Assuming correctness of the premise that these are interview questions, helping people advance beyond their skills is detrimental to everyone but the applicant.

• Applicants are hired under false pretenses.
• Employers receive less for their money.
• Employees must deal with new hires who don't really know Perl, and the code that they produce.
• The job market for competent Perl programmers is reduced.
• The code these applicants produce supports the idea that Perl is a write-once, read-never language, and the department should move to Java.

That said, it's really up to the individual to decide whether to help someone pass a job interview. In many cases, it's probably impossible to determine the nature of a question without being a right bastard about it. YMMV, etc.