My question is: Why is the regexp compiler lenient enough to recognize $bar straight out as a variable reference, but one level removed (via $foo) and it will not operate?
This is a Good Thing from a security perspective.

Suppose you had a place for me to type a regex on a web form. So it shows up in a Perl variable, which you interpet dynamically as above. If I learn of that, I merely enter $foo[`evil command`] for my regex, and I've now haxored your system.

No, the present system must stay. It's the only way to ensure no "double-level" of interpretation, an absolute requirement for security.

-- Randal L. Schwartz, Perl hacker

In reply to Re: Regex Grumblings (Variable Interpolation) by merlyn
in thread Regex Grumblings (Variable Interpolation) by tadman

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