子进程不捕获 stdout 的输出，将其存储在 Python 中的变量中

Question

I tried the below code to capture the output from screen using the sub-process, but its not doing what I intended to do.

#!/tools/bin/python

import subprocess

result = subprocess.check_output("echo $USERNAME", shell=True)
print result

expected output is:

vimo 
vimo 

ie one for the echo process and one for printing the result output. But what I see is

vimo

But when I try to print the result output, its always empty.

What am I missing in the above puzzle !! Help out !!

Answer 1

Here you goes some greatly stripped (and altered for privacy reasons) raw dummy piece of code, grabbing both stdin and stdout from external script output.

from subprocess import Popen, PIPE

cmd = ['echo', 'foo']

proc = Popen(cmd, stdout=PIPE, stderr=PIPE)
comm = proc.communicate()

if proc.returncode != 0:
    # code to handle / parse stderr (comm[1])
    raise RuntimeError(
        '\'%s\': command has failed (%d):\n%s'
        % ('some value', proc.returncode, comm[1]))

for line in comm[0].split('\n'):
    if line.find('Wrote:') == 0:
        # some code to parse stdout
        pass

Answer 2

Python >= 3.7 (tested with Python 3.9)

r=subprocess.run(['echo','$XDG_DATA_HOME'],capture_output=True,shell=True)
assert r.stdout.find(b'share')>0 # ERROR
r=subprocess.run('echo $XDG_DATA_HOME',capture_output=True,shell=True)
assert r.stdout.find(b'share')>0 # OK