I think you are going to run into problems with this type of script, where you combine Tk and GD.

From the Perldoc for GD::Graph

BUGS
GD::Graph objects cannot be reused. To create a new plot, you have to 
+create a new GD::Graph object.
[download]

What that means, is that everytime you update your graph, you will get a memory increase. If it is a long running program, it will become unacceptable.

For something simple like a bar graph, you would be better of making a Tk Canvas, and creating rectangles to show your bars. It won't leak memory when you update, and you would be able to add more color to the bars. Additionally, it will use less memory than a script that uses GD.

In this example, I have it upside down. You can add axis and text if you want. It is also just a "quick demo", and the design can be improved upon.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use MeM;

my $w=20;
my $x=0;
my $y=0;

my %colors = (
   0 => ['black','yellow'],
   1 => ['yellow','black'],
   2 => ['white','green'],
   3 => ['green','white'],
   4 => ['grey','red'],
   5 => ['red','grey'],
   6 => ['blue','white'],
   7 => ['white','blue'],
   8 => ['orange','grey45'],
   9 => ['grey45','orange'],
);

my %bardata = (
   0 => rand 200,
   1 => rand 200,
   2 => rand 200,
   3 => rand 200,
   4 => rand 200,
   5 => rand 200,
   6 => rand 200,
   7 => rand 200,
   8 => rand 200,
   9 => rand 200,
);

my %bars;

my $mw=tkinit;
my $c = $mw->Canvas->pack;

for (0..9) {
  $bars{$_} = $c->createRectangle($x,$y,$x+20,$bardata{$_},
             -fill=> ${$colors{$_}}[0],
          );

my $text = $c->createText($x+10,$y+10,
           -anchor=>'center',
           -fill => ${$colors{$_}}[1],
           -text => $_
          );

      $x+=20;
}

$mw->Button(
    -text    => "Save",
    -command => [sub {
         $c->update;
         my @capture=();
         my ($x0,$y0,$x1,$y1)=$c->bbox('all');
         @capture=('-x'=>$x0,'-y'=>$y0,-height=>$y1-$y0,-width=>$x1-$x
+0);
         $c -> postscript(-colormode=>'color',
                               -file=>$0.'.ps',
                               -rotate=>90,
                               -width=>800,
                               -height=>500,
                               @capture);

                              }

  ]  )->pack;

$mw->repeat(2000, sub{ &update });

MainLoop;
########################################################## 
sub update{

$x=0;
$y=0;

 %bardata = (
   0 => rand 200,
   1 => rand 200,
   2 => rand 200,
   3 => rand 200,
   4 => rand 200,
   5 => rand 200,
   6 => rand 200,
   7 => rand 200,
   8 => rand 200,
   9 => rand 200,
);
for (0..9) {

  $c->delete( $bars{$_}  );

  $bars{$_} = $c->createRectangle($x,$y,$x+20,$bardata{$_},
             -fill=> ${$colors{$_}}[0],
          );

  my $text = $c->createText($x+10,$y+10,
           -anchor=>'center',
           -fill => ${$colors{$_}}[1],
           -text => $_
          );

      $x+=20;
}

}
[download]

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