$^X isn't properly converted to a shell literal. (i.e. Won't work if there's a space in $^X.) Fix: 
open3(
   undef,
   local *PIPE,
   undef,
   $^X, q!-le print 111;print STDERR 222!,
);

[download]

In reply to Re^3: IPC::Open3 misbehaving when STDOUT is not FD #1 by ikegami
in thread IPC::Open3 misbehaving when STDOUT is not FD #1 by sgifford

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