Print only the log lines whose level is ERROR.
Each log line looks like `<timestamp> <LEVEL> <message>`.
Print only the lines whose level token (the second whitespace-separated word) is exactly `ERROR`.
Test input:
2024-01-01 INFO start
2024-01-01 ERROR disk full
2024-01-01 WARN slow
2024-01-01 ERROR oom
Expected output:
2024-01-01 ERROR disk full
2024-01-01 ERROR oom
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