file1
file2
file3

##</code><code>##

file1 new-file-1
file2 new-file-2
file3 new-file-3

##</code><code>##

while (<>) {
  chomp;
  ... derive $new from $_ ...
  print $_, ' --> ', $new, "\n"; # use ' --> ' as the delimiter
}

##</code><code>##

while (<>) {
  chomp;
  my ($old, $new) = split(' --> ', $_, 2);
  unless (rename $old, $new) {
    warn "unable to rename $old to $new: $!\n";
  }
}