The child process cannot access variables or call subroutines in your process. So your second criteria cannot be met. You will need to have the child write to a pipe from which you will read and write to the tied handle. 

use IPC::Open3 qw( open3 );

open(local *CHILD_STDIN, '<', '/dev/null')
   or die $!;

my $pid = open3(
   '<&CHILD_STDIN',
   '>&STDOUT',
   local *CHILD_STDERR,
   'ls file-that-does-not-exist.txt',
);

while (<CHILD_STDERR>) {
   print $tied_fh $_;
}

waitpid($pid, 0);

[download]
IPC::Open3 is quite low level. IPC::Run3 and/or IPC::Run can surely make this much simpler.

In reply to Re: Capturing STDERR (this is not a FAQ) by ikegami
in thread Capturing STDERR (this is not a FAQ) by mikosullivan

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