There's no way to define a sub to have the same syntax as print, much less a version with an extra handle.

It is possible to create a handle that writes to two other handles, though. See IO::Tee

how is the "die" function prototyped?

Use prototype to determine that.

$ perl -wle'print prototype("CORE::die")'
@
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But also see $SIG{__DIE__} in perlvar.

There's no way to define a sub to have the same syntax as print

I always thought function $foo $bar is another notation for $foo->function($bar) (which is also often used to imitate the new operator from other languages). So for example the following works:

use warnings;
use strict;

my $mp = MyPrint->new(*STDERR);

$mp->myprint("foobar\n");
myprint $mp "foobar\n";

package MyPrint;

sub new {
    my ($class, $out) = @_;
    return bless { out => $out }, $class;
}

sub myprint {
    my ($self, $text) = @_;
    my $out = $self->{out};
    print $out $text;
}
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I don't really know why STDERR->print "foobar" doesn't work though. It dies with

Can't locate object method "print" via package "IO::Handle"
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although the documentation says something else.

I always thought function $foo $bar is another notation for $foo->function($bar)

Ah yes. Indirect method call. It can cause headaches, so I don't use it. If a function or op with the same name as the method exists in the current namespace, it's not parsed as an indirect method call. Since print is an op, print $obj ... will never be an indirect method call, and it can't be used to solve the OP's problem.

$ perl -le 'use IO::Handle();STDOUT->print( qq{A "use IO::Handle" help
+s immensely} );' 
A "use IO::Handle" helps immensely
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The cake is a lie.
The cake is a lie.
The cake is a lie.

#!/usr/bin/perl
use strict;
use warnings;
use autodie;

sub mprint {
    my $message = shift @_; 
    my @files   = @_;
    for (@files) {
        print $_ "$message\n";
    }   
}

my $text = 'string of text';
open( my $out, ">",  "output.txt" );
open( my $log, ">>", "my.log" );

&mprint( $text, $out, $log );
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