I ran into this problem the other day, and seek enlightenment: 
#!/usr/bin/perl -w

use strict;
use Tk;

my @SLIDERVALUES = (0, 0, 0, 0);
my @slider;

my $i;

sub show_array {
  print "\@SLIDERVALUES = ($SLIDERVALUES[0], $SLIDERVALUES[1], $SLIDER
+VALUES[2], $SLIDERVALUES[3])\n";
}

# window setup
my $mw = MainWindow->new;

foreach my $i (0 .. 3) {
  $slider[$i] = $mw->Scale
    (-from    => 30,
     -to    => 0,
     -orient    => 'vertical',
     -variable    => \$SLIDERVALUES[$i],
    )->pack
      (
      -side    => 'left',
      );
}

show_array();

# This breaks things!
@SLIDERVALUES = (5, 10, 15, 20);    

show_array();

$SLIDERVALUES[0] = 7;
$SLIDERVALUES[1] = 14;
$SLIDERVALUES[2] = 21;
$SLIDERVALUES[3] = 28;

show_array();

MainLoop;

[download]
When the line

    @SLIDERVALUES = (5, 10, 15, 20);

is commented out, the command line output is 

@SLIDERVALUES = (0, 0, 0, 0)
@SLIDERVALUES = (0, 0, 0, 0)
@SLIDERVALUES = (7, 14, 21, 28)

[download]
and the sliders take up position at 7, 14, 21, and 28, as expected.

If, however, that line is not commented out, we get 

@SLIDERVALUES = (0, 0, 0, 0)
@SLIDERVALUES = (5, 10, 15, 20)
@SLIDERVALUES = (7, 14, 21, 28)

[download]
at the command line, and the sliders all stay at 0.

I'd like to understand how the -variable option is being ignored, and I'd also like tips on how I could have further diagnosed this problem.

Many thanks...

In reply to Perl/Tk and the "-variable => \$var" option by Mikster

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