[dladm show-dev -s -i <interval> <device>] Can not output logs

Hello
I am trying to get Network throughput logfile using shell script(/bin/sh)
  [dladm  show-dev -s -i <interval> <device>] command

My system is
SunOS hostname 5.10 Generic_127128-11 i86pc i386 i86pc

----------------------------------------------
<shell script abstract>
for i in ${NIC}
do
  dladm show-dev -s -i ${INTERVAL} ${i} >>${LOG_DIR}/dladm_${i}_${DATE}.log &
done
---------------------------------------------

 This command was derived from an article in the Oracle Blog.(Japanese Site)
 https://blogs.oracle.com/yappri/entry/network_analysis


Case of
 command interval ${INTERVAL}= 1 second is All right

But the other cases
 command interval ${INTERVAL}> 1 seconds are not working...

Please tell me how to get logs of dladm command.