I see the same as you in my local Perl (v5.20.3). Inspecting the layers shows that binmode adds to the defaults, rather than replacing them. You need to call if first with no layers in order to do a full reset. (Note: I've corrected the argument to encoding too)

#!/usr/bin/perl -w
            
use open qw/:std
            :encoding(iso-8859-1)/;       # default I/O encoding
            
my $s = "A \N{WHITE SMILING FACE} for you\n";

open (FILE, '> fpo');                     # in the actual code, may op
+en one of several things, or assign STDOUT to FILE
my @layers = PerlIO::get_layers(FILE);
print "Layers before binmode: @layers\n";
binmode(FILE, ':encoding(UTF-8)') if 1;    # override the default enco
+ding under certain conditions
@layers = PerlIO::get_layers(FILE);
print "Layers after binmode: @layers\n";
            
binmode(FILE) if 1;    # reset to raw
binmode(FILE, ':encoding(UTF-8)') if 1;    # add our new encoding
@layers = PerlIO::get_layers(FILE);
print "Layers after reset: @layers\n";
            
warn "About to print";                    # primitive trace statement
print FILE "$s";

[download]

And the output to terminal is

Layers before binmode: unix perlio encoding(iso-8859-1) utf8
Layers after binmode: unix perlio encoding(iso-8859-1) utf8 encoding(u
+tf-8-strict) utf8
Layers after reset: unix perlio encoding(utf-8-strict) utf8
About to print at /tmp/11119633.pl line 20.

[download]

There may be a neater way but this is at least a working solution, AFAICT.

In reply to Re: using binmode() to override default encoding specified in "use open" by hippo
in thread using binmode() to override default encoding specified in "use open" by raygun

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