open my $FILE, '<', "ESSID", or die "Can't open file: $!";

my @lines = <$FILE>;

my @Sel;
my $i = 0;
my @Selected;
my $checkButton;
foreach my $n ( @lines ) {

        chomp $n;

                $checkButton =  $mw->Checkbutton( -text => "$n",
                                                  -onvalue => 1,
                                                  -offvalue => 0,
                                                  -command => sub{push(@Sel, $n)} && sub{ $Selected[$i] = defined $Selected[$i] ? undef : $n;},
                                                  -variable => \$Selected[$i], )->pack(   -side => 'top',
                                                                                          -anchor => 'nw' );
        $i=$i+1;

}