Hold the output of subprocess.Popen with a arbitrary varible

Question

I'd like to retrieve the output from a shell command

In [7]: subprocess.Popen("yum list installed", shell=True)
Out[7]: <subprocess.Popen at 0x7f47bcbf6668>

In [8]: Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
Installed Packages
GeoIP.x86_64                          1.5.0-11.el7                     @anaconda
NetworkManager.x86_64  
....

The results are output to the console,

How could I hold the output to a variable saying "installed_tools"?

iBug · Accepted Answer · 2018-09-17T01:36:03.250

1

Try setting stdout and/or stderr to subprocess.PIPE.

import subprocess as sp

proc = sp.Popen("yum list installed", shell=True, stdout=sp.PIPE, stderr=sp.PIPE)

out = proc.stdout.read().decode('utf-8')
print(out)

As suggested in comments, it's better to use Popen.communicate() in case stderr needs reading and gets blocked. (Thanks UtahJarhead)

import subprocess as sp

cp = sp.Popen("yum list installed", shell=True, stdout=sp.PIPE, stderr=sp.PIPE).communicate()

out = cp[0].decode('utf-8')
print(out)

edited Sep 17 '18 at 01:36

answered Sep 16 '18 at 15:25

iBug

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Why use `proc.stdout.read()` instead of `proc.communicate()[0]`? – UtahJarhead Sep 17 '18 at 01:29
@Utah Both are OK. – iBug Sep 17 '18 at 01:30
@iBug, no, they are not both ok -- `proc.stdout.read()` will deadlock if stderr needs to be read first, which will happen if you have a significant volume of errors. – Charles Duffy Sep 17 '18 at 01:33
Thank you two. I forgot about that point. – iBug Sep 17 '18 at 01:36

Hold the output of subprocess.Popen with a arbitrary varible

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