To elaborate on what tye said:  due to the stringification problem, lexical file handles can't be used with the "<&" / ">&" feature.  Use "old-style" file handles instead: 

socketpair(STDERRCHILDWRITER, STDERRCHILDREADER, 
               AF_UNIX, SOCK_STREAM, PF_UNSPEC) ||  die "socketpair: $
+!";

[download]

and then specify them as ">&STDERRCHILDREADER", etc. to open3().

(Can't say, though, whether this will eventually help with your stated cross-platform goal — but it should at least get rid of the immediate problem...)

In reply to Re: fileno unexpectly returns undef by Eliya
in thread fileno unexpectly returns undef by kees

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