sub shell_quote {
    my ($rerr, $s) = _shell_quote_backend @_;
 
    if (@$rerr) {
        my %seen;
        @$rerr = grep { !$seen{$_}++ } @$rerr;
        my $s = join '', map { "shell_quote(): $_\n" } @$rerr;
        chomp $s;
        croak $s;
    }
    return $s;
}