As documented in s/PATTERN/REPLACEMENT/msixpodualgcer in perlop:
Otherwise, if the PATTERN contains a $ that looks like a variable rather than an end-of-string test, the variable will be interpolated into the pattern at run-time.
...
e Evaluate the right side as an expression.
ee Evaluate the right side as a string then eval the result.
Essentially, with no switch, the variable is interpolated following qq rules. With one e, the value between the slashes is evaluated; all that lies between the slashes is the scalar, so it evaluates equivalently. With two es, the scalar is evaluated into the string value, and then that string value is passed through eval.

In reply to Re^3: Problem with Pattern matching and substitution using variables by kennethk
in thread Problem with Pattern matching and substitution using variables by shtihskar

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