Re: Handling of escaped plus sign ("+") in regular expressions

[Eric Cook <llua@gmx.com>]

On 5/20/20 3:18 PM, Marco Trevisan wrote:
> Hi,
>
> I've been using zsh to run some local scripts I was normally running with
> bash and while most of them work as expected, there's a case that weirdly
> failed to me (using zsh 5.8):
>
> [[ +123 =~ ^+[0-9]+$ ]]
> zsh: failed to compile regex: Invalid preceding regular expression
>
> [[ +123 =~ ^\+[0-9]+$ ]]
> zsh: failed to compile regex: Invalid preceding regular expression
>
> The same behavior seems to apply both using RE_MATCH_PCRE and not.
> As said, both matches correctly using bash.
>
> Using something like
>
> [[ +123 =~ ^[+][0-9]+$ ]]
>
> Works as expected instead.
>

bash's [[ =~ uses regex from the libc it was compiled against last time i checked.
and with libc's for the systems i have available, that won't work. it doesn't spit
out an error message like zsh does, but it correctly does not match the invalid regex.