Issue with Bash RegEx Handling

[Gerhard Jäger]

On 03.07.26 at 23:27 Keith Thompson wrote:
> I've reproduced the problem, and it appears to be a change in the
> newlib regular expression implementation, for a case that POSIX
> leaves undefined.
> 
> I have bash 5.3 built from source, which apparently is a bit more
> verbose than the default /usr/bin/bash.exe.
> 
> Here's a simpler example:
> 
> $ [[ x =~ ^(foo|)$ ]] ; echo $?
> bash: [[: invalid regular expression `^(foo|)$': empty (sub)expression
> 2
> $ [[ '' =~ ^(foo|)$ ]] ; echo $?
> bash: [[: invalid regular expression `^(foo|)$': empty (sub)expression
> 2
> $·
> 
> The expected result is 1 (no match) for the first and 0 (match) for
> the second.  A result of 2 indicates an invalid regular expression.
[...]

Thank you for sheding some light on this. It's unfortunate that such
expressions work on older versions, but undefined remains undefined :(

Regards,
  Gerhard

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