my $DoButton = 
        $mode_buttons->Button(
            -text => 'Continue',
            -command => sub {&do_setup()}
            )->pack (-side => 'left', -expand => 1);

##</code><code>##

    my $DoButton =
        $mode_buttons->Button(
            -text => 'Continue',
            -command => \&do_setup   ### provide a code_ref, not anon_sub
          )->pack (-side => 'left', -expand => 1);

##</code><code>##

     ... -command => sub {&getTool();&CleanUp();},

##</code><code>##

     ... -command => sub {getTool();CleanUp();},   ### drop the "&"

##</code><code>##

    ... -command => [ \&func_name, $arg1, $arg2 ],