[R-pkg-devel] perl = TRUE fails on ubuntu

[Kevin Ushey]

Hi Josiah,

Why not share a reprex / something we can copy and paste to directly
reproduce the issue?

In any case, I suspect this depends on the underlying PCRE
implementation, and so isn't really directly an R issue. You might
have luck if you rewrite your regular expression from:

    (?<=(FeatureServer|MapServer)/)[0-9]+/?$

to something like (I didn't count parentheses below so assume I made a mistake)

    (?:(?<=FeatureServer)|(?<=MapServer)))/)[0-9]+/?$

Or, alternatively -- does this really need to be a lookbehind? Can you
just match that text as-is and then capture whatever you happen to
find in front of it?

Best,
Kevin

On Tue, May 27, 2025 at 3:07 PM Josiah Parry <josiah.parry using gmail.com> wrote:
>
> Hi all,
>
> I've encountered an issue where using `perl = TRUE` for regular expressions
> with grepl() causes an error on ubuntu CI runners only.
>
> Is this a known limitation of perl = TRUE for grep and family in base R? Or
> is there a suggested workaround?
>
> The issue is specifically with lookbehinds:
>
> PCRE pattern compilation error
> 'lookbehind assertion is not fixed length'
> at '(?<=(FeatureServer|MapServer)/)[0-9]+/?$'
>
> Any guidance would be very much appreciated! I'd like to avoid adding a
> stringi dependency if possible.
>
>         [[alternative HTML version deleted]]
>
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