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

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.