Create a backup of a file and try NOT to overwrite any previous backups. Also make sure not to create unnecessary backups in case the files are identical.

backup.sh

backup() {
    f=$1
    bkp=$f.bkp
    index=1

    while true; do
        # Make sure NOT TO OVERWRITE a bkp file!!!
        if [[ -f "$bkp.$index" ]]; then
            prevBkp="$bkp.$index"
            index=$((index+1))
            continue
        fi

        bkp=$bkp.$index

        copy=y

        # Avoid making unnecessary backups.
        if [[ $prevBkp != "" ]]; then
            file1=`md5sum -b $f | cut -f 1 -d " "`
            file2=`md5sum -b $prevBkp | cut -f 1 -d " "`
            if [[ "$file1" == "$file2" ]]; then
                copy=n
            fi
        fi

        if [[ $copy == "y" ]]; then
            cp $f $bkp
        fi

        break
    done
}