I wish to locate (...) variables that are never used.

Let Perl do this for you. Whenever possible, don't declare variables before you use them.

Bad:

my ($foo, $bar, $baz, $quux, $blah);
[download]

or

my $foo;
my $bar;
my $baz;
my $quux;
my $blah;
[download]

Good:

my $foo = /aoeu/ ? 15 : 16;

my $bar = Bar->new();

bless \my($baz), $class;

open my $quux, '<', $file or die $!;

my $bytes_read = read $quux, my($blah), $length;
[download]

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }