while read定位行, sed删除并增加新行

#!/bin/bash
#在test.html中插入aaaaa

installsir="11111"
FILE_NAME="test.html"

TB_START=""
TB_END=""
TB_STR=

exec 3<> $FILE_NAME
while read LINE <&3
do
    if [ "$LINE" == "$TB_END" ]
    then
        TB_STR=`echo $LINE`
    fi  
done
exec 3>&-

if [ "$TB_STR" == "$TB_END" ]
then
    echo "go"
    sed  -i '/<\/table>/d' $FILE_NAME
    echo "  "$installsir"">>$FILE_NAME
    echo "$TB_END">>$FILE_NAME
fi

#test.html
#
#    0000
#