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file1
file2
file3

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

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

while (<>) {
  chomp;
...
    warn "unable to rename $old to $new: $!\n";
  }
}