字符串按長度截斷

#!/bin/sh

function split() {
    raw=$1
    length=`expr ${#raw}`

    if [ `expr $length % 2` -ne 0 ]; then
        raw="0"$raw
        length=`expr $length + 1`
    fi

    for i in $(seq `expr $length / 2`); do
        idx=`expr $i - 1`
        offset=`expr $idx \* 2`
        bytes[i-1]=${raw:$offset:2}
    done
}

split $1
echo ${bytes[@]}
echo ${#bytes}

爲什麼${#bytes}返回的總是2？？