tail: don't panic on '-c +N' with a huge N - #14034
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`tail -c +N FILE` on a regular file larger than the block size seeks to byte N-1. When N-1 exceeds what the OS can seek to (any offset above i64::MAX always fails with EINVAL), the `.unwrap()` aborted the process. Clamp the start offset to the file length. A start beyond the end of the file produces no output (matching GNU `tail`), and clamping also avoids seeking to an offset the OS cannot represent — so the pathological case yields empty output instead of panicking. Behavior is unchanged for valid offsets. Adds a regression test (verified failing before the fix). Closes uutils#13887.
sylvestre
reviewed
Aug 19, 2026
| // at 0. It seems to treat `+0` and `+1` as the same thing. | ||
| file.seek(SeekFrom::Start(*count - 1)).unwrap(); | ||
| // | ||
| // Clamp the start offset to the file length. A start beyond the end of the file |
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I don't think we need 4 lines comme r for this
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tail -c +N FILEon a regular file larger than the block size seeks to byte N-1. When N-1 exceeds what the OS can seek to (any offset above i64::MAX always fails with EINVAL), the.unwrap()aborted the process.Clamp the start offset to the file length. A start beyond the end of the file produces no output (matching GNU
tail), and clamping also avoids seeking to an offset the OS cannot represent — so the pathological case yields empty output instead of panicking. Behavior is unchanged for valid offsets.Adds a regression test (verified failing before the fix). Closes #13887.
Closes #13887.
tail -c +N FILE on a regular file larger than the block size seeks to byte N-1. When N-1 exceeds what the OS can seek to (any offset above i64::MAX fails with EINVAL), the .unwrap() aborted the process:
Fix: clamp the start offset to the file length. A start beyond EOF produces no output (matching GNU tail), and clamping avoids the un-seekable offset
entirely. Behavior is unchanged for valid offsets.
Adds a regression test (verified failing before the fix). cargo fmt, cargo clippy, and the tail test suite pass.