BASH Scripting

I am trying to set the value of SIDS in the following script to
something other than "". It seems that once out of the do/done block the
value od $SIDS reverts back to ""....why is this and how can I get $SIDS
to keep its new value opnce out of the do/done block. 

# !/bin/sh
SIDS=""
grep -v '^#' /etc/oratab | while read LINE
do
      ISID=`echo $LINE | cut -f1 -d:`
      OHOME=`echo $LINE | cut -f2 -d:`
      OBOWNER=`ls -l $OHOME/bin/sqlplus | awk '{print $3}'`
      SIDS=`echo "$SIDS $OBOWNER:$ISID"`
      echo "SIDS is $SIDS"
done
      echo SIDS is  $SIDS
      echo "OBOWNER is  $OBOWNER"

the /etc/oratab file is: - 

# 
# 
LD4U:/opt/oracle/product/9.2.0:Y 
oem:/opt/oracle/product/9.2.0:Y 
ld4udev:/opt/oracle/product/9.2.0:Y 

Thanks

David