You should try

open STDIN, "<&", $c;
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If you don't have to use stdin only pass a filehandle, you can do this: Clear the FD_CLOEXEC flag like

fcntl $c, F_GETFD, 0; fcntl $c, F_SETFD, $x&~FD_CLOEXEC;
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Update: Does this post make sense? The whole point is, you should write open STDIN, "<&", $c; instead of *STDIN = $c; because the latter affects only perl's idea of stdin.

Excellent, thank you. Not only did this fix the problem, but it helped me expose a bug where I wasn't cleaning up my handles properly.

I had to use open(STDIN, '<&='.fileno($c)) because I am still in perl 5.6.1... sigh.

The sad thing is I was already using this method for STDOUT... don't know why I didn't use it for STDIN as well...

                - Ant
                - Some of my best work - (1 2 3)

Does this have advantages over the IO::Pipe method? (genuinly curious, not being difficult :)

It's been a good 10 years since I covered this in my OS classes and I haven't really had to use it since.

Yes, certainly.

If you copy the input from the stdin through a pipe, that's trivially less efficent than if you dupe the filehandle. In the second case, the new program just reads directly from whatever file stdin was connected to. With a pipe, you need a separate process that has to copy data from stdin to the pipe every time the second program needs data; under linux a pipe has a buffer of length 4096 by default, so the os has to do a task switch to the first process and back to the second one for every 4K bytes read (it is possible that some of the overhead can be avoided with the sendfile syscall). Also, the first process occupies memory and a process table entry. In addittion, you have to take care not to block data with too much buffering; also the pipe solution might not even work on win32.

Update: I actually spent some time and came up with a simple example.

use IO::Pipe;

$pipe = new IO::Pipe;

if($pid = fork()) {

    $pipe->writer();

    while(<STDIN>)
    {
        print $pipe $_;
    }
}
else
{

    $pipe->reader();

    while(<$pipe>)
    {
        $line = $_;

        print "CHILD: $line";
    }
}
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That's because $| affects only the currently select()ed output filehandle. IO::Pipe appears to subclass IO::Handle so you can just change

    $pipe->writer();
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to

    $pipe->writer();
    $pipe->autoflush();
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