Re^3: Help combining two regex's into one

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Re^4: Help combining two regex's into one by AnomalousMonk (Archbishop) on Jan 16, 2013 at 04:19 UTC
From perlre, identical in both Strawberry 5.14.2.1 local docs and 5.16.2 on-line docs (emphases added): \K [6] Keep the stuff left of the \K, don't include* it in $&* (Note [6] simply refers to the discussion in the "Look-Around Assertions" section.) From "Look-Around Assertions": There is a special form of this construct, called "\K", which causes the regex engine to "keep" everything it had matched prior to the "\K" and not include* it in $&.* Hmmm... I suppose when I read these sections heretofore, my attention was drawn to the "don't include..." clauses and I more or less ignored the "left of" and "prior to" statements. My naive association of "keep" is with inclusion: in this specific instance, everything to the right of `\K` is (or could be) included in `$&`. The docs seem to be using "keep" in the sense of "keep back", i.e., "to exclude": everything to the left of `\K` is "kept back" from inclusion in `$&`. Perhaps they are discussing the behavior `\K` in the context of substitution: everything left of the `\K` is not included in `$&` and so cannot be zapped by substitution: it is "kept safe" from substitution. But `\K` is equally valid and useful in both `m//` matching and `s///` substitution, so... I can't say I would agree with the perhaps subtle interpretation given to "keep" in the documentation, but it is fully clarified by the "don't include" language and by the examples, so I doubt this qualifies as a doc-bug. Update: LanX: Almost as confusing like using single line and multi line modifier at the same time... ++That!	[reply] [d/l] [select]
Re^5: Help combining two regex's into one by Kenosis (Priest) on Jan 16, 2013 at 04:38 UTC
...everything left of the \K is not included in $& and so cannot be zapped by substitution: it is "kept safe" from substitution. Well said... Given this, I might read perlre as "Keep the stuff left of the \K, i.e., don't include it in $&". Put another way, if the stuff left of \K were included in $&, it wouldn't be kept--and I believe this is the essence of your quote above. Got a great laugh from your Update! Thanks for that...	[reply]
Re^4: Help combining two regex's into one by LanX (Saint) on Jan 16, 2013 at 03:11 UTC
Just a matter of perspective: the left part which is kept unchanged is the one ignored from substitution, because the right part is kept in '$&'. So both parts are kept, just in different aspects. Almost as confusing as using single line and multi line modifiers at the same time...	[reply]