subprocess.check_output() fails to return command results when pinging ip's

Question

I am trying to use subprocess module in python to ping ip addresses. Here is the code.

command = ['ping', '-c', '1', 1.1.1.1]


print((subprocess.check_output(command)).decode("utf-8"))

This would return the proper ping result for 1.1.1.1.

Ping statistics for 1.1.1.1:
    Packets: Sent = 1, Received = 1, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 4ms, Maximum = 4ms, Average = 4ms

However, if were to ping an invalid ip, like 0.0.0.0

command = ['ping', '-c', '1', 0.0.0.0]

subprocess.call(command)

print((subprocess.check_output(command)).decode("utf-8"))

Then subprocess.call(command) would return

Pinging 0.0.0.0 with 32 bytes of data:
PING: transmit failed. General failure. 

Ping statistics for 0.0.0.0:
    Packets: Sent = 1, Received = 0, Lost = 1 (100% loss)

However once the code reaches subprocess.check_output, it will not return anything and all subsequent code following it will not run. How can I have subprocess.check_output() return the full ping statement thrown by subprocess.call()?

subprocess.check_output() raises an exception if the command has a non-zero exit status. And ping returns a non-zero status if it can't ping the IP. — Barmar
– Barmar, Commented Jun 17, 2021 at 18:43
I am making sure that it will run and it does. However it will not output the result. — Skytlz
– Skytlz, Commented Jun 17, 2021 at 18:45
It runs, but when the ping fails it returns a non-zero status. — Barmar
– Barmar, Commented Jun 17, 2021 at 18:45
Why are you passing the IP addresses as (weird) numbers instead of strings? I'd have thought that's a syntax error but not in a place where I can check. — tripleee
– tripleee, Commented Jun 17, 2021 at 18:53

Barmar · Accepted Answer · 2021-06-17 18:54:19Z

1

subprocess.check_output() raises an exception if the command returns a non-zero exit status, and ping does this when it doesn't get a response to the pings.

Instead of using subprocess.call() and subprocess.check_output(), you should use subprocess.run().

command = ['ping', '-c', '1', '1.1.1.1']
print(subprocess.run(command, stdout=PIPE, stderr=STDOUT, encoding="utf-8").stdout)

answered Jun 17, 2021 at 18:54

Barmar

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