| name | long-task-watcher |
| visibility | public |
| triggers | monitor, tail, progress, background, long task, watch, 진행 상황, 백그라운드, 모니터링 |
| description | Reliable progress watching for long-running background commands (training runs, live audits, batch jobs, CI) without losing output to stdout buffering. Prefer post-completion cat-and-grep over tail -F. |
Long-Task Watcher
Patterns for tracking a long-running background command and surfacing its
events without the classic tail -F | grep buffering trap: matching lines can
sit in a 4KB stdout block buffer and never emit within the watch window, so a
watcher waits forever on output that is already on disk.
Pattern selection
| Situation | Pattern | Why |
|---|
| Task finishes within minutes | Wait for completion, then cat <logfile> | grep -E "<filter>" | No inotify/buffering dependency; no lost lines. Default choice. |
| Long task, frequent progress lines | stdbuf -oL tail -F <logfile> | stdbuf -oL grep --line-buffered "<filter>" | Forces line-buffering at every pipe stage (macOS: needs coreutils). |
| External state (CI, deploy, queue) | Polling loop: while true; do <one-shot status call>; sleep 30; done | The external status API is the truth; tailing local output adds nothing. |
| Task should stop the watch when it dies | Add kill -0 $PID 2>/dev/null || break to the polling loop | Breaks immediately on process exit instead of waiting for a timeout. |
Rules
- Redirect long-run stdout/stderr to a file from the start (
... > run.log 2>&1); never rely on scrollback.
- After the task exits, one
cat-and-grep pass over the log is more reliable than any live tail.
- Watch loops need a hard timeout; a watcher without one outlives dead tasks.
- Archive logs to a stable location (
.audit/ convention) before summarizing, so the evidence survives the session.
