splitter() {
   a=$1; s=$2; l=$3; r=$4;
   mid=$(expr ${#a[*]} / 2);
   echo $s ${a[*]:0:$mid} > $l
   echo $(($mid + $s)) ${a[*]:$mid} > $r
}

bsearch() {
   (to=$1; read s arr; a=($arr);
       test  ${#a[*]} -gt 1  && (splitter $a $s >(bsearch $to) >(bsearch $to)) || (test "$a" -eq "$to" && echo $a at $s)
   )
}

binsearch() {
   (read arr; echo "0 $arr" | bsearch $1)
}

echo "1 2 3 4 6 7 8 9"  | binsearch 6