Send input (command) with communicate to created Subprocess Python

Question

I have created a Subprocess object. The subprocess invokes a shell, I need to send the shell command provided below to it. The code I've tried:

from subprocess import Popen, PIPE

p = Popen(["code.exe","25"],stdin=PIPE,stdout=PIPE,stderr=PIPE)
print p.communicate(input='ping 8.8.8.8')

The command doesn't execute, nothing is being input into the shell. Thanks in advance.

Have you checked the stderr of your process? – Chen A. Nov 03 '17 at 11:02 — Chen A., Nov 03 '17 at 11:02
Yes it is empty at all.I think – Ruse Bolton Nov 03 '17 at 11:03 — Ruse Bolton, Nov 03 '17 at 11:03
So your code.exe spawns a shell? – Milan Velebit Nov 03 '17 at 11:08 — Milan Velebit, Nov 03 '17 at 11:08
Yes, it spawns the shell – Ruse Bolton Nov 03 '17 at 11:13 — Ruse Bolton, Nov 03 '17 at 11:13
Wait, why are you printing the p.communicate function? – Milan Velebit Nov 03 '17 at 11:14 — Milan Velebit, Nov 03 '17 at 11:14
I see the output in this way – Ruse Bolton Nov 03 '17 at 11:15 — Ruse Bolton, Nov 03 '17 at 11:15

score 1 · Answer 1 · answered Nov 04 '17 at 10:52

If I simulate code.exe to read the arg and then process stdin:

#!/usr/bin/env bash
echo "arg: $1"
echo "stdin:"
while read LINE
do
  echo "$LINE"
done < /dev/stdin

and slightly update your code:

import os
from subprocess import Popen, PIPE

cwd = os.getcwd()
exe = os.path.join(cwd, 'foo.sh')
p = Popen([exe, '25'], stdin=PIPE, stdout=PIPE, stderr=PIPE)
out, err = p.communicate(input='aaa\nbbb\n')
for line in out.split('\n'):
    print(line)

Then the spawned process outputs:

arg: 25
stdin:
aaa
bbb

If input is changed without a \n though:

out, err = p.communicate(input='aaa')

Then it doesn't appear:

arg: 25
stdin:

Process finished with exit code 0

So you might want to look closely at the protocol between both ends of the pipe. For example this might be enough:

input='ping 8.8.8.8\n'

Hope that helps.

Why does my subprocess die after I communicate with it once? In the second time it say: you're writing to a closed file. — Alex Deft, Jun 24 '19 at 19:34
If you submit a question showing your code it will be easier to answer. Ideally, you have logging in your child process to explain why it terminates. — mjr104, Jun 26 '19 at 05:29

Send input (command) with communicate to created Subprocess Python

1 Answers1