Executing shell commands in Python

Question

I'm working in Linux/Python 3 and am creating some small scripts which consist of executing some commands inside of Python.

Example: Pinging a server

hostname= "server.com"
response= os.system("ping -c 1 " + hostname)
if response == 0:
 print (hostname, 'is up!')
else:
 print (hostname, 'is down!')

Output:

PING server.com (10.10.200.55) 56(84) bytes of data.
64 bytes from server.com (10.10.200.55): icmp_seq=1 ttl=61 time=12.4 ms
--- server.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 15.446/15.446/15.446/0.000 ms
server.com is up!

This is working OK but I don ́t need to print everything. How can I get only the first line of the output?

• Brody Critchlow: Hey are you on linux or windows?
• fr0zt: Hey there. I am in Linux
• Daniel Walker: Which version of Python 3 are you using?

Answer 1

You can use a subprocess in python3 to discard the output to devnull. Something like this

import subprocess
hostname= "server.com"
response= subprocess.call(["ping", "-c", "1", hostname], 
stdout=subprocess.DEVNULL,
stderr=subprocess.STDOUT)
if response == 0:
 print (hostname, 'is up!')
else:
 print (hostname, 'is down!')

https://docs.python.org/3/library/subprocess.html#subprocess.DEVNULL

• Maurice Meyer: check_output has no stdout flag.
• fr0zt: I get this error: raise ValueError('stdout argument not allowed, it will be overridden.') ValueError: stdout argument not allowed, it will be overridden.
• Patrick: Apologies. changed it to call. Should work now.
• fr0zt: Looks nice now. Thanks. How can I get the first line of the output for example?
• Patrick: youd have to set response= subprocess.check_output(["ping", "-c", "1", hostname]) then parse that response manually. You'd also have to use a try/except because if host is invalid it will throw an exception

Answer 2

Answer that prints the opening response as well. You may have to tweak the response if you don't want to handle it as a byte string and to handle valid but down hosts.

import subprocess
hostname= "stackoverflow.com"
try:
 response= subprocess.check_output(["ping", "-c", "1", hostname])
 print (response.split(b'\n')[0])
 print (hostname, 'is up!')
except subprocess.CalledProcessError:
 print (hostname, 'is down!')

• fr0zt: Output: b'PING stackoverflow.com (151.101.193.69) 56(84) bytes of data.' Anyway to get rid of the b' and last ', from the output?
• Patrick: you'd have to convert the byte string to a regular string. you can try wrapping it in str() but I'm not 100% on that.