regex - 如何在Perl中将变量用作正则表达式修饰符？

Question

我正在编写一个抽象函数，该函数将向用户提出一个给定的问题，并根据给定的正则表达式验证答案。重复该问题，直到答案与验证正则表达式匹配为止。

但是，我也希望客户端能够指定答案是否必须区分大小写。

所以像这样:

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;

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

    } while (!$isValid);

    return $ans;
}

结果:有没有一种方法可以动态指定正则表达式的修饰符？

Answer 1

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

从 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.

这给你一些类似的东西

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

以这种方式接受用户输入时，只需确保采取适当的安全预防措施即可。