Re: built-in regex matches wrong character

[Eric Blake]

On 09/05/2018 01:50 PM, mamatb@mamatb-laptop wrote:

> Description:
>         It seems like bash built-in regex matches some symbols that shouldn't. 
> The following commands shows this:
>                 [[ 'º' =~ [o-p] ]] && [[ ! 'º' =~ o ]] && [[ ! 'º' =~ p ]] && 
> echo 'º between o and p but none of them'
>                 [[ 'ª' =~ [a-b] ]] && [[ ! 'ª' =~ a ]] && [[ ! 'ª' =~ b ]] && 
> echo 'ª between a and b but none of them'
>
> Repeat-By:
>         Actually found out this while developing a bigger bash script, but it 
> can be reproduced with the previous lines. Would you reply me at 
> amatbaeza@gmail.com to know if this was in fact a bug? Thanks.

Not a bug, but a property of your locale.

POSIX says that range expressions in regular expressions are 
implementation-defined except for in the C locale, which means [a-b] is 
free to match more than just the two ASCII characters 'a' and 'b', but 
rather anything that your current locale considers equivalent.

If you run your script with LC_ALL=C in the environment, you won't have 
that problem (because there, [a-b] is well-defined to be exactly two 
characters).  Or, you can use bash's 'shopt -s globasciiranges' which is 
supposed to enable Rational Range Interpretation, where even in non-C 
locales, a character range bounded by two ASCII characters takes on the 
C locale definition of only the ASCII characters in that range, rather 
than the locale's definition of whatever other characters might also be 
equivalent (actually, while I know that shopt affects globbing, I don't 
know if it also affects regex matching - but if it doesn't, that's 
probably a bug that should be fixed).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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