hi
what your name?
allrise

echo "Enter the name"
read name
FILE="/opt/name.txt"
NEW_FILE="/opt/new_name.txt"
exec 0<$FILE
    while read line
    do
     if [ -n "`echo ${line} | grep 'allrise'`" ]
     then
              echo ${line} | sed 's|allrise|hello $name|g' >>$NEW_FILE
     else
             echo $line >>$NEW_FILE
     fi
     done <$FILE

hi
what your name?
hello $name

hi
what your name?
hello john