Re: Various forms of Regexps in tools (standard and non-standard) (was Re: CLARIFICATION ...)

On Fri, 5 Jul 2024 04:00:01 +0200, Janis Papanagnou wrote:

On 05.07.2024 03:05, Lawrence D'Oliveiro wrote:
>

The Perl style seems to have become something of a de-facto standard.

 
Hardly. First, there's differences on the functional level; Perl
supports with their regexp library functions that are not part of the
Regular Expression grammar class, they exceed that class. The
consequence is that for that subset there's no O(N) (linear) complexity
guaranteed any more.

Precisely. Many users of REs seem to feel it is useful to at least
have the option of such extensions, and they are willing to pay that
price.

Second, there's syntactical differences between tools, that are
necessary to handle meta-characters in their specific language
context; in one tool meta-characters need, e.g., to be escaped where
in another context that's not necessary. How can something be a
standard when (standard-)tools do not support that.

Surely they do it the way that Perl does. Hence “Perl style”.

Moreover, when speaking about [de facto] "standards"; what would
that mean in the light of existing (real) standards ...

It means there is a standard library (actually a whole bunch of them)
you can link against to immediately support that style of regular
expression.

<https://packages.debian.org/search?keywords=pcre&searchon=names&suite=stable&section=all>