Is it possible to dup and add an encoding layer to a file handle? Here's what I'm trying: 
use strict;
use warnings;

my $x = "\x{42f}"."\n";

warn "printing to /tmp/foo\n";

open(my $fh, ">:utf8", "/tmp/foo") or die "open: $!";
print {$fh} $x;

warn "printing to STDOUT\n";

print $x;

warn "printing to duped STDOUT\n";

open(my $gh, ">&:utf8", \*STDOUT) or die "open: $!";
print {$gh} $x;

[download]
And here is the output under various run conditions (the Ҋ is a Cryillic capital "ya"): 
$ LANG=C ./script
printing to /tmp/foo
printing to STDOUT
Wide character in print at t5 line 13.
Ҋ
printing to duped STDOUT
Ҋ

$ LANG=en_US.UTF-8 ./script
printing to /tmp/foo
printing to STDOUT
Ҋ
printing to duped STDOUT
Ҋ

$ LANG=C ./script > /tmp/out
printing to /tmp/foo
printing to STDOUT
Wide character in print at t5 line 13.
printing to duped STDOUT
Wide character in print at t5 line 18.

$ LANG=en_US.UTF-8 ./script > /tmp/out
printing to /tmp/foo
printing to STDOUT
printing to duped STDOUT
Wide character in print at t5 line 18.

[download]
It seems that:
  1. The LANG setting affects the layers of STDOUT even if it is redirected to a file.
  2. My dup of STDOUT is not adding the utf8 layer
Is there a way I can dup a file handle and ensure that the utf8 I/O layer is present?

Btw, I'm using 5.8.0 - yes, very ancient.

In reply to dup and add an encoding layer to a file handle? by perl5ever

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