/bin/sh variable pass out of pipe

I have a small shell script to try to pass variable out of pipe and function.

#!/bin/sh
dir_names=

level2_dir_except_list="/bin /cdrom /dev /devices /fallback /kernel /lib /lost+found /mnt /net /proc /sbin /var /vol"

get_level2_dir()
{
    export dir_names
    find /*/. \( -type d -a  -name . -prune \) | {
        export dir_names
        while read line
        do
            except_flag="false"
            dir_name=`echo $line | cut -f1-2 -d"/"`
            for except_dir in ${level2_dir_except_list}
            do
                if [ "$dir_name" = "$except_dir" ]
                then
                    except_flag="true"
                    break
                fi
            done

            if [ "$except_flag" != "true" ]
            then
                dir_names="$dir_names $dir_name"
            fi
        done

        echo $dir_names  # This one is fine
     }

     echo $dir_names  # empty string
}

get_level2_dir
echo $dir_names #empty string

Also is there better way to do it?
~
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