use strict;
use warnings;
use diagnostics;

##</code><code>##

warn "$var\n";
print "@things\n";   # array with spaces between elements

##</code><code>##

chomp $var;
print ">>>$var<<<\n";

##</code><code>##

my $copy = $str;
$copy =~ s/([^\x20-\x7E])/sprintf '\x{%02x}', ord $1/eg;
print ":$copy:\n";

##</code><code>##

use Data::Dumper;
print Dumper(\%hash);
print Dumper($ref);

##</code><code>##

print ref $ref, "\n";

##</code><code>##

$ perl -MO=Deparse -p program.pl

##</code><code>##

open my $fh, '<', 'foo.txt' or die "can not open foo.txt: $!";

##</code><code>##

if (system $cmd) {
    print "Error: $? for command $cmd"
}
else {
    print "Command $cmd is OK"
}
$out = `$cmd`; print $? if $?;

##</code><code>##

eval { do_something() }; warn $@ if $@;

##</code><code>##

use Carp qw(cluck);
cluck("var is ($var)");

##</code><code>##

$ perl -MCarp::Always program.pl

##</code><code>##

# what the heck does /^\s+$/ mean?
use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new('/^\s+$/')->explain();

##</code><code>##

use WWW::Mechanize;
if ($mech->success()) { ... }