“subprocess.Popen” - 检查成功和错误

Question

我想检查一个子进程是成功完成还是失败了。目前我已经提出了一个解决方案，但我不确定它是否正确和可靠。是否保证每个进程仅将其错误输出到 stderr 尊重stdout:

注意：我对重定向/打印输出不感兴趣。我已经知道该怎么做了。

pipe = subprocess.Popen(command,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE,
                                universal_newlines=True)

if "" == pipe.stdout.readline():
    print("Success")
    self.isCommandExectutionSuccessful = True

if not "" == pipe.stderr.readline():
    print("Error")
    self.isCommandExectutionSuccessful = True

或者：

   if "" == pipe.stdout.readline():
       print("Success")
       self.isCommandExectutionSuccessful = True
   else:
       print("Error")
       self.isCommandExectutionSuccessful = False

和：

   if not "" == pipe.stderr.readline():
       print("Success")
       self.isCommandExectutionSuccessful = True
   else:
       print("Error")
       self.isCommandExectutionSuccessful = False

Answer 1

这就是我最终做到的：

    # Call a system process
    try:
        # universal_newlines - makes manual decoding of subprocess.stdout unnecessary
        output = subprocess.check_output(command,
                                         stderr=subprocess.STDOUT,
                                         universal_newlines=True)

        # Print out command's standard output (elegant)
        self.textEdit_CommandLineOutput.insertPlainText(output)
        self.isCommandExecutionSuccessful = True

    except subprocess.CalledProcessError as error:
        self.isCommandExecutionSuccessful = False

        errorMessage = ">>> Error while executing:\n"\
                       + command\
                       + "\n>>> Returned with error:\n"\
                       + str(error.output)
        self.textEdit_CommandLineOutput.append(errorMessage)

        QMessageBox.critical(None,
                             "ERROR",
                             errorMessage)
        print("Error: " + errorMessage)

    except FileNotFoundError as error:
        errorMessage = error.strerror
        QMessageBox.critical(None,
                             "ERROR",
                             errorMessage)
        print("Error: ", errorMessage)

我希望它对其他人有用。

Answer 2

带有检查返回码、标准输出和标准错误的完整解决方案：

import subprocess as sp

# ok
pipe = sp.Popen( 'ls /bin', shell=True, stdout=sp.PIPE, stderr=sp.PIPE )
# res = tuple (stdout, stderr)
res = pipe.communicate()
print("retcode =", pipe.returncode)
print("res =", res)
print("stderr =", res[1])
for line in res[0].decode(encoding='utf-8').split('\n'):
  print(line)

# with error
pipe = sp.Popen( 'ls /bing', shell=True, stdout=sp.PIPE, stderr=sp.PIPE )
res = pipe.communicate()
print("retcode =", pipe.returncode)
print("res =", res)
print("stderr =", res[1])

打印：

retcode = 0
res = (b'bash\nbunzip2\nbusybox\nbzcat\n...zmore\nznew\n', b'')
stderr = b''
bash
bunzip2
busybox
bzcat
...
zmore
znew

retcode = 2
res = (b'', b"ls: cannot access '/bing': No such file or directory\n")
stderr = b"ls: cannot access '/bing': No such file or directory\n"

Answer 3

你需要对流程的输出做些什么吗？

check_call 方法在这里可能很有用。在此处查看 python 文档：https://docs.python.org/2/library/subprocess.html#subprocess.check_call

然后您可以按如下方式使用它：

try:
  subprocess.check_call(command)
except subprocess.CalledProcessError:
  # There was an error - command exited with non-zero code

但是，这依赖于 command 返回退出代码 0 表示成功完成，返回非零值表示错误。

如果您还需要捕获输出，那么check_output 方法可能更合适。如果您也需要，仍然可以重定向标准错误。

try:
  proc = subprocess.check_output(command, stderr=subprocess.STDOUT)
  # do something with output
except subprocess.CalledProcessError:
  # There was an error - command exited with non-zero code

在此处查看文档：https://docs.python.org/2/library/subprocess.html#subprocess.check_output

Answer 4

您可以使用 check_call() 方法检查进程的返回码。 如果进程返回非零值，则会引发 CalledProcessError。

Answer 5

      output,error=pipe.communicate()

这将等待命令完成并根据命令的状态为您提供输出或错误。