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#!/bin/bash
###################################################################################################
# check-internet-connectivity
###################################################################################################
# Copyright 2017-2022 Jean-Christophe Manciot <jcmanciot@sdxlive.com>
#
# Licensed under a GPLv3 License; you may not use this file except in compliance with the License. 
# You may obtain a copy of the License at
#
#    https://www.gnu.org/licenses/gpl-3.0.md
#
# The licensor cannot revoke these freedoms as long as you follow the license terms.
#
# Attribution — You must give appropriate credit, provide a link to the license, and indicate if 
#               changes were made. You may do so in any reasonable manner, but not in any way that 
#               suggests the licensor endorses you or your use.
###################################################################################################

###################################################################################################
#
# Checking whether the Internet connectivity is OK or not.
#
###################################################################################################
#
# Requirements:
# ------------
#
# - We assume that wget package is already installed.
#
###################################################################################################
#
# Parameters:
# ----------
#
###################################################################################################
#
# Returned values:
# ---------------
#
# - 0: Internet is OK (online)
# - 1: Internet is KO (offline)
#
###################################################################################################
#
# Usage example:
# -------------
#
# check-internet-connectivity
#
###################################################################################################
if [[ $LOG_CHECK_INTERNET_CONNECTIVITY == ON ]]; then
        # Getting the last existing file descriptor of ~/.drive-google/logs/drive-google.log
        fd=$(ls -al /proc/$$/fd | grep ~/.drive-google/logs/drive-google.log | sed -E 's|^.* ([0-9]+) -> .*$|\1|g' | sort -V | tail -n 1)

        # Case where fd is unset, i.e the file ~/.drive-google/logs/drive-google.log has not yet been opened
        if [[ -z $fd ]]; then
                lowest_unused_fd () 
                {
                        local fd=0
                        while [ -e /proc/$$/fd/${fd} ]; do
                                fd=$((fd+1))
                        done
                        echo $fd
                }
                fd=$(lowest_unused_fd)

                # Opening ~/.drive-google/logs/drive-google.log as file descriptor $fd for appending
                eval "exec $fd>> ~/.drive-google/logs/drive-google.log"
        fi

        # Writing the trace output generated when set -x is enabled to file descriptor $fd 
        eval "BASH_XTRACEFD=$fd"
        # Logging line numbers - We could also use ${0} for ${BASH_SOURCE}
        BASH_SOURCE_BASENAME=$(basename ${BASH_SOURCE})
        export PS4='${BASH_SOURCE_BASENAME}.${LINENO}+ '
        # Expanding all variables and prints the full commands before output of the command
        set -x
fi

wget -q --spider https://www.google.com

echo $?