open the read file <
open the write file if necessary > or >>
print WRITEFILE "data ...\n";
If a module will handle many events install it. Problem is in the module installation. There are a lot of cases where users do not have access to root and use of the CPAN shell.
Considering your prior attempt at using sed for this, I am assuming this is for local use of some sort.
WWW::Mechanize is an interesting module.