Can anyone explain why fileno in xfileno of the Open3.pm module returns undef in case if the following code is used, see below. This happens on Linux with perl 5.8.8 and Open3.pm 1.03. I also checked Open3.pm 1.09 and did not see any difference. I was not able to reproduce this with a own .pm file included. Background: I would like to write something that is able to launch a process in background (both Unix/Linux/Windows) and keep STDIN/STDOUT/STDERR connected AND allows to use select (on Windows, pipes cannot be used for select). 
use strict;
use IO::Socket;
use IPC::Open3;

my $childwriter;
my $childreader;
socketpair($childwriter, $childreader, AF_UNIX, SOCK_STREAM, PF_UNSPEC
+) ||  die "socketpair: $!";
my $stderrchildwriter;
my $stderrchildreader;
socketpair($stderrchildwriter, $stderrchildreader, AF_UNIX, SOCK_STREA
+M, PF_UNSPEC) ||  die "socketpair: $!";

my (@cmd) = "java -version 2>&1";
print "File handles:\n";
printf "out: $childwriter (%d), $childreader (%d)\n", fileno($childwri
+ter), fileno($childreader);
printf "err: $stderrchildwriter (%d), $stderrchildreader (%d)\n", file
+no($stderrchildwriter), fileno($stderrchildreader);
my $childpid = open3("<&$childreader", ">&$childreader", ">&$stderrchi
+ldreader", @cmd);

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BTW: IPC::Open3 does not take care for the fact that fileno(STDIN) == fileno(badhandle)also evaluates to true in case of fileno(STDIN) == 0 (which is often the case).

In reply to fileno unexpectly returns undef by kees

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