python subprocess not working. it is not replacing variable output

Question

I have below function which is used check ping status

def pingOk(sHost):
 try:
 output = subprocess.check_output("ping -{} 1 {}".format('n' if platform.system().lower()=="windows" else 'c', sHost), shell=True)
 except Exception, e:
 traceback.print_exc()
 return False
 return True

I tried to run the script

 pingOk(sHost)

I am getting below error:

Usage: ping [-aAbBdDfhLnOqrRUvV64] [-c count] [-i interval] [-I interface]
 [-m mark] [-M pmtudisc_option] [-l preload] [-p pattern] [-Q tos]
 [-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp_option]
 [-w deadline] [-W timeout] [hop1 ...] destination
Usage: ping -6 [-aAbBdDfhLnOqrRUvV] [-c count] [-i interval] [-I interface]
 [-l preload] [-m mark] [-M pmtudisc_option]
 [-N nodeinfo_option] [-p pattern] [-Q tclass] [-s packetsize]
 [-S sndbuf] [-t ttl] [-T timestamp_option] [-w deadline]
 [-W timeout] destination
Traceback (most recent call last):
 File "set_enviroment.py", line 54, in pingOk
 output = subprocess.check_output("ping -{} 1 {}".format('n' if platform.system().lower()=="windows" else 'c', sHost), shell=True)
 File "/usr/lib64/python2.7/subprocess.py", line 575, in check_output
 raise CalledProcessError(retcode, cmd, output=output)
CalledProcessError: Command 'ping -c 1 ' returned non-zero exit status 2

Looks like its not formatting output. Please someone help what i am doing mistake

• Pavan Kumar T S: may be due to wrong format of using ping command since its displaying ping usage help i sugget you to print the command before and validate it in terminal.
• Dev Ops Ranga: Its working fine and I tested it, it is formatting variable issue. If i use hard code values it works fine
• Pavan Kumar T S: print("ping -{} 1 {}".format('n' if platform.system().lower()=="windows" else 'c', sHost)) and check you are getting proper command
• Dev Ops Ranga: Looks like IP formatting is empty thanks Pavan

Answer 1

Since the complaint was about ping -c 1 , not ping -{} 1 {}, it's clear that the .format did happen.

Since the complaint was about ping -c 1 (note the trailing space), it's clear that the second argument to .format was an empty string.

The complaint that the command failed is presumably because ping expected a destination (hence all of the stderr complaining about usage).