你如何處理Python中的管道和輸出？

Question

我試圖在我的python腳本中執行此命令：

avprobeCommand = "avprobe -of json -show_streams {0} | grep '\"duration\"' | sed -n 1p | sed 's/ //g'".format(hiOutput)
output = subprocess.check_output([avprobeCommand])

而且我一直在：

    Traceback (most recent call last):
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 505, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/Users/jmakaila/Documents/Development/Present/Web/video_dev/present-live-transcoder/Transcoder.py", line 60, in transcode
    output = subprocess.check_output([avprobeCommand])
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 537, in check_output
    process = Popen(stdout=PIPE, *popenargs, **kwargs)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 679, in __init__
    errread, errwrite)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1228, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

我已經嘗試將args拆分了，但是我仍然為-of json -show_streams部分收到錯誤，對於記錄，它看起來像這樣：

subprocess.check_output(["avprobe", "-of json", "-show_streams", "{0}".format(hiOutput)

Answer 1

將命令作為字符串傳遞，並傳遞shell=True ：

import pipes
import subprocess

avprobeCommand = """avprobe -of json -show_streams {0} | grep '"duration"' | sed -n 1p | sed 's/ //g'""".format(pipes.quote(hiOutput))
output = subprocess.check_output(avprobeCommand, shell=True)

UPDATE ：參數應該使用pipes.quote進行轉義。 （使用shlex.quote如果你使用Python 3.3+）。

Answer 2

在您的情況下，您可以將后處理移動到Python：

import json
from subprocess import check_output as qx

data = json.loads(qx(["avprobe", "-of", "json", "-show_streams", hiOutput]))
result = data["duration"]         # grep '"duration"'
             .partition("\n")[0]  # sed -n 1p
             .replace(" ", "")    # sed 's/ //g'

有關更一般的情況，請參閱如何使用subprocess.Popen通過管道連接多個進程？