Here's much the same thing, but using a closure. I'm sure this will slow down the process but can improve the usage of it by seperating the buffer from the rest of the code, and allowing easy reuse - and multiple buffers if desired - without needing to intersperse your code in amoungst other processing. It's a matter of tradeoffs, but I'm not sure on how much slower it will be.

my $buf = make_buf(3);
&$buf('hi');
&$buf('moo');
print join('  ', &$buf) . "\n"; # 'hi  moo'
$buf->('foo','no');
print join('  ', $buf->()) . "\n"; # 'moo  foo  no'

sub make_buf {
    my $size = shift || 3;
    my @buf;
    my $pos = -1;
    my $last = $size - 1;
    return sub {
        if (@_) {
            while (@_) { $buf[ $pos==$last ? $pos=0 : ++$pos ] = shift
+ }
        }
        elsif (wantarray) {
            return ($#buf==$last ? @buf[ $pos+1 .. $last, 0 .. $pos ] 
+: @buf);
        }
        else { warn "Call with an argument or in list context"; return
+; }
    }
}
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