[bash] Checking host availability by using ping in bash scripts

I want to write a script, that would keep checking if any of the devices in network, that should be online all day long, are really online. I tried to use ping, but

if [ "`ping -c 1 some_ip_here`" ]
then
  echo 1
else
  echo 0
fi

gives 1 no matter if I enter valid or invalid ip address. How can I check if a specific address (or better any of devices from list of ip addresses) went offline?

You don't need the backticks in the if statement. You can use this check

if ping -c 1 some_ip_here &> /dev/null
then
  echo 1
else
  echo 0
fi

The if command checks the exit code of the following command (the ping). If the exit code is zero (which means that the command exited successfully) the then block will be executed. If it return a non-zero exit code, then the else block will be executed.

There is advanced version of ping - "fping", which gives possibility to define the timeout in milliseconds.

#!/bin/bash
IP='192.168.1.1'
fping -c1 -t300 $IP 2>/dev/null 1>/dev/null
if [ "$?" = 0 ]
then
  echo "Host found"
else
  echo "Host not found"
fi

for i in `cat Hostlist`
do  
  ping -c1 -w2 $i | grep "PING" | awk '{print $2,$3}'
done

FYI, I just did some test using the method above and if we use multi ping (10 requests)

ping -c10 8.8.8.8 &> /dev/null ; echo $?

the result of multi ping command will be "0" if at least one of ping result reachable, and "1" in case where all ping requests are unreachable.

I liked the idea of checking a list like:

for i in `cat Hostlist`
do  
  ping -c1 -w2 $i | grep "PING" | awk '{print $2,$3}'
done

but that snippet doesn't care if a host is unreachable, so is not a great answer IMHO.

I ran with it and wrote

for i in `cat Hostlist`
do
  ping -c1 -w2 $i >/dev/null 2>&1 ; echo $i $?
done

And I can then handle each accordingly.

I can think of a one liner like this to run

ping -c 1 127.0.0.1 &> /dev/null && echo success || echo fail

Replace 127.0.0.1 with IP or hostname, replace echo commands with what needs to be done in either case.

Code above will succeed, maybe try with an IP or hostname you know that is not accessible.

Like this:

ping -c 1 google.com &> /dev/null && echo success || echo fail

and this

ping -c 1 lolcatz.ninja &> /dev/null && echo success || echo fail

This seems to work moderately well in a terminal emulator window. It loops until there's a connection then stops.

#!/bin/bash

# ping in a loop until the net is up

declare -i s=0
declare -i m=0
while ! ping -c1 -w2 8.8.8.8 &> /dev/null ;
do
  echo "down" $m:$s
  sleep 10
  s=s+10
  if test $s -ge 60; then
    s=0
    m=m+1;
  fi
done
echo -e "--------->>  UP! (connect a speaker) <<--------" \\a

The \a at the end is trying to get a bel char on connect. I've been trying to do this in LXDE/lxpanel but everything halts until I have a network connection again. Having a time started out as a progress indicator because if you look at a window with just "down" on every line you can't even tell it's moving.

up=`fping -r 1 $1 `
if [ -z "${up}" ]; then
    printf "Host $1 not responding to ping   \n"
    else
    printf "Host $1 responding to ping  \n"
fi

This is a complete bash script which pings target every 5 seconds and logs errors to a file.

Enjoy!

#!/bin/bash
        
        FILE=errors.txt
        TARGET=192.168.0.1

          touch $FILE
          while true;
          do
            DATE=$(date '+%d/%m/%Y %H:%M:%S')
            ping -c 1 $TARGET &> /dev/null
            if [[ $? -ne 0 ]]; then
              echo "ERROR "$DATE
              echo $DATE >> $FILE
            else
              echo "OK "$DATE
            fi
              sleep 5
          done