Re: [PATCH] [[:blank:]] only matches on SPC and TAB

[Stephane Chazelas <stephane.chazelas@gmail.com>]

2018-05-14 04:27:46 +0200, Sebastian Gniazdowski:
> On 13 May 2018 at 23:25, Stephane Chazelas <stephane.chazelas@gmail.com>
> wrote:
> 
> > I noticed that [[:blank:]] was not matching on non-ASCII blank
> > characters. In a typical UTF-8 GNU locale, [[:blank:]] normally
> > includes
> >
> 
> Let's be conservative. [[:blank:]] matches 2 characters, [[:space:]]
> matches Unicode ones that you want to add.
[...]

That's not true.

[[:blank:]] is horizontal spacing characters (like \h in perl),
[[:space:]] is all spacing characters (like \s in perl),
including vertical ones like \v, \f, \n...

On some systems (like the ones that follow ISO/IEC 30112 such as
GNU), that's excluding the ones that should not be considered as
delimiters (like U+00A0 the non-breaking space).

[[:blank:]], [[:space:]]... are POSIX character classes,
supported by most utilities that do wildcard or regexp matching.

I know of no other utility than zsh whose [[:space:]] includes
all the characters classified as "space" in the locale and where
[[:blank:]] doesn't include all the "blank" ones.

That struck me as very odd when I found that out yesterday and
is inconsistent with all other shells. But because that meant
extra code was added for that, I wondered if maybe that was
intentional.

It seems to me that if you wanted to match on only SPC and TAB
and not the other horizontal spacing characters classified as
such in the locale, you should use [ $'\t']. See also [[:IFS:]]
and [[:IFSSPACE:]] though they depend on the value of $IFS and
include \n by default (and \0 for [[:IFS:]]).

Now it's true that most people only care about SPC and TAB, and
since there's so much variation between systems as to what is
classified as "blank" (same for "alpha"... for that matters), it
probably doesn't matter that much. U+00A0 is probably the only
other horizontal spacing character that people are likely to
find in text that zsh is going to match [[:blank:]] against and
every other system doesn't consider it as "blank" (or "space"
for that matters).

-- 
Stephane