Declaring named capture groups

[elfring]

Named capture groups are supported for a while.
How do you think about a software extension for the possibility to declare the binding of regular expressions to identifiers before such identifiers would be reused at other places?

[zherczeg]

You can use (DEFINE) or (?:){0} blocks to define named blocks after a pattern, and you can append your "library" after a pattern with string concatenation.

[elfring]

I would appreciate improved descriptions for the mentioned functionality according to desirable pattern definitions.

[elfring]

• May patterns be declared or defined in multiple lines?
• Would any extra white-space characters influence subsequent pattern matching in undesirable ways?

[zherczeg]

With /x, (?x:), PCRE2_EXTENDED you can ignore spaces in the pattern, and even comments can be added. Inside (DEFINE), or (?:){0} everything is ignored. The only way to use something inside a (DEFINE) is recursion.

[PhilipHazel]

Take a look at the file testdata/testinput1 in the PCRE2 distribution. Search for the string "BNF". There you will find some complicated patterns that use (DEFINE) to transliterate BNF syntax descriptions more or less directly into named patterns groups.

[elfring]

Thanks for your link to another provided test case.

🔮 How will the chances evolve to improve the documentation any further also for this software area?

[elfring]

Would you like to avoid any typos at mentioned places?

Update candidates:

• https://github.com/PhilipHazel/pcre2/blob/8f3e11a355b2dfc362151bf2a2ba2ab21d6d58a4/doc/pcre2pattern.3#L2933
• https://github.com/PhilipHazel/pcre2/blob/8f3e11a355b2dfc362151bf2a2ba2ab21d6d58a4/doc/html/pcre2pattern.html#L2902

[PhilipHazel]

I have fixed that minor typo, thanks for noticing. I think this issue is now done.

[elfring]

💭 I would appreciate further documentation extensions for pattern definition groups.

[PhilipHazel]

PCRE2 documentation is not really the place for tutorials. For discussion of (?(DEFINE) see this web site:

https://www.regular-expressions.info/subroutine.html

[elfring]

PCRE2 documentation is not really the place for tutorials.

💭 I hope that this information source can become better and more complete (also in comparison to the other good information source which you mentioned).