Mastering regular expressions is a perpetual goal, as just as you think you're on top of things, you discover something new. In the process of diagnosing a problem, I've encountered a behaviour that is a little peculiar. s/$bar/XYZ/g; Is not equivalent to: 
$foo = '$bar';
s/$foo/XYZ/g;

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As the former will substitite properly, and the latter will not. However, if you collar it, things will work out: 
$foo = '$bar';
s/\Q$foo\E/XYZ/g;

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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 seems like a double standard. The documentation I have read indicates that standard double-quote interpolation occurs, which would seem to suggest that $foo is interpolated into the string '$bar', and then processed accordingly.

In reply to Regex Grumblings (Variable Interpolation) by tadman

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