$_来自这个Perl foreach循环？

sub _quote_search {
    my ( $self,@args ) = @_;
    my @ret;
    foreach my $v (@args) {
        if ( ref($v) eq "SCALAR" ) {
            push( @ret,$$v );
        }
        elsif ( exists $SEARCH_KEYS{ uc($_) } ) {
            push( @ret,$v );
        }
        elsif ( @args == 1 ) {
            push( @ret,$v );    # <3.17 compat: caller responsible for quoting
        }
        else {
            push( @ret,$self->Quote($v) );
        }
    }
    return @ret;
}