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POHow do I make an arbitrary Perl regex wholly non-capturing? (Answer: You Can't)
 

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  1. POHow do I make an arbitrary Perl regex wholly non-capturing? (Answer: You Can't)
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    <p>How can I remove capturing from arbitrarily nested sub-groups in a a Perl regex string? I'd like to nest any regex into an enveloping expression that captures the sub-regex as a whole entity as well as statically known subsequent groups. Do I need to transform the regex string manually into using all non-capturing <code>(?:)</code> groups (and hope I don't mess up), or is there a Perl regex or library mechanism that provides this?</p> <pre><code># How do I 'flatten' $regex to protect $2 and $3? # Searching 'ABCfooDE' for 'foo' OK, but '((B|(C))fo(o)?(?:D|d)?)', etc., breaks. # I.E., how would I turn it effectively into '(?:(?:B|(?:C))fo(?:o)?(?:D|d)?)'? sub check { my($line, $regex) = @_; if ($line =~ /(^.*)($regex)(.*$)/) { print "&lt;", $1, "&gt;&lt;", $2, "&gt;&lt;", $3, "&gt;\n"; } } </code></pre> <p><strong>Addendum:</strong> I am vaguely aware of <code>$&amp;</code>, <code>$&#96;</code>, and <code>$'</code> and have been advised to avoid them if possible, and I don't have access to <code>${^PREMATCH}</code>, <code>${^MATCH}</code> and <code>${^POSTMATCH}</code> in my Perl 5.8 environment. The example above can be partitioned into 2/3 chunks using methods like these, and more complex real cases could manually iterate this, but I think I'd like a general solution if possible.</p> <p><strong>Accepted Answer:</strong> What I wish existed and surprisingly (to me at least) does not, is an encapsulating group that makes its contents opaque, such that subsequent positional backreferences see the contents as a single entity and names references are de-scoped. <a href="https://stackoverflow.com/questions/3552850/how-do-i-make-an-arbitrary-perl-regex-wholly-non-capturing-answer-you-cant/3553154#3553154"><strong>gbacon</strong></a> has a potentially useful workaround for Perl 5.10+, and <a href="https://stackoverflow.com/questions/3552850/how-do-i-make-an-arbitrary-perl-regex-wholly-non-capturing-answer-you-cant/3552965#3552965"><strong>FM</strong></a> shows a manual iterative mechanism for any version that can accomplish the same effect in specific cases, but <a href="https://stackoverflow.com/questions/3552850/how-do-i-make-an-arbitrary-perl-regex-wholly-non-capturing-answer-you-cant/3553154#3553154"><strong>j_random_hacker</strong></a> calls it that there is no real language mechanism to encapsulate subexpressions.</p>
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    1. CO+1 Nice job with the follow-up edits.
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