Run external command from Python. Then display the output on screen and get the output simultaneously

Question

I know that it is easy to run an external command from Python and display the output on the screen. For example: (It will display the output only on the screen)

import subprocess
subprocess.Popen(['dir'])

I also know that we can run an external command from Python and get the output. For example: (It will store the output as a string in variable out and will not display the output on the screen anymore)

import subprocess
result = subprocess.Popen(['dir'], stdout=subprocess.PIPE)
out = result.stdout.read()

My question is: Is there a way to display the output on the screen and store and output in a variable simultaneously? In other words, when I run the code, the external command output will display on the screen. At the same time, a variable in the code can get the output displayed on the screen.

Update: I found out if I include stdout=subprocess.PIPE in subprocess.Popen, it will display nothing on the screen (windows command prompt).

Related questions:

live output from subprocess command

Output of subprocess both to PIPE and directly to stdout

That works. But the terminal window will open twice. The terminal window will display nothing if I store the output in `out` and the terminal window will open again to print the `out`. Note, I am executing the code in a Python script not in a command window. — Banghua Zhao, Sep 06 '17 at 18:36
Actually, I am testing in windows platform. `ls` is just for demonstration. — Banghua Zhao, Sep 06 '17 at 19:27
I found `| tee` works. The solution for windows platform is to use powershell and `| tee` — Banghua Zhao, Sep 07 '17 at 17:18

score 1 · Answer 1 · answered Sep 07 '17 at 12:49

If you need real-time output from Popen , you could use something like this (Windows platform according to your last comment):

Byte stream:

import sys, subprocess
out=b''
result = subprocess.Popen(['cmd', '/c', 'dir /B 1*.txt'], stdout=subprocess.PIPE, 
    universal_newlines=False)
for s_line in result.stdout:
    #Parse it the way you want
    out += s_line
    print( s_line.decode(sys.stdout.encoding).replace('\r\n',''))

# debugging output
print(out.decode(sys.stdout.encoding))

Text stream:

import subprocess
out=''
result = subprocess.Popen(['cmd', '/c', 'dir /B 1*.txt'], stdout=subprocess.PIPE, 
    universal_newlines=True)
for s_line in result.stdout:
    #Parse it the way you want
    out += s_line
    print( s_line.rstrip())

# debugging output
print(out)

The latter code snippet output:

>>> import subprocess
>>> out=''
>>> result = subprocess.Popen(['cmd', '/c', 'dir /B 1*.txt'], stdout=subprocess.PIPE,
...     universal_newlines=True)
>>> for s_line in result.stdout:
...     #Parse it the way you want
...     out += s_line
...     print( s_line.rstrip())
...
1.325.txt
1049363a.txt
1049363b.txt
1051416.txt
1207235log.txt
>>> print(out)
1.325.txt
1049363a.txt
1049363b.txt
1051416.txt
1207235log.txt

>>>

Thanks. But I still get nothing in the windows command prompt. If I include `stdout=subprocess.PIPE` in `subprocess.Popen`, it will always redirect and display nothing on the screen. — Banghua Zhao, Sep 07 '17 at 17:21

score 1 · Accepted Answer · answered Sep 07 '17 at 17:38

Use | tee (On windows platform, use Powershell):

import subprocess

# Run command in powershell and redirect it by | tee to a file named out.txt 
result = subprocess.Popen(['powershell', command, '|', 'tee', 'out.txt'])

# Get standard output
f = open('out.txt')
out = f.read()
f.close()

By this way, the screen will display the output on PowerShell terminal and the output will also be stored in out.

Run external command from Python. Then display the output on screen and get the output simultaneously

2 Answers2