Re: Case-insensitive regular expressions

[Shawn Wagner]

4. Adopt the vim convention that \c anywhere in a regex makes it
case-insensitive.  Clean and fully isolated from the rest.

Going that route, I'd rather lift a page from perl & co and indicate it by
looking for (?i) at the very beginning of a regular expression, and then
just skipping over those characters when passing the RE to regcomp().

Looking through the GNU ed source, that might be the easiest approach.
Checking for a flag after the RE before it's compiled is looking a bit
complicated to add.


On Tue, Jul 6, 2021 at 4:12 PM John Cowan <cowan@ccil.org> wrote:

>
>
> On Tue, Jul 6, 2021 at 4:38 PM Shawn Wagner <shawnw.mobile@gmail.com>
> wrote:
>
> 1. A command line switch to match all REs that way. Easiest to add, but
>> then what if you want some patterns to be sensitive and some not in the
>> same session? It's just the reverse of the current form.
>>
>
> I think that would be Very Bad.
>
>> 2. Adding an I flag to REs in address ranges, s, g, etc. (I instead of i
>> to
>> match GNU sed and for the same reason - to avoid ambiguity with the
>> existing i command).
>>
>
> A possibility.
>
>> 3. Take a page from GNU grep and add support for using PCRE2 regular
>> expression engine via ed -P,
>>
>
> Certainly provides the most function, but may end up with an editor whose
> regex package is larger than the rest of it!
>
> 4. Adopt the vim convention that \c anywhere in a regex makes it
> case-insensitive.  Clean and fully isolated from the rest.
>
> Implementation notes:  (a) You need to foldcase both the regex (before it
> is compiled) and the text being matched; (b) Unicode case folding has a
> bunch of special cases.
>
>
>
>