This is what I used for URLs in PM::CB::GUI:

sub browse {
    my ($url) = @_;
    my $action = {
        MSWin32 => sub { system 1, qq{start "$url" /b "$url"} },
        darwin  => sub { system qq{open "$url" &} },
    }->{$^O}    || sub { system qq{xdg-open "$url" &} };
    $action->();
}
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