How to check internet access using bash script in linux?

Question

In my school, the internet is not available(every night after 23:0 the school will kill the internet, to put us in bed >..<), then the ping will never stop, though I have use

Answer 1

Install fping: > less problem then ping.

fping google.com | grep alive

to use for example like:

#!/bin/bash

itest=$(fping google.com | grep alive)

while [ "$itest" == "" ] 
        do
        sleep 5
        itest=$(fping google.com | grep alive)
done
echo now online

Answer 2

If the school actually turns off their router instead of redirecting all traffic to a "why aren't you in bed" page, then there's no need to download an entire web page or send HTTP headers. All you have to do is just make a connection and check if someone's listening.

nc -z 8.8.8.8 53

This will output "Connection to 8.8.8.8 port 53 [tcp/domain] succeeded!" and return a value of 0 if someone's listening.

If you want to use it in a shell script:

nc -z 8.8.8.8 53  >/dev/null 2>&1
online=$?
if [ $online -eq 0 ]; then
    echo "Online"
else
    echo "Offline"
fi

Answer 3

I decided to combine a few of the above so I could later create a plot showing ups, downs, and their durations:

#!/bin/bash
#
# pinger is a bash shell script that monitors the network 
# status every 15 seconds and records if it is up '1' or down '0'
# into the file log.csv from whence it may be plotted.
#
# author: J. W. Wooten, Ph.D.
# since: 11/12/2019
# version: 1.0
#
TIMESTAMP=`date +%s`
while [ 1 ]
  do
    nc -z -w 5 8.8.8.8 53  >/dev/null 2>&1
online=$?
    TIME=`date +%s`
    if [ $online -eq 0 ]; then
      echo "`date +%Y-%m-%d_%H:%M:%S_%Z` 1 $(($TIME-$TIMESTAMP))" | tee -a log.csv
    else
      echo "`date +%Y-%m-%d_%H:%M:%S_%Z` 0 $(($TIME-$TIMESTAMP))" | tee -a log.csv
    fi
    TIMESTAMP=$TIME
    sleep 15
  done;

this outputs to a csv file every 15 seconds. Using Excel or Numbers, you can read the file and create a plot which will show when internet was not available and also the duration. If it changes from your sleep interval, then it is spending time trying to connect. Hope to add the ability to send me a text when it detects network is down next. Thanks to all above.

Answer 4

Using the example above, I wrote this script to log the state of your connection: https://gist.github.com/cganterh/ffc2fffa8263857cbece

First, save the following code into a name.sh file.

#!/bin/bash

while true
do
    wget -q --tries=10 --timeout=20 -O - http://google.com > /dev/null
    if [[ $? -eq 0 ]]; then
        echo $(date) "1" | tee -a log.csv
    else
        echo $(date) "0" | tee -a log.csv
    fi
    sleep 5
done

Then, execute name.sh file in terminal, then check the log state information in log.csv of the same folder.