Hi tamaguchi,

If by width of the screen you mean just the window itself, that's easy:

$c->pack(-expand => 1, -fill => 'both');
[download]

But if you mean, as I think you do, the width of the monitor screen, try using the methods vrootheight and vrootwidth as well:

#!/usr/bin/perl -w

use Tk;
use strict;    

my $mw = MainWindow->new;
my $vh = $mw->vrootheight;
my $vw = $mw->vrootwidth;

# Note that the 'virtual window' height and width are $vh and $vw
# respectively, so we use those dimensions for our Canvas height 
# and width, and let the Canvas expand and fill in both x and y
# directions.
#
my $c = $mw->Canvas(
-width => $vw, 
-height => $vh, 
-background =>'blue', 
-scrollregion =>[0, 0, 100, 100]); 
$c->pack(-expand => 1, -fill => 'both');

$c->createRectangle(100, 100, 150, 150, -fill => 'yellow'); 

MainLoop;
[download]

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