How do I use a variable as a regex modifier in Perl?

Question

I\'m writing an abstraction function that will ask the user a given question and validate the answer based on a given regular expression. The question is repeated until the

Answer 1

Upshot: is there a way to dynamically specify a regular expression's modifiers?

From perldoc perlre:

"(?adlupimsx-imsx)" "(?^alupimsx)" One or more embedded pattern-match modifiers, to be turned on (or turned off, if preceded by "-") for the remainder of the pattern or the remainder of the enclosing pattern group (if any).

This is particularly useful for dynamic patterns, such as those read in from a configuration file, taken from an argument, or specified in a table somewhere. Consider the case where some patterns want to be case-sensitive and some do not: The case-insensitive ones merely need to include "(?i)" at the front of the pattern.

Which gives you something along the lines of

$isValid = $ans =~ m/(?$modifier)$validationRe/;

Just be sure to take the appropriate security precautions when accepting user input in this way.