TL;DR: When the possibilities are finite but too many for a human, write a Bash loop with seq and nc to brute-force the answer.