Krdytkyu

I try to implement positional parameters in bash script and check them, but have some issue in if/then switch statement.

Script:

#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"

All works well when I set the correct parameters:

$ ./script.sh -q request

query - request

-q parameter cannot be empty and I need to validate it. So, when the command line looks like:

$ ./script.sh -q

or

$ ./script.sh

I get this error:

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

query - 

How to correctly implement if operator in this case?

(( ... )) is for arithmetic evaluation.

You should use [ ... ] (just like you did in the while condition) or bash's extended test syntax [[ ... ]] - and remember to quote "$query" and leave whitespace around the [ and ] operators:

if [ "$query" == "" ]

Alternatively, use the -z empty string test:

if [ -z "$query" ]

For general help with questions like this, try www.shellcheck.net or install the shellcheck package from the universe repository.