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I want to create a script for ddwrt that pings on 4 hosts to check whether internet is available or not. If out of 4 tests, one of the ping results comes true then assume internet is working otherwise No connection. At least one of the test needs to come true.

This is the script I've been working with.

#!/bin/sh
result=`ping -c 1 8.8.8.8 | grep -c from`
sleep 10
result+=`ping -c 1 www.google.com | grep -c from` 
# I want the output from this command to add into result variable. For example, if result value is 0 then add the value of next ping command into 0, same with the rest of the commands. Is that possible?
sleep 10
result+=`ping -c 1 www.microsoft.com | grep -c from`
sleep 10
result+=`ping -c 1 www.youtube.com | grep -c from`
if [ $result -ge 1 ] 
then 
echo "Internet alright"
   logger -t 'InternetCheck' 'Internet is Connected'
   logger "ping $result"
else
    logger -t 'InternetCheck' 'After many ping tests, the Internet is not working... will apply solution'
   
   logger "ping $result"
fi

Although ddwrt already comes with watchdog, but i don't want router to reboot, instead i want to run commands at that moments to fix the issue. Please do give me any other suggestions.

Regards!

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  • What is your question? It is not clear from the OP. Please edit your question and describe in detail what you actual problem is. Commented Jun 24, 2021 at 11:15
  • Do you want a response from any of the ping tests to indicate success, or only a response from all of the ping tests to indicate success? Commented Jun 24, 2021 at 11:21
  • You don't say which issue you need to fix, but if the DD-WRT version of ping has the -w option, which makes ping more impatient, you could do this: if ping 1.2.3.4 -w 1; then echo ":-)"; else echo ":-("; fi. Commented Jun 24, 2021 at 11:33
  • Thanks everyone for replying... This was my first question here and I'm really glad that i got such lovely answers and so friendly audience. @berndbausch This also works, just needs some expanding. My question was in two parts.. Sorry i didn't know how to write it down properly. I wrote it in the code as comments.. I wanted to know can we add the output from ping -c 1 www.google.com | grep -c from into result variable by adding it to it's current value. If the result holds 0 and ping -c 1 www.google.com | grep -c from outputs 1 then final result value should be 1. Commented Jun 24, 2021 at 13:02
  • @Samantha1154: First, when replying to questions in comments, edit your original question to give the answers so that other people on the site will see it when reading the question without having to filter through the comments. Second, a ping is not a reliable way to check for network connectivity--that is not what ping was designed for, and some hosts may simply ignore ping requests (even 8.8.8.8, a well-known nameserver, may change it's policy regarding ping at any time). Can you check for a default gateway/uplink? Interface status? (more...) Commented Jun 24, 2021 at 15:02

1 Answer 1

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Some ideas:

  • ping has an exit status - 0 if it got a response, non-0 if not. You can use that instead of grepping.
  • You might want to run the 4 ping commands in parallel and use wait to wait for them. That way you don't have to wait for 4 unsuccessful pings to know that your internet connection is down.
  • Alternatively, if your connection works most of the time, you might stop after the first successful ping as you only want to know if it works, not how many destinations you can reach.

This script (only for 2 IPs and not including your logging stuff, you can extend it easily) would give an answer after a very short time (yours runs for at least 30 seconds + any ping timeouts) and return exit status 0 or 1 depending on whether a ping succeeded or all failed. It uses -W option to set a short timeout; unless your internet connection is really flaky, at least one of the addresses should return a response in less than a second.

#!/bin/sh
IP1=8.8.8.8
IP2=4.4.4.4

#start first ping, remember its pid
ping -W 1 -c 1 $IP1 >/dev/null&
PID1=$!

# start second ping, remember its pid
ping -W 1 -c 1 $IP2 >/dev/null&
PID2=$!

# wait for pings to finish
if wait $PID1
then echo $IP1 is reachable, internet is working; exit 0
fi

if wait $PID2
then echo $IP2 is reachable, internet is working; exit 0
fi

# none reachable
echo all pings failed, internet is down
exit 1
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  • Not exactly the answer i was looking for, but still Thank a lot and much simpler. This solves my problem. But can you please tell, result+=ping -c 1 www.google.com | grep -c from Will this really not work? I want the output to store into result variable by adding it to it's current value. ping -c 1 www.google.com | grep -c from produces 0 or 1 depending on internet connectivity. Commented Jun 24, 2021 at 12:56
  • in sh, += does not add but concatenate. So if 4 pings are successful, you'd get "1111" as the result, not "4". Commented Jun 24, 2021 at 13:07
  • Thanks... That cleared it up. Commented Jun 24, 2021 at 13:17

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