分析从某android手机上取得app的日志log.txt，若日志出现“error，warning，crash”其中任一个单词，则将该行日志输出，正确的语句是：
cat log.txt|grep -E "error" -E "warning" -E "crash"
grep -E "error|warning|crash" log.txt
grep "error" log.txt|grep "warning" log.txt|grep "crash" log.txt
grep "error|warning|crash" log.txt
