在Perl中使用Quotemeta？ 如何解决错误：“正则表达式中的嵌套量词； 标记为<— HERE”

Question

The following is the code:

my $vowels = "[aiou~NFKPQRIJ]";
my @diactok;
for $rx (@tokens) {
    $rx =~ s/.\K/$vowels?/g;
    if ($diac =~ /($rx)/) {
        push @diactok, $diac =~ /$rx/g;
    }
}

From this previous question: How do I tokenise a word given tokens that are subsumed incompletely in the word?

It's fine except for this error (I did "use diagnostics"):

Nested quantifiers in regex; marked by <-- HERE in m/(A[aiou~NFKPQRIJ]?l[aiou~NFKPQRIJ]?* <-- HERE [aiou~NFKPQRIJ]?y[aiou~N FKPQRIJ]?n[aiou~NFKPQRIJ]?)/ at tokenizeForCRFinput.pl line 47, line 28 8670 (#3) (F) You can't quantify a quantifier without intervening parentheses. So things like ** or +* or ?* are illegal. The <-- HERE shows in the regular expression about where the problem was discovered.

 Note that the minimal matching quantifiers, *?, +?, and ?? appear to be nested quantifiers, but aren't. See perlre. 

Uncaught exception from user code: Nested quantifiers in regex; marked by <-- HERE in m/(A[aiou~NFKPQRIJ]?l [aiou~NFKPQRIJ]?* <-- HERE [aiou~NFKPQRIJ]?y[aiou~NFKPQRIJ]?n[aiou~NFKPQRIJ]?)/ at tokenizeForCRFinput.pl line 47, line 288670. at tokenizeForCRFinput.pl line 47

Line 47 is this one:

if ($diac =~ /($rx)/)

I tried quotemeta but that didn't work - maybe I'm using it wrong? Some of the strings captured in $diac do indeed have special characters like '?' and '*' .

Answer 1

The line:

$rx =~ s/.\K/$vowels?/g;

Is the culprit, if you indeed have meta characters in @tokens . Try this:

$rx =~ s/(.)/ quotemeta($1) . "$vowels?" /eg;

Note that you cannot quotemeta the whole regex, since you have meta characters in $vowels that are needed.

Answer 2

The pattern is originally

(Al*yn)

You change it to

(A[aiou~NFKPQRIJ]?l[aiou~NFKPQRIJ]?*[aiou~NFKP...

Like the nessage says, [aiou~NFKPQRIJ]?* is wrong. You didn't specify what you want, so it's hard to give you a fix.

Maybe you want

(A(?:[aiou~NFKPQRIJ]?)l(?:[aiou~NFKPQRIJ]?)*(?:[aiou~NFKP...

If so, just use

$rx =~ s/.\K/(?:$vowels?)/g;

Maybe you want

(A(?:[aiou~NFKPQRIJ]?)(?:l[aiou~NFKPQRIJ]?)*(?:[aiou~NFKP...

If so, you'd need a much better regex parser than /./ .