Mini-Tutorial: Scoped changes to PerlIO layers

[ikegami]

If you want to temporarily change the PerlIO layers of a handle, your best bet might be to dup the handle.

use strict;
use warnings;

use PerlIO qw( );

sub dump_layers($*) {
    my ($prefix, $fh) = @_;
    my @layers = PerlIO::get_layers($fh);
    print($prefix, join(', ', @layers), "\n");
}

dump_layers('before: ', STDERR);

{
   open my $fh, '>&', STDERR or die $!;  # Dup the handle
   binmode $fh, ':encoding(UTF-8)';      # Do anything to the dup.
   dump_layers('local:  ', $fh);
}

dump_layers('after:  ', STDERR);         # The original is unaffected.

before: unix, perlio
local:  unix, perlio, encoding(utf-8-strict), utf8
after:  unix, perlio

The package variable itself could be replaced with the dup for the duration of the inner scope, but it shouldn't normally be needed.