Sounds like you want ambrus's 3rd solution

# Open log file once
open(MYFILE, '>>', $qfn)
    or die("Cannot open file $qfn for appending: $!\n");

...

print_to($to_file ? *MYFILE : *STDOUT, $str);
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Better yet, use a lexical

open(my $MYFILE, '>>', $qfn)
    or die("Cannot open file $qfn for appending: $!\n");

...

print_to($to_file ? $MYFILE : *STDOUT, $str);
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Finally, if you want to reopen the file every time you call print_to,

my $MYFILE;
if ($to_file) {
    open($MYFILE, '>>', $qfn)
        or die("Cannot open file $qfn for appending: $!\n");

    print_to($to_file ? $MYFILE : *STDOUT, $str);
} else {
    $MYFILE = *STDOUT;
}

print_to($MYFILE, $str);
[download]