I am a newbie in bash programming. I need a bash script which can check if there is an input or not.If there is an input then continue to the second question, otherwise it will not continue unless it forces me to write the input (data). I wrote this script but is not working:

```
echo "Write buss no:"
        read bussno
        while [ true ] ; do

        if [ -z $bussno ] ; then

            echo "\Buss No. should be filled"
            read bussno

        else    

        echo "Write from date: "
             read startdate

        if [ -z $startdate ] ; then

            echo "\start date should be filled"
            read startdate

        fi

        done

```