After some debugging, I found that open3 defaults to using the same pipe for the child's STDOUT and STDERR.
Yes. It's easy to skip over that fact, but it is in the documentation: 
       Extremely similar to open2(), open3() spawns the given $cmd and con-
       nects RDRFH for reading, WTRFH for writing, and ERRFH for errors.  If
       ERRFH is false, or the same file descriptor as RDRFH, then STDOUT and
       STDERR of the child are on the same filehandle.
So the only filehandle that needs to be directly set is ERRFH. You can leave the other two alone.
(WTF?!? I'd use open2 if I wanted to do that.)
Not in the same way. You might use a shell to redirect STDERR to STDOUT and then read that new (combined) stream with open2, but you cannot use open2 to read STDERR directly. That's a different behavior from open3 making both streams available on the same perl filehandle (without needing an intervening shell for the redirection).
--
Darren

In reply to Re^2: open3 and IO::Select by ddunham
in thread open3 and IO::Select by stephens2k

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.