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Interview question · Application & API Security

Practical coding: walk a directory tree and find files containing a pattern, safely.

An easy coding warm-up with traps a security engineer should spot: symlinks, huge files, unreadable files and paths outside the tree. The scored answer handles each and tests it.

easyNewPreparation tags: Google, Microsoft, AmazonUpdated Nov 2026

An easy coding warm-up with traps a security engineer should spot: symlinks, huge files, unreadable files and paths outside the tree. The scored answer handles each and tests it.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

You need to write a script that finds configuration files containing secrets across a large directory tree, and an agent will reuse it on repositories.

  1. Why should the walk not follow symlinks?
  2. What else should be skipped?
  3. How do you protect against huge files?
  4. How should errors be handled?
  5. How would you test it?
  6. What would the script look like?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
Next in this trackPractical coding: build a web crawler, start simple, then make it concurrent and safe.Next in this trackWalk through the security attributes of a session cookie: Secure, HttpOnly, SameSite, Domain, Path and the __Host- prefix.Next in this trackDesign the session lifecycle for a web app: creation, rotation, timeouts, logout and revocation after a password change.
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