bash - Testing empty variables -

i have large number of variables in script, , want script error out if 1 of variables empty.

i know can:

if [[ -z "$var_1" ]] || [[ -z "$var_2" ]] || ... [[ -z "$var_n" ]];   # failure message fi 

however, cannot inform user variable empty if in way. there alternative approach above can inform user empty variable?

#!/bin/sh foo=(var_1 var_2 var_n)  bar in ${foo[*]}   if [[ ! ${!bar} ]]       echo $bar empty   fi done