get syslinux hd from device name

#!/bin/bash

#get syslinux 'hd? ?' from device name (e.g. /dev/sda1) example
#use getsysl <device>

SYSL_ID=""

get_sysl_hd() #$1 - device name
{
    #get basename and check name
    T_DN=`basename $1|grep '^[sh]d[a-z][1-9]*$'`
    if [ -z "$T_DN" ]; then
        return 1
    fi

    #get letter #3
    T_3LET=`expr substr $T_DN 3 1`

    #get letter number in alphabet
    S_CODE=`printf '%d' \'$T_3LET`
    A_CODE=`printf '%d' \'a`
    SYSL_ID="hd"`expr $S_CODE - $A_CODE`

    #get volume number
    T_VOLNUM=`echo "$T_DN" | sed 's/^[a-z]*//'`
    if [ -z "$T_VOLNUM" ]; then
        T_VOLNUM=0
    fi

    SYSL_ID="$SYSL_ID $T_VOLNUM"
}

if [ -z "$1" ]; then
    echo "Use "`basename $0` "<device>"
    exit
fi

get_sysl_hd "$1"

if [ $? -ne 0 ];then
    echo "Bad device name!"
else
    echo "$1: $SYSL_ID"
fi