Re: Question about regex with negated character class

On 2022-04-25, Roger L Costello <costello@mitre.org> wrote:
> Hi Folks,
>
> On page 12 of the Flex specification it says this:
>
> "A negated character class such as [^A-Z] will match a newline
> unless \n (or an equivalent escape sequence) is one of the characters
> explicitly present
> in the negated character class (e.g., [^A-Z\n]). This is unlike how many other
> regular expression tools treat negated character classes ..."


I suspect this is a documentation mistake (in terms of the the remark it
makes about other regex implementations).


There is something special in Flex with regard to newlines: namely the
any-character regular expression . (dot) does not match any character:
it excludes the newline. The documenter might have momentarily gotten
their wires crossed, misremembering what is the special behavior.


Or else, I also agree with John that it may in fact be a remark about
regex implementations in line-oriented text processing utilities, which
(in their standrad forms, e.g. POSIX) don't have multi-line matching
features in which \n appears as a character.


--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

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