my $dir  = 'c:/';
my $from = '.pl';
my $to   = '.pl.bak';

while (<$dir*$from>) {
    my ($old,$new);
    $old = $new = $_;
    $new =~ s/$from$/$to/;
  next if $old eq $new;
    unless (exist($new)) {      
       rename $old, $new and 
       print "Renamed $old $new\n";
    }
}

sub exist {
    my $file = shift;
    if (-e $file) {
        print "File $file exists, owerwrite (y/n) ";
      return (<> =~ m/^y/i) ? 0 : 1
    }
  return 0;
}
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