First, you are reinventing the wheel: see uniq in List::MoreUtils and How do I compute the difference of two arrays? How do I compute the intersection of two arrays? in perlfaq4. But this, of course, does not answer your question.

keys returns a list, not an array, and so if you want to return an array reference you necessarily need to create a new array. You could reduce your character and line count by simply returning an anonymous array reference: 

sub unique {
  my @refs = @_;
  my %files = ();
  foreach my $ref (@refs) {
    $files{$_}++ foreach (@$ref);
  }
  return [keys %files];
}

[download]

For more info, see Making References in perlref.

In reply to Re: Return reference to hash keys by kennethk
in thread Return reference to hash keys by miketosh

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.