CODEWITHSUNDEEP
pythonlinuxos.system
Sid
Sid

Reputation: 11

os.system giving weird output in linux

I am running this python function in suse linux to grep ip of node from /etc/hosts--

def mm_node():
    import os
    node_name = os.system("`cat /etc/hosts | egrep -i mm | grep om | awk '{print $1}'`")
    return node_name

mm_node()

As a result, it is showing this weird output

sh: 192.168.10.10: command not found

instead of

192.168.10.10

If I run the shell command

(cat /etc/hosts | egrep -i mm | grep om | awk '{print $1}')

directly on linux command prompt, it gives the o/p as

192.168.10.10

Upvotes: 0

Views: 217

Answers (2)

user4815162342
user4815162342

Reputation: 155505

Backquotes tell the shell to capture the output and use it on the command line, typically as argument to a command, as in grep `whoami` /etc/passwd. In your case the command line consists only of a backquoted pipeline, so the shell interprets the output of the pipeline as the command to execute. That is why it complains that the IP address is "not found".

If your intention is to capture the output of the pipeline to use in your Python code, you should use the subprocess module, which is the modern alternative to os.system that allows easy capturing of the output. For example:

import subprocess

def mm_node():
    output = subprocess.run(
        "cat /etc/hosts | egrep -i mm | grep om | awk '{print $1}'",
        shell=True,
        capture_output=True
    ).stdout
    return output.strip()

print(mm_node())

Upvotes: 2

Morteza Soltanabadiyan
Morteza Soltanabadiyan

Reputation: 638

def mm_node():
    import os
    node_name = os.system("cat /etc/hosts | egrep -i mm | grep om | awk '{print $1}'")
    return node_name

mm_node()

Upvotes: 0

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