Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Amazon SWE interview with a scripting problem that looked straightforward on the surface but had a lot of edge cases to juggle. The kind of question where you think you're done and then they keep pulling threads.

Questions Asked (1)

Write a POSIX-compliant shell script that takes a username and a file path as arguments and outputs a single line formatted as '<timestamp> <license> <user@hostname>'. The script should validate both arguments, compute an ISO 8601 UTC timestamp, derive a license string from the file contents, handle file errors and non-ASCII paths, return meaningful exit codes, and include a basic test outline.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

I started with the argument parsing and exit codes because that felt concrete, but I got tripped up on the license extraction part.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases, then outline a POSIX-compliant script structure with argument validation, timestamp generation, license derivation, and error handling. Walk through the script logic step-by-step, emphasizing portability, exit codes, and testability, and finish with a brief test outline.

Pro tip: Use `set -e` and `set -u` for robustness, but be aware that POSIX sh doesn't support `pipefail`; handle errors explicitly. Also, for non-ASCII paths, ensure you quote variables and use `LC_ALL=C` for consistent byte-wise operations.

1. Clarify requirements and constraints

Ask clarifying questions about the expected license derivation (e.g., hash of file contents), timestamp format, and error handling expectations. Confirm POSIX compliance and testability.

2. Design script structure

Outline the script: shebang, argument count check, validation of username and file path, timestamp generation, license computation, and output formatting. Plan exit codes for different failure modes.

3. Implement core logic

Write POSIX-compliant code: use `date -u +%Y-%m-%dT%H:%M:%SZ` for ISO 8601 UTC, compute license via `cksum` or `md5sum` (if available) on file contents, and construct the output line with `printf`.

4. Handle errors and edge cases

Validate arguments: non-empty username, file exists and is readable. Handle non-ASCII paths by quoting variables and avoiding locale-dependent operations. Return meaningful exit codes (e.g., 1 for usage, 2 for file error).

5. Outline tests

Describe a basic test outline: test with valid inputs, missing arguments, non-existent file, unreadable file, and non-ASCII path. Verify output format and exit codes.

Key Points to Mention

POSIX compliance: avoid bashisms, use `#!/bin/sh`, and rely on POSIX utilities like `date`, `printf`, and `cksum`.
Argument validation: check `$#` equals 2, ensure username is non-empty, and file path exists and is readable.
Timestamp: use `date -u +%Y-%m-%dT%H:%M:%SZ` for ISO 8601 UTC.
License derivation: use `cksum` (POSIX) or `md5sum` (if available) on file contents; consider fallback if neither is available.
Error handling: use `set -e` and `set -u`, but handle errors explicitly; return distinct exit codes (e.g., 1 for usage, 2 for file error).
Non-ASCII paths: quote all variables, use `LC_ALL=C` for consistent byte-wise operations, and avoid locale-dependent commands.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.