Febuntoo News Generator

This is my shell file

ORACLE_USER=[ORACLE_USER]
ORACLE_PASS=[ORACLE_PASS]
ORACLE_INSTANCE_NAME=[ORACLE_INSTANCE_NAME]
START_DATE=[START_DATE]
END_DATE=[END_DATE]

if
[ $START_DATE='' ]; then
START_DATE=19010101
fi

sqlplus $ORACLE_USER/$ORACLE_PASS@$ORACLE_INSTANCE_NAME @./purgingtool.sql $START_DATE $END_DATE

exit;

i want if my tag is null then it shuld take 190101 as a default value
it is happen
but now if i will give any value to START_DATE it will take 190101 as a value.

Thanks & Regards

Manish Hemnani