send input through stdin in python subprocess.popen

Question

I would like to start nodejs through subprocess module and send input to it but facing below error...

code:

import subprocess
def popen(self):
    cmd = "node"
    args = "--version"
    spawn = subprocess.Popen(cmd,shell=True, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
    (out,err)=spawn.communicate(args)
    print(out)
    print(err)

Result:

    [stdin]:1
--version
^

ReferenceError: version is not defined
    at [stdin]:1:1
    at Script.runInThisContext (vm.js:132:18)
    at Object.runInThisContext (vm.js:309:38)
    at internal/process/execution.js:77:19
    at [stdin]-wrapper:6:22
    at evalScript (internal/process/execution.js:76:60)
    at internal/main/eval_stdin.js:29:5
    at Socket.<anonymous> (internal/process/execution.js:198:5)
    at Socket.emit (events.js:327:22)
    at endReadableNT (_stream_readable.js:1327:12)

Expected Result:

v14.14.0

basically, i want to start node and communicate with it, send input as and when required.

Popen is chose instead of run for better control over process and shell is set to true so OS variables are considered ex. $PATH

CoderCharmander · Accepted Answer · 2020-11-22 10:16:34Z

2

This code is equivalent to you starting node, then typing --version and pressing enter. This way, node will try to interpret it as a JavaScript statement, and it does not recognize the name version. Instead, you should pass it as a command line argument:

subprocess.Popen(["node", "--version"], ...)

answered Nov 22, 2020 at 10:16

CoderCharmander

1,87812 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

ElysMech Over a year ago

thanks for reply, could you suggest how i can send input trough ’communicate()’ ? ex. send a test.js file for execution...

ElysMech Over a year ago

i guess communicate() closes the stdout, stdin and stderr once called...

CoderCharmander Over a year ago

@ElysMech Instead of communicate, you can use spawn.stdout, stdin, stderr, as regular streams.

Xiddoc · Accepted Answer · 2023-03-21 14:11:41Z

0

We can also use python oS package to run opearting system command use os package popen method and read the output using read function

import os

stream = os.popen('node --version')

output = stream.read()

print(output)

edited Mar 21, 2023 at 14:11

Xiddoc

3,6663 gold badges18 silver badges42 bronze badges

answered Nov 22, 2020 at 10:36

Surya Bhamidipati

135 bronze badges

Collectives™ on Stack Overflow

send input through stdin in python subprocess.popen

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related