open(OUTPUT,">>${len}.words");
while(<>){
  chomp($_);
  $len = length($_);
  print OUTPUT "$_\n";
}
close(OUTPUT);
[download]

This doesn't do what the others do. For one, $len isn't defined before the open. Secondly, you don't have an outer loop involved to be able to re-open the files as needed.

Secondly, if you're going to use $_, then use it. Don't piddle around. If you're going to use a named variable (and I'm not saying this is bad), then name it. Otherwise, take advantage of Perl-isms.

while (<>) {
    chomp;
    my $len = length;
    print OUTPUT $_, $/;
}
[download]

It wouldn't be nice unless I posted my own (unBenchmarked) version.

use IO::File;
my %Handles;
while (<>) {
    my $handle = $Handles{length} ||= IO::File->new(">" . length - 1);
    print $handle $_;
}
# This is unnecessary unless you're anal (like I try to be)
$_->close for values %Handles;
[download]

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