>perl -c -we"print $a"
Name "main::a" used only once: possible typo at -e line 1.

##</code><code>##

$Foo::Baar=1;
print "Foo::Bar is enabled" if $Foo::Bar;

##</code><code>##

my $foo = 42;
eval q[$foo++];

##</code><code>##

my($unused, $foo) = func();

##</code><code>##

{ open my $fh, ">$file" or die $! }  # touch

##</code><code>##

{
   my $lock = lock_something();  # lock released on scope exit
   do_stuff_that_needs_the_lock();
}

##</code><code>##

{
   my $tree = ...;
   my $sentry = Object::Destroyer->new( $tree, 'delete' );
   ...
}

##</code><code>##

my $object = bless \do {my $var} => $class;