long-task-watcher

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.