sub _read_stdout {

    # Called when input is available for the output window.  Also checks
    # to see if the user has clicked Cancel.

    my($self) = @_;

    if ($self->{-finish}) {
	$self->kill_command;
    } else {
	my $h = $self->{-handle};
	if ( sysread $h, $_, 4096 ) {
	    my $t = $self->Subwidget('text');
	    $t->insert('end', $_);
	    $t->yview('end');
	} else {
	    $self->{-finish} = 1;
	}
    }
	
} # end _read_stdout