From the perl/Tk FAQ:

11.7. How do I get a Canvas to output PostScript(c)? 
 
 Many thanks to Tom Oelke <tpo9617@rit.edu> for providing this questio
+n,
 answer & snippet of code: 
 
  The following section of code gets the postscript code for the secti
+on of
  canvas that's top-left corner is at $min_x, $min_y, and has a width 
+and
  height equivalent to the displayed region. This ps code is then pipe
+d out
  to lpr to be printed. 
 
     my $ps = $canvas->postscript( '-x' => $min_x,
                                   '-y' => $min_y,
                                   -width => $canv->Width,
                                  -height => $canv->Height);
     open (PS, "| lpr"); # customize with -Pname e.g. 
     print PS $ps;
     close (PS);
 
 Whereas you would use something like: 
 
     open (PS, ">file.ps"); # to output to a file
     print PS $ps;
     close (PS);
[download]

Update: A better explanation: the first bit of code sends the canvas data in postscript form to a (unix) printer lpr. The second bit of code creates a postscript file that you can send to the printer directly via

% lpr file.ps
[download]

or you can open it with ghostscript to print it on a non-postscript printer.