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);