Re: fnmatch bug? escaping of '-' and ']' inside [...] does not work.

[Szabolcs Nagy <nsz@port70.net>]

* Denys Vlasenko <vda.linux@googlemail.com> [2017-08-15 15:12:17 +0200]:
> Moving bbox build to musl did uncover one definite bug.
> bbox has gazillion tests for its shells, and one of them
> started failing. I added debug printout and with it,
> the following fnmatch calls give different results now:
> 
> ash: fnmatch(pattern:'[a\-c]',str:'-',0):1
> ash: fnmatch(pattern:'[\]]',str:']',0):1
> ash: fnmatch(pattern:'[a\]]',str:']',0):1
> 
> glibc and uclibc threat the above as a match.
> 
> The assumption may be that one should place ']' or '-'
> as a first character in the [...] and thus escaping
> is not necessary, but shell does not have the luxury
> of choosing the pattern, in comes from the script.
> 

it's not clear to me if \ is valid as escape in fnmatch pattern:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_13_01

in re bracket expression \ is not an escape char,
but in the shell i think the pattern should be
unquoted first, which may or may not apply to
fnmatch bracket expression, depending on how you
read the text.

i guess if other implementations do the unquoting
musl should follow that, but the standard could
be improved.