Set Oracle environment Variable with shell script !!

[dbasupuser]

I have the following script which doesn't work as suppose to any ideas what;s wrong ??

cat setenv.sh

if [ -t 0 ]                             # Command executed from a terminal
then
        ORACLE_SID=""
        while [ -z "${ORACLE_SID}" ]
        do
                tput clear; tput rev
                echo "Valid Oracle SIDs are :"
                tput rmso
                for SID in `cat /etc/oratab|grep -v "^#"|cut -f1 -d: -s`
                do
                        echo "                  ${SID}"
                done
                DEFAULT=`cat /etc/oratab|grep -v "^#"|cut -d: -f1 -s|head -1`
                echo "\nEnter the Oracle SID you require (def: $DEFAULT): \c"
                read ANSWER
                [ "${ANSWER}" = "" ] && ANSWER=$DEFAULT
                export ORACLE_SID=`grep "^${ANSWER}:" /etc/oratab|cut -d: -f1 -s`
                export ORACLE_HOME=`grep "^${ANSWER}:" /etc/oratab|cut -d: -f2 -s`
                if [ "${ORACLE_SID}" = "" ]
                then
                        echo "\n\n              ${ANS}: Invalid Oracle SID  \c"
                        sleep 2
                fi
        done
else                                    # Set to first entry in oratab
        export ORACLE_SID=`cat /etc/oratab|grep -v "^#"|cut -d: -f1 -s|head -1`
        export ORACLE_HOME=`cat /etc/oratab|grep -v "^#"|cut -d: -f2 -s|head -1`
fi

export ORACLE_SID=$ORACLE_SID
export ORACLE_HOME=$ORACLE_HOME
export PATH=${PATH}:${ORACLE_HOME}/bin
#ORAENV_ASK=NO
#. ${ORACLE_HOME}/bin/oraenv
#ORAENV_ASK=
echo
echo Oracle SID is now `tput rev`$ORACLE_SID`tput rmso`, Oracle Home is `tput rev`$ORACLE_HOME`tput rmso`
echo

I am reading the oratab and asking for which sid to set to and then export ORACLE_SID and ORACLE_HOME based on input.
It does set the SID and HOME inside the script but when I echo it shows the default values. Any reason ????

./setenv.sh

Valid Oracle SIDs are :
                        mdmop
                        mdmt
                        mdmp

Enter the Oracle SID you require (def: mdmop): mdmt

Oracle SID is now mdmt, Oracle Home is /u001/app/oracle/product/9.2/home


 ga016dhd -> echo $ORACLE_SID
mdmop                                <== Not really set to mdmt(even if it said it is)
 ga016dhd -> echo $ORACLE_HOME
/u001/app/oracle/product/9.2/home
 [/home/oracle/script - oracle]

[LKBrwn_DBA]

You need to execute the script as: dot, space, setenv.sh:

. setenv.sh