You should always use warnings; and use strict. Otherwise you will experience bugs. Anyways, you can store your default dir in the DATA section of your script, you can also use Inline::Files.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::JPEG;
use Tk::Dialog;

my $def_path;  #defaults to current dir in DATA

# read last stored value
while(<DATA>){
  if($_ =~ /^DIR:(.*)$/){ $def_path = $1 }
}

my $mw = MainWindow->new;

# make sure def_dir gets written when program closes
$SIG{INT} = sub { &close_it_up };
$mw->protocol('WM_DELETE_WINDOW' => sub {
                      &close_it_up
                   });


my $c = $mw->Canvas(
#                 -tile => $tile,
                 qw/-width 1500 -height 750/)->pack(-side => 'left');

my $path = $c->Label(-text => "Default Path For Saving Input Files",
          #-font => 'Arial 18 bold'
          )->place(-relx => 0.23, -rely => 0.4);

my $path_text = $c->Entry(-textvariable => \$def_path,
          -width => 50)->place(-relx => 0.4, -rely => 0.4);

my $path_button = $c->Button(-text => "Browse",
           #-font => 'Arial 8 bold',
           -width => 5,
           -command => [\&browse, $def_path])->place(-relx => 0.65, -r
+ely => 0.4);


MainLoop;

sub browse {
     my $init_dir = shift;

    $def_path = $mw->chooseDirectory(-title => 'Select directory',
                                               -initialdir => $init_di
+r,
                                               #-mustexist => 1 # scre
+ws up on linux
                                               );
    
}

sub close_it_up{

open(SELF,"+<$0")||die $!;
while(<SELF>){last if /^__DATA__/}
 truncate(SELF,tell SELF);

 $def_path ||='.';

 print SELF 'DIR:';
 print SELF "$def_path";
 print SELF $/;
   
 truncate(SELF,tell SELF);
 close SELF;

Tk::exit;
exit;
}

############################################################
__END__
__DATA__
DIR:'.'
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