in reply to to copy certain content in file & repeat it .
Dude.... that is like the absolutely worst explanation ever. Did you proof read it at all?
Where's your code? What have you tried thus far? I know what I mean. Why don't you?
If all you care about is doubling one section of content then you could just read the entire file into a variable and then use a regex. The biggest challenge is determining what the regex should match, and we can't tell you that given the limitted information that you've provided.
$contents =~ s/(match me)/$1$1/;