Let your computer tell you when your internet is back on. Bash script that requires cron and espeak.

checkinternet.sh

#!/bin/bash
# Requires: espeak, crontab, mktemp.
#
# Script for checking if this computer is connected to internet.
# If you copy it to $installdir, give this script execution permission.
# And remember to set proper ownership (using chown).
# Use Example:
#
#  sudo chmod +x checkinternet.sh
#  sudo cp checkinternet.sh /usr/local/sbin/
#  sudo chown user:group /usr/local/sbin/checkinternet.sh
#  checkinternet.sh --install
#
# Warning: this script was made using `man`, because I had no Internet.
#

testaddress="8.8.8.8"
thisfilename="checkinternet.sh"
installdir="/usr/local/sbin"

usage() {
    if [ "$1" = -h ]
    then
	exec 1>&2
	echo -n U
    else
	echo -n u
    fi

    echo "sage: `basename $0` [ --install | --uninstall | --statefile name | --check ] [ -h, --help ]"

    if [ "$1" = -h ]
    then
	cat <<EOF

Options: --install          add cron entry for check internet each 5 min.
         --uninstall        remove cron entries from this script.
         -h, --help         print this help and exit
	     --statefile name   give a file for check and save state.
         --check            check for internet connection now. 
EOF
	exit 0
    else
	exit 1
    fi
}

if [ "$#" -eq 0 ]
  then
    usage
fi

while [ $# -ne 0 ]
do
    case "$1" in
	-v|--version)
	    echo "`basename $0` version 1.0" \
		"by Erico Porto <http://github.com/ericoporto>"
	    exit 0
	    ;;
	-h|--help)
	    usage -h
	    ;;
	--statefile)
	    test $# -gt 1 || usage
	    tempbool="$2"
        shouldcheck=1
	    shift
	    ;;
	--install)
	    install=1
        shouldcheck=0
	    ;;
	--uninstall)
	    uninstall=1
        shouldcheck=0
	    ;;
	--check)
	    shouldcheck=1
	    ;;
	*)
	    usage
	    ;;
    esac
    shift
done

if [[ $uninstall ]] ; then
    crontab -l | while read -r; do
        [[ $REPLY = *$thisfilename* ]] && continue
        printf '%s\n' "$REPLY"
    done | crontab -
    echo " "
    echo "removed entries from cron"
    echo " "
    exit
else
    if [[ $install ]] ; then
        tmpbool=`mktemp -t hasinternet.XXX` 
        echo "0" > $tmpbool 

        #let's make a new crontab
        crontab -l | while read -r; do
            [[ $REPLY = *$thisfilename* ]] && continue
            printf '%s\n' "$REPLY"
        done | crontab -

        newcronfile=`mktemp -t new.cronfile.XXX` 

        crontab -l > $newcronfile

        printf "\n...adding to cron...\n"
        #echo new cron into cron file
        echo "*/5 * * * * $installdir/$thisfilename --statefile $tmpbool"  >> $newcronfile

        #install new cron file
        crontab $newcronfile

        #remove new cron file
        rm $newcronfile

        #say success
        printf "\nInstalled!\nkeep this computer on.\n\n"
        exit
    fi
fi

if [[ $shouldcheck -eq 1 ]]; 
then 
    hasntpinged=`ping -c 3 -W 3 $testaddress | grep \ 0\ received`
    if [[ $tempbool ]]; then
        isbooltrue=`cat $tempbool | grep 1`
        isboolfalse=`cat $tempbool | grep 0`

        if [[ $hasntpinged ]]; then
            if [[ $isbooltrue ]]; then 
                echo "didn't pinged"
                espeak "internet connection lost."

                echo "0" > $tempbool 
            fi
        else
            if [[ $isboolfalse ]]; then 
                echo "has pinged"
                espeak "connected to internet!"

                echo "1" > $tempbool
            fi
        fi

    else

        if [[ $hasntpinged ]]; then
            echo "didn't pinged"
            espeak "no internet here."
        else
            echo "has pinged"
            espeak "we have internet!"
        fi

    fi
fi