You can look at the widget demo under "Canvas", and select "Simple 2D Plot", it has a button to print to printer. Copy the code. It goes something like this:

sub area_save {

    my($w, $pinfo) = @_;

    my($x1, $x2, $y1, $y2, $a);

    if($pinfo->{'areaX2'} != -1) {
    ($x1, $x2, $y1, $y2) =
      @$pinfo{'areaX1', 'areaX2', 'areaY1', 'areaY2'}; # slice !
    ($x1, $x2) = @$pinfo{'areaX2', 'areaX1'} if $x2 <= $x1;
    ($y1, $y2) = @$pinfo{'areaY2', 'areaY1'} if $y2 <= $y1;
    $a = $w->postscript('-x' => $x1, '-y' => $y1,
                -width => $x2 - $x1, -height => $y2 - $y1);
    } else {
    $a = $w->postscript;
    }

    $SIG{'PIPE'} = sub {};
    open(LPR, "| $pinfo->{'prcmd'}");
    print LPR $a;
    close(LPR);

} # end area_save
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