Sync folder with Google Drive. Recursively downloads with wget and Google Drive public links. Used to sync ebooks to my eReaders (Kobo). Be warned that public links are dangerous as they could allow someone to download your files. Be sure to use this only in secure environments. This has been tested to be used in POSIX shells as well as in bash.

sync.sh

#!/bin/sh

#input sharelink here. Example: https://drive.google.com/folderview?id=0B1g-MbiD2F6vdtOT92b3MoerO&usp=sharing
SHARELINK="https://drive.google.com/folderview?id=idU&usp=sharing"
DESTINATION="/full/path/to/folder"
# Change following to false when you don't want to delete files when they are missing from google drive. This can
REMOVEFILES=true 

# Begin code

download () {
	url=$1
	folder=$2
	changed=$3

	wgetoutput="`wget --no-check-certificate -qO- $url 2>&1`"
	mkdir -p "$folder"
	commands="$(echo "$wgetoutput" | grep -Eo '\[,,\"(.*?)\",,,,,\"(.*?)\"')"
	missingfiles="$(find "$folder" -type f -depth 1 -print)"
	missingdirectories="$(find "$folder" -type d -depth 1 -print)"

	#Go to next

	subfolders="$(echo "$wgetoutput" | grep -Eo '\[,".*?\",\".*?folder' | cut -c 4- | cut -d\" -f 1)"
	IFS="
"
	for subfolder in $subfolders; do
		name=$(echo "$wgetoutput" | grep -Eo 'entry-'$subfolder'.*?</div></div><div class=\"flip-entry-title\">(.*?)</div>' | grep -Eo 'entry-title">.*?</div>$' | cut -c 14- | sed 's/<\/div>//')
		newdest="$2/$name"
		escapedfile="$(echo "$newdest" | sed -e 's/[]\$*.^|[]/\\&/g')"
		missingdirectories=$(echo "$missingdirectories" | sed -e "s@$escapedfile@@g" | sed '/^$/d')
		output=$(download "https://drive.google.com/folderview?id=$subfolder&usp=sharing" "$newdest" $changed)
		changed=$output
	done

	#Download files
	echo "Downloading for $folder..." 1>&2;
	for line in $commands; do
		id=$(echo "$line" | grep -Eio '\"[0-9a-z]+-[0-9a-z]+\"' | cut -c 2- | sed s'/.$//')
		name=$(echo "$line" | sed -e 's/\[,,\"//' | sed s/\".*//'')
		file="$folder/$name"
		cmd=$(echo "wget --no-check-certificate -nc -q --no-cookies -O \"$file\" \"https://docs.google.com/uc?export=download&id="$id"\"")
		eval "$cmd"
		commandresult=$?
		if [ "$commandresult" -eq 0 ]; then 
			echo "Downloaded: $file" 1>&2;
			changed=$(($changed + 1))
		else 
			echo "Skipped (Already exists or error): $file" 1>&2;
		fi
		escapedfile=$(echo "$file" | sed -e 's/[]@$*.^|[]/\\&/g')
		missingfiles=$(echo "$missingfiles" | sed 's@'$escapedfile'@@g' | sed '/^$/d')
	done
	echo "Finished downloading!" 1>&2;

	#Remove missing files
	if [ $REMOVEFILES = true ]; then
		echo "Checking files to remove from $folder..." 1>&2;
		i=0
		for line in $missingfiles; do
				echo "Removing file: $line" 1>&2;
				rm -f "$line"
				changed=$(($changed + 1))
		done
		for line in $missingdirectories; do
				echo "Removing directory: $line" 1>&2;
				rm -rf "$line"
				changed=$(($changed + 1))
		done
		echo "Finished scan!" 1>&2;
	fi

	echo $changed
}

result=$(download "$SHARELINK" "$DESTINATION" 0)
echo "Changed: $result files/folders"
if [ $result -ne 0 ]; then
	echo "Sync made changes to disk!"
fi

I tried to run this script but I'm getting the below error.

find: warning: you have specified the -depth option after a non-option argument -type, but options are not positional (-depth affects tests specified before it as well as those specified after it). Please specify options before other arguments.

This error I could fix moving -depth 1 to before -type. Now, I'm got a error find: paths must precede expression: '1'.