Re: [R] Parsing regular expressions differently - feature request

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Sat, 08 Nov 2008 08:51:08 -0500

Some feature to simplify entry of backslashes has been mentioned many times and keeps coming up from time to time. It would not only be useful for regexp's but also for latex and Windows path names and I too hope that it will be addressed.

On Sat, Nov 8, 2008 at 7:20 AM, John Wiedenhoeft <john_at_nurfuerspam.de> wrote:
> Hi there,
>
> I rejoiced when I realized that you can use Perl regex from within R. However,
> as the FAQ states "Some functions, particularly those involving regular
> expression matching, themselves use metacharacters, which may need to be
> escaped by the backslash mechanism. In those cases you may need a quadruple
> backslash to represent a single literal one. "
>
> I was wondering if that is really necessary for perl=TRUE? wouldn't it be
> possible to parse a string differently in a regex context, e.g. automatically
> insert \\ for each \ , such that you can use the perl syntax directly? For
> example, if you want to input a newline as a character, you would use \n
> anyway. At the moment one says \\n to make it clear to R that you mean \n to
> make clear that you mean newline... this is pretty annoying. How likely is it
> that you want to pass a real newline character to PCRE directly?
>
> If it's anyhow possible to pass everything between " and " directly to PCRE
> without expanding it internally in R, please add this to a future version (as
> an option like noescape=TRUE perhaps?)! I would love to use R instead of Perl
> for working with regex, without having to do two levels of escape all the
> time.
>
> Thanks,
> John
>
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