@Mouli This is one of the beauties of
awk: an entire record (here: a line) is referred to as $0; it is composed of the different fields into which it is automatically split based on the input field separator: $1, $2, etc. By assigning to $6, we update both $6 and $0, and $0 is what is eventually output by the print statement (print without arguments means print $0). So everything that is not explicitly updated simply remains the same.