在 subprocess.check_output 中将 stderr 重定向到 stdout 不会打印出错误消息。 为什么？

Question

I am calling a shell command from python's subprocess module, using check_output.

As shown below, I try to get the error message of executing a wrong shell command lsl -l , by redirecting stderr to stdout. But it does not work apparently. Why?

In [5]: subprocess.check_output("lsl -l", shell=True,stderr=subprocess.STDOUT)                                             
---------------------------------------------------------------------------
CalledProcessError                        Traceback (most recent call last)
<ipython-input-5-8dd15c76eb0f> in <module>
----> 1 subprocess.check_output("lsl -l", shell=True,stderr=subprocess.STDOUT)

/usr/lib/python3.5/subprocess.py in check_output(timeout, *popenargs, **kwargs)
    624 
    625     return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
--> 626                **kwargs).stdout
    627 
    628 

/usr/lib/python3.5/subprocess.py in run(input, timeout, check, *popenargs, **kwargs)
    706         if check and retcode:
    707             raise CalledProcessError(retcode, process.args,
--> 708                                      output=stdout, stderr=stderr)
    709     return CompletedProcess(process.args, retcode, stdout, stderr)
    710 

CalledProcessError: Command 'lsl -l' returned non-zero exit status 127

Answer 1

You should try using ;exit 0; after your command. Documentation for check_output itself says that it raises CalledProcessError if the process exits with Non zero status. Refer check_output for more details. Try the below command:

subprocess.check_output("lsl -l;exit 0;", shell=True,stderr=subprocess.STDOUT)