File handles opened using open FILE, ">", \$var don't have file descriptors since there are no corresponding OS file handles. Since open FILE2, ">&FILE" means open a new file from the file descriptor of "FILE", it's no suprise it doesn't work. The code below demonstrates this and a fix.

#!/usr/bin/perl -w

use strict;
use FileHandle;

printf("fileno(*STDOUT) = %d\n", fileno(*STDOUT));  # 1
printf("fileno(*STDERR) = %d\n", fileno(*STDERR));  # 2

open SAVED_STDOUT, ">&STDOUT" or die "couldn't save STDOUT: $!\n";
open SAVED_STDERR, ">&STDERR" or die "couldn't save STDERR: $!\n";

print SAVED_STDOUT "";  # to suppress warning about possible typo
print SAVED_STDERR "";  # to suppress warning about possible typo

my $captured_output = "";

close STDOUT;
open STDOUT, ">", \$captured_output
or die "couldn't re-open STDOUT: $!\n";

close STDERR;
#open STDERR, ">&STDOUT" or die "couldn't re-open STDERR: $!\n";
*STDERR = *STDOUT;

printf SAVED_STDOUT ("fileno(*STDOUT) = %d\n", fileno(*STDOUT));  # -1
printf SAVED_STDOUT ("fileno(*STDERR) = %d\n", fileno(*STDERR));  # -1

print "testing stdout capture 1\n";
print STDERR "testing stderr capture\n";
print "testing stdout capture 2\n";

close STDOUT; open STDOUT, ">&SAVED_STDOUT";
close STDERR; open STDERR, ">&SAVED_STDERR";

print $captured_output, "\n";
[download]

You could simplify the above code to:

#!/usr/bin/perl -w

use strict;

my $captured_output = "";

{
   local *STDOUT;
   open STDOUT, ">", \$captured_output
   or die "couldn't re-open STDOUT: $!\n";

   local *STDERR = *STDOUT;

   print "testing stdout capture 1\n";
   print STDERR "testing stderr capture\n";
   print "testing stdout capture 2\n";
}

print $captured_output, "\n";
[download]

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.