Why does open with :w and :append still overwrite the file?

Question

I got the following code to try out file opening and writing (without spurt):

sub MAIN {
    my $h = open 'somefile.txt', :w, :a;

    for 1..4 {
        $fh.put: "hello";
    }
    $fh.close;
}

What I expected is that with each run, it should append 4 additional lines with "hello" to the file. However it still seems to overwrite the file, after 2 or more runs there are still only 4 lines.

$ perl6 opening.p6
$ cat somefile.txt
hello
hello
hello
hello
$ perl6 opening.p6
$ cat somefile.txt
hello
hello
hello
hello

Adding or removing :a or :append doesn't seem to influence this behaviour, what am I missing?

Answer 1

According to the open documentation, you want

my $h = open 'somefile.txt', :a;

The one and two-letter shorthands are not modifiers, but useable in isolation, with :w expanding to

:mode<wo>, :create, :truncate

and :a expanding to

:mode<wo>, :create, :append

mimicking POSIX.

The combination :w, :append you tried should in fact also open the file in append mode - but only after truncating it first, which doesn't seem particularly useful...