You should always post a working snippet, or else say it is pseudocode. You have a couple of errors in the script, like Mainloop should be MainLoop. You should always use strict and warnings, which would have told you that.

Anyways, back to your real question... you need to pack your widgets and update your text widget with each print.

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

my $mw = MainWindow->new;
my $tw = $mw->Scrolled ("Text")->pack;

my $bu = $mw->Button(-text=>"Go",
         -command=>\&dosomething)->pack;

MainLoop;

exit;

sub dosomething {
for my $i (1 .. 500) {
   $tw->insert('end',"$i is $i\n" );
   $tw->update;
   $tw->see('end');
   select(undef,undef,undef,.1);
  };
}

__END__
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