It's very simple, once you've seen the trick. You will see this type of callback in all sorts of Tk code.

foreach my $button ( @buttons ) {
   .........
   ........
   
    # Add a button widget
    $frame->Button(
        -anchor  => 'nw',
        -text    => "change " . $button,
        -command => [\&print_button_label, $button],
    )->pack( -side => 'left', -anchor => 'w', -padx => 2 );
}

###############################################
sub print_button_label{
    my $button = shift;
    print "button\n";
}
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There are a few variations on the callback syntax. You could also do

-command => sub { print_button_label( $button ) },
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You could also use the 'current' tag trick, where you bind a <1> press to a sub which gets the currently active widget, then use cget on the widget, to find it's name or other property; but you will usually see it as I shown above.