60 lines
1.5 KiB
Bash
60 lines
1.5 KiB
Bash
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#!/usr/bin/env bash
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# Keep a log file capped by trimming from the front.
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# Usage:
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# ./log-trim-daemon.sh --file /path/to/app.log --max-mb 5 --interval-sec 3
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set -euo pipefail
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FILE=""
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MAX_MB=5
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INTERVAL_SEC=3
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while [ $# -gt 0 ]; do
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case "$1" in
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--file) FILE="${2:-}"; shift 2 ;;
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--max-mb) MAX_MB="${2:-}"; shift 2 ;;
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--interval-sec) INTERVAL_SEC="${2:-}"; shift 2 ;;
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-h|--help)
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echo "Usage: $0 --file PATH [--max-mb 5] [--interval-sec 3]"
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exit 0
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;;
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*)
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echo "Unknown arg: $1" >&2
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exit 2
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;;
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esac
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done
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if [ -z "${FILE}" ]; then
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echo "Missing --file" >&2
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exit 2
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fi
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MAX_BYTES=$((MAX_MB * 1024 * 1024))
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TMP="${FILE}.trimtmp.$$"
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LOCK="${FILE}.trimlock"
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mkdir -p "$(dirname "$FILE")"
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touch "$FILE" 2>/dev/null || true
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while true; do
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if [ -f "$FILE" ]; then
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size=$(stat -c%s "$FILE" 2>/dev/null || echo 0)
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if [ "${size:-0}" -gt "$MAX_BYTES" ]; then
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# Keep only the last MAX_BYTES bytes.
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# IMPORTANT: do NOT replace the file inode (mv)，否则 tail -f/编辑器可能还在看旧 inode，
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# 会出现“日志不更新/看不到最新内容”的错觉。这里用 copy+truncate 保持 inode 不变。
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(
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flock -w 2 9 || exit 0
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tail -c "$MAX_BYTES" "$FILE" > "$TMP" 2>/dev/null || true
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# 覆盖写回同一文件（inode 不变）
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if [ -s "$TMP" ]; then
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cat "$TMP" > "$FILE" 2>/dev/null || true
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fi
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rm -f "$TMP" 2>/dev/null || true
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) 9>"$LOCK" || true
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fi
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fi
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sleep "$INTERVAL_SEC"
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done
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