Here is a script that saves, redirects, and restores STDOUT and STDERR using various methods: 
        #!/usr/bin/perl
        open my $oldout, ">&STDOUT"     or die "Can't dup STDOUT: $!";
        open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";
    
        open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!"
+;
        open STDERR, ">&STDOUT"     or die "Can't dup STDOUT: $!";
    
        select STDERR; $| = 1;      # make unbuffered
        select STDOUT; $| = 1;      # make unbuffered
    
        print STDOUT "stdout 1\n";  # this works for
        print STDERR "stderr 1\n";  # subprocesses too
    
        open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
        open STDERR, ">&OLDERR"    or die "Can't dup OLDERR: $!";
    
        print STDOUT "stdout 2\n";
        print STDERR "stderr 2\n";

[download]
It would be straightforward to then slurp in the contents of the saved-off files. Or did I misunderstand the question?

In reply to Re^3: Capturing STDERR using IO::Handle by educated_foo
in thread Capturing STDERR using IO::Handle by rvosa

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.