Two neat concepts I noticed in perlsub and perlref in February, 2007:

# Try and catch using prototypes. (Almost verbatim from perlsub.)

sub try (&$) {
    my ($try, $catch) = @_;

    eval { &$try; };
    if ($@) {
        local $_ = $@;
        &$catch;
    }
}

sub catch (&) {
    $_[0]
}

try { 
    die "phooey";
} catch {
    /phooey/ and print "unphooey\n";
};
[download]

# Nested subroutines.

sub frobnicate {
   my $input = shift;

   local *grok = sub {
      my $input = shift; 
      # grok's $input is lexical, and therefore
      # different from the outer $input.

      return $input . " grokked!";
   }; # Note the semicolon.

   return grok($input);
}

print frobnicate('foo'), "\n";

# However, this will work as well.
sub frobnicate_again {
    my $input = shift;

    local *grok = sub { return $input . " grokked!"; };

    return grok($input);
}

print frobnicate_again('foo'), "\n";
[download]

I always wondered how to do the latter in Perl.

A feature not known to me, learned while reading Programming Perl (3rd ed.):

my $ip = 127.0.0.1;
printf "%vd\n", $ip;
[download]