perlcritic can identify a lexical variable which was declared with my, but was never set or used:

use strict;
use warnings;

my ($unused, $i, $j);
$i = $j; # uninitialized

__END__

"$unused" is declared but not used at line , column 1.
Unused variables clutter code and make it harder to read.  (Severity: 
+3)
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See also:

• Identify Unused and Uninitialised variables.