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To not capture recursive group while collecting certain matches

by Anonymous Monk
on Nov 29, 2021 at 09:55 UTC ( #11139211=perlquestion: print w/replies, xml ) Need Help??

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

How regex match must not capture recursive group used and required inside when collecting all the matched captured groups?
just illustration
@m='lkjkljkjlkhkjkfjkfkvklkv'=~/^\w*(kl(?1)\w*).*?(kv)/g;
How to manage m contains all matched kv correctly clean from matched recursive ?

Replies are listed 'Best First'.
Re: To not capture recursive group while collecting certain matches
by Anonymous Monk on Nov 29, 2021 at 16:31 UTC

    As given, your example does not match anything. If you use re 'debug'; you will get a fairly cryptic trace of what the regular expression is doing:

    $ perl -Mre=debug -E 'my @m='lkjkljkjlkhkjkfjkfkvklkv'=~/^\w*(kl(?1)\w*).*?(kv)/g; say for @m;'
    Compiling REx "^\w*(kl(?1)\w*).*?(kv)"
    Final program:
       1: SBOL /^/ (2)
       2: STAR (4)
       3:   POSIXU\w (0)
       4: OPEN1 (6)
       6:   EXACT <kl> (8)
       8:   GOSUB1-4:4 (11)
      11:   STAR (13)
      12:     POSIXU\w (0)
      13: CLOSE1 (15)
      15: MINMOD (16)
      16: STAR (18)
      17:   REG_ANY (0)
      18: OPEN2 (20)
      20:   EXACT <kv> (22)
      22: CLOSE2 (24)
      24: END (0)
    floating "klkl" at 0..9223372036854775807 (checking floating) anchored(SBOL) minlen 6 
    Matching REx "^\w*(kl(?1)\w*).*?(kv)" against "lkjkljkjlkhkjkfjkfkvklkv"
    Intuit: trying to determine minimum start position...
      doing 'check' fbm scan, 0..22 gave -1
      Did not find floating substr "klkl"...
    Match rejected by optimizer
    Freeing REx: "^\w*(kl(?1)\w*).*?(kv)"
    

    The trace says your match never got started because the string being matched does not contain 'klkl'. The first 'kl' is the literal one from your regular expression; the second is because of the recursion. I believe that even if the string contained 'klkl' there would be no match, because there is no way for the recursion to end; it would just look for 'klklkl', then 'klklklkl', and so on.

    Can you say what you expect @m to contain in your example?

    And can you provide an example where you match against the shortest possible string that you want to match successfully?

Re: To not capture recursive group while collecting certain matches
by LanX (Sage) on Nov 29, 2021 at 17:15 UTC
    > clean from matched recursive ?

    There are no "recursive" inner matches returned.

    It's unclear what you want but the following demonstrates how to match only at the top level of a recursive match.

    DB<173> x 'bla[[abc]]foo' =~ / ( \[ (?1)* \w* \] ) /xg; 0 '[[abc]]'

    Not what you wanted?

    Then see how (not) to ask a question

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery

Re: To not capture recursive group while collecting certain matches
by LanX (Sage) on Nov 29, 2021 at 10:40 UTC
Re: To not capture recursive group while collecting certain matches
by Anonymous Monk on Nov 29, 2021 at 10:39 UTC
    Use named patterns?

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