A simple backup script.

backer.sh

#!/bin/bash
# AUTHOR
#	2013/10/08  Nobu C. Shirai
#	2018/10/06  Akira Hasegawa

backer(){
	check_options $@
	Ind=1
	for TargetFile in ${ArgFiles[@]}
	do
		echo "[${Ind}] $TargetFile"
		if [ ! -f "$TargetFile" ]; then
			echo "$TargetFile does not exist"
			break
		fi
		setBackDir "$TargetFile"

		# Set NewBackFile and OldBackFile
		prefix_no="$(( $( find "${BackDir}" -regex ".*/[0-9][0-9]*_${FileName}" | wc -l ) ))"
		NewBackFile="${prefix_no}_${FileName}"
		OldBackFile=""
 		if [ $prefix_no != 0 ]; then
			OldBackFile="$(( prefix_no - 1 ))_${FileName}"
 		fi

		# Backup TargetFile as $BackDir/$NewBackFile
 		diff -q "$TargetFile" "$BackDir/$OldBackFile" 1>/dev/null 2>&1
		if [[ $? != 0 ]]; then
			cp -vp "$TargetFile" "$BackDir/$NewBackFile"
		else
			echo " This file had already backuped. ($OldBackFile)"
		fi
	((Ind++))
	done
}

check_options(){
usage_msg="\
Usage: $0 [options] files

Options:
  -h		show this help
  -d dir	select PATH to backup (default is current directory)
  -c		make backups at current directory
"
	
	TargetDir=""
	while getopts hd:c option
	do
		case "$option" in
		h)
			echo "$usage_msg"
			exit 0
			;;
		d)
			TargetDir="$OPTARG"
			if [ -d "$OPTARG" ]; then
				echo "TargetDir = $OPTARG" 
			else
				echo "$OPTARG does not exist."
				exit 1
			fi
			;;
		c)
			TargetDir="."
			;;
		\?)
			echo "Usage: $0 [-h] [-d dir] files" 1>&2
			exit 1;;
		esac
	done
	shift `expr "$OPTIND" - 1`
	ArgFiles=($@)
	if [ ${#ArgFiles} = 0 ]; then
		echo "$usage_msg"
		exit 1
	fi
	if [ -d "$TargetDir/Back" ]; then
		TargetDir="$TargetDir/Back"
	elif [ -d "$TargetDir/back" ]; then
		TargetDir="$TargetDir/back"
	elif [ -d "$TargetDir/BACK" ]; then
		TargetDir="$TargetDir/BACK"
	else
		TargetDir="$TargetDir"
	fi
}

setBackDir(){
	file="$1"
	slash_count=`echo $file | grep -c "/"`
	if [[ $slash_count != 0 ]]; then
		FileDir="${file%/*}"
	else
		FileDir="."
	fi
	FileName="${file##*/}"
	BackDirName="${FileName}.dir"
	if [ "$TargetDir" = "" ]; then
		if [ -d "$FileDir/Back" ]; then
			BackDir="$FileDir/Back/$BackDirName"
		elif [ -d "$FileDir/back" ]; then
			BackDir="$FileDir/back/$BackDirName"
		elif [ -d "$FileDir/BACK" ]; then
			BackDir="$FileDir/BACK/$BackDirName"
		else
			BackDir="$FileDir/$BackDirName"
		fi

	else
		BackDir="$TargetDir/$BackDirName"
	fi
	mkdir_idne $BackDir
}

mkdir_idne(){
	if [ ! -d $1 ]; then
		mkdir $1
		echo "---> $1 was created."
	fi
}

backer $@