텍스트 처리 (grep·sed·awk)

grep -n ERROR app.log                       # 줄 번호와 함께
grep -c ERROR app.log                       # 2
grep -A2 'ERROR.*500' app.log               # 스택 트레이스 2줄 포함
grep -E ' (5[0-9]{2}) ' app.log             # 5xx 응답 줄
grep -oE '/api/[a-z]+' app.log | sort | uniq -c

4:2026-09-10 09:00:07 ERROR [http-3] POST /api/orders 500 45ms
8:2026-09-10 09:01:10 ERROR [http-5] GET /api/pay 502 3001ms
2
      3 /api/orders
      1 /api/pay

grep -vE '^\s*(#|$)' app.properties         # 주석·빈 줄 제외
sed -i.bak 's/^server.port=.*/server.port=9090/' app.properties
sed -i 's/^logging.level.root=DEBUG/logging.level.root=INFO/' app.properties
sed -i '/password/s/=.*/=****/' app.properties
diff app.properties.bak app.properties

1c1
< server.port=8080
---
> server.port=9090
5c5
< logging.level.root=DEBUG
---
> logging.level.root=INFO

awk '/^2026/{print $3}' app.log | sort | uniq -c
grep -E '[0-9]+ms
  

 app.log | awk '{ms=$NF+0; n++; s+=ms; if(ms>mx)mx=ms}
  END{printf "count=%d sum=%d avg=%.1f max=%d\n", n, s, s/n, mx}'
awk '/ms$/ && $6 ~ /^\// {ms=$NF+0; c[$6]++; t[$6]+=ms}
  END{for(k in c) printf "%-16s n=%d avg=%.0fms\n", k, c[k], t[k]/c[k]}' app.log | sort

      2 ERROR
      4 INFO
      1 WARN
count=5 sum=3067 avg=613.4 max=3001
/api/orders      n=2 avg=28ms
/api/orders/7    n=1 avg=8ms
/api/pay         n=1 avg=3001ms
/health          n=1 avg=1ms

cd /var/log/myapp
grep -c ERROR app.log                       # 1. 규모 파악
grep ERROR app.log | cut -c12-16 | uniq -c  # 2. 분 단위 분포
sed -n '/14:32:00/,/14:35:00/p' app.log > incident.log   # 3. 구간 저장
grep -E '^(java|org)\.' incident.log | sort | uniq -c | sort -rn   # 4. 예외 종류
grep -B3 'Read timed out' incident.log | head -n 20   # 5. 직전 요청 확인