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

You need to use the eval function. The below code will work:

sub ask {
    my ($prompt, $validationRe, $caseSensitive) = @_;
    my $modifier = ($caseSensitive) ? "" : "i";
    my $ans;
    my $isValid;

    do {
        print $prompt;
        $ans = <>;
        chomp($ans);

        # What I want to do that doesn't work:
        # $isValid = $ans =~ /$validationRe/$modifier;

        $isValid = eval "$ans =~ /$validationRe/$modifier";

        # What I have to do:
        #$isValid = ($caseSensitive) ?
        #    ($ans =~ /$validationRe/) :
        #    ($ans =~ /$validationRe/i);

    } while (!$isValid);

    return $ans;
}