Phil

sub _print {
  my ($msg) = @_;

  print $msg, "\n";
  print LOG $msg, "\n";
}

_print("hello");
_print("world");
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Why not

sub _print {
  print $msg, @_;
  print LOG $msg, @_;
}

_print("hello");
_print("world");
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That way, you can print lists, and $, and $\ will be obeyed. OTOH, the simplest solution is probably the following:

use IO::Tee ();

my $fh_out = IO::Tee->new(\*STDOUT, \*LOG);
select($fh_out);

print("hello");
print("world");
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But there are problems with using select.

if (!(my $pid = open(STDOUT, "|-"))) {
    die "fork failed: $!" unless defined $pid;
    while (<STDIN>) {
        print $_;
        print LOG $_;
    }
    exit;
}
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