#set "default" parameter
query=""

while [ "$1" != "" ]; do
    case $1 in
        -q | --query )          shift
                                query=$1
                                ;;
    esac
    shift
done

#query cannot be empty
if (($query == ""))
then
 echo 'no query'
 exit
fi

echo "query - $query"

./script.sh -q request

query - request

./script.sh -q

./script.sh

./main.sh: line 13: ((: == : syntax error: operand expected (error token is "== ")

query -

if [ "$query" == "" ]

if [ -z "$query" ]