use 5.010;
use strict;
use warnings;

my $x = 23;
my $y;

debug("x='$x' y='$y'");
debug(sprintf "x='%s' y='%s'", ($x // ''), ($y // ''));

sub debug {
    say shift

}

##</code><code>##

use 5.010;
use strict;
use warnings; 

my $x = 23;
my $y;

debug({x => $x, y => $y});

sub debug {
    my ($d) = @_;
    my $s = join ' ', map { sprintf("$_='%s'", ($d->{$_} // '')) } sort keys %$d;
    say $s;
}

##</code><code>##

use 5.010;
use strict;
use warnings; 

my $x = 23;
my $y;

debug("x='%s' y='%s'", $x, $y);

sub debug {
    my ($fmt, @params) = @_;
    printf "$fmt\n", map { $_ // '' } @params;
}