python pipe stdout 实现cat|grep 功能

从hdfs里获取希望的数据：

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import subprocess     for day in range(22, 23):     for h in range(17, 24):         filename = "metadata-2018-10-%02d-%02d.txt" % (day, h)         cmd = "hdfs dfs -text /flume/metadata/2018/10/%02d/%02d/*.snappy" % (day, h)         print(cmd)         #cmd = "cat *.py"         cmd = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)         f = open(filename, "w")         for line in cmd.stdout:             try:               arr = line.split("^")               if len(line) > 100 and arr[6] == "6":                 #print(line)                 f.write(" ".join(arr[:32]) + " " + arr[95] + "\n")             except Exception as e:                 print(e, "fuck error", line)         f.close()         #import sys         #sys.exit(0)