regexp [. .]

Parker Anderson baka.rob at
Wed Jan 17 02:42:05 UTC 2007

On 1/16/07, applecom at <applecom at> wrote:
> I need to use regular expressions with a sequence of characters as a
> collating element.
>  From re_format(7):
> "Within a bracket expression, a collating element (a character, a multi-
> character sequence that collates as if it were a single character, or a
> collating-sequence name for either) enclosed in `[.' and `.]' stands for
> the sequence of characters of that collating element.  The sequence is a
> single element of the bracket expression's list.  A bracket expression
> containing a multi-character collating element can thus match more than
> one character, e.g. if the collating sequence includes a `ch' collating
> element, then the RE `[[.ch.]]*c' matches the first five characters of
> `chchcc'."
> But grep (and other programs using regexp) writes on "echo somepattern |
> grep -Ee 'some[^[.pattern.]]'":
> "Invalid collation character". What's wrong?

After some searching around I found the following post (albeit for a
different project):

An excerpt:

I have to admit to having no experience with collating characters.
That said, I'll convey my understanding of them.

You cannot use [. and .] to group an arbitrary pair of characters
together.  Collating characters are defined by the locale in which
you're running, and only those defined by the locale are available for
use inside [. and .].  They usually have names, defined by the
locale; the name may or may not be the actual sequence of characters,
such [as] '[.ch.].'

I'm not sure, myself, but I hope that helps and isn't far from the
truth ;)  If anyone knows otherwise, please let me know.

Is there a certain match you are trying to pattern?  From the looks of
it, [ch]* would match a similar set of characters, but it isn't as
strict about which pattern they should be in.


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