Re: alternation option end of string

Ray Andrews <[email protected]> writes:

> On 2026-05-02 15:25, Bart Schaefer wrote:
>> It wouldn't have worked even if you were using a regular 
>> expression,
>> for the same reason that (s|) didn't do what you want.  In the
>> comparison to the string "catszzz" the $ means the end of THAT 
>> string
>> (that is, after the third "z").  It does NOT mean the "end of
>> matching" up to that point.
> But I would have expected
> something like the $ usable as I'd intended.

These semantics for `$` in regexes goes back to the 60s; 
cf. e.g. the "Addressing by dollar sign" section on the ninth page 
of this PDF:

  https://github.com/arnoldrobbins/qed-archive/blob/master/sds-940/901112B_940_QED_RefMan_Jan69.pdf

There are different flavours of regex - POSIX BREs, POSIX EREs, 
PCREs, etc. - but i can't recall encountering a flavour where `$` 
doesn't have the semantics described by Bart. (i'd be interested 
to know if there is one.)


Alexis.