shell split string

Method 1

#!/bin/sh
# for usb auto suspend , triggered by usb insert
stringK=$1
i=1
seg="1-1"
while [ -n "$seg" ]
do
  if [ "$i" -eq "1" ]; then
    stringU=$seg
  else
    stringU=$stringU"."$seg
  fi
  if [ -d /sys/bus/usb/devices/$stringU ]; then
....
  fi
  let "i+=1"
  seg=`echo $stringK $i|                               
  awk '{ split($1,list,"."); print list[$2] }'`
done
exit 0

Method 2

#!/bin/bash
A=1-1.2.4:1.0
IFS=:
B=($A)
echo $B
while [ "$B" != "${B%.*}" ] ; do
   B=${B%.*}
   echo $B
done