Re: 'case' pattern matching bug with bracket expressions

[Chet Ramey <chet.ramey@case.edu>]

On 5/14/15 10:42 AM, Peter Stephenson wrote:

> The handling of ']' at the start is mandated, if I've
> followed all the logic corretly --- POSIX 2007 Shell and Utilities
> 2.13.1 says:
> 
> [
>     If an open bracket introduces a bracket expression as in XBD RE
>     Bracket Expression, except that the <exclamation-mark> character (
>     '!' ) shall replace the <circumflex> character ( '^' ) in its role
>     in a non-matching list in the regular expression notation, it shall
>     introduce a pattern bracket expression. A bracket expression
>     starting with an unquoted <circumflex> character produces
>     unspecified results. Otherwise, '[' shall match the character
>     itself.
> 
> The languaqge is a little turgid, but I think it's saying "unless
> you have ^ or [ just go with the RE rules in [section 9.3.5]".

I think it means that improperly-formed pattern bracket expressions have
to be matched by a literal `[' followed by whatever the following
characters mean.

> I haven't read through the "case" doc so there may be some killer reason
> why that " | " has to be a case separator and not part of a
> square-bracketed expression.  But that would seem to imply some form of
> hierarchical parsing in which those characters couldn't occur within a
> pattern.

It's the grammar.  If you want `|' to be in a pattern you have to quote it.
Otherwise it's a metacharacter and a token delimiter (section 2.2).

The basic idea is that you tokenize case patterns as words and analyze them
as patterns after doing so.

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/