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devexamples

Tail Follow Streaming Log Filter

Stream growing log files with tail -F and grep pipelines, highlighting patterns and stopping cleanly on signals.

BashCli Tooling

Code

snippet
#!/usr/bin/env bash
set -euo pipefail

readonly LOG_FILE="${1:-/var/log/app/application.log}"
readonly PATTERNS='ERROR|WARN|Traceback'

running=true
on_term() { running=false; }
trap on_term INT TERM

stream_logs() {
  # -F 处理轮转：文件被重建后继续跟随
  tail -F --lines=50 "${LOG_FILE}" 2>/dev/null \
    | grep --line-buffered -E "${PATTERNS}" \
    | while IFS= read -r line; do
        case "$line" in
          *ERROR*)     printf '\033[31m%s\033[0m\n' "$line" ;;
          *WARN*)      printf '\033[33m%s\033[0m\n' "$line" ;;
          *Traceback*) printf '\033[35m%s\033[0m\n' "$line" ;;
        esac
      done
}

[[ -f "${LOG_FILE}" ]] || { echo "日志文件不存在: ${LOG_FILE}" >&2; exit 1; }

echo "跟随 ${LOG_FILE} 中的 ${PATTERNS}，Ctrl-C 退出"
stream_logs &

readonly TAIL_PID=$!
while $running; do
  sleep 1
  kill -0 "${TAIL_PID}" 2>/dev/null || running=false
done

kill "${TAIL_PID}" 2>/dev/null || true
wait "${TAIL_PID}" 2>/dev/null || true
echo "日志流已停止"

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