It's all documented in ?regexp.  "." is a regex metacharacter.
Metacharacters have to be escaped via "\\".

In particular, note:

"The fundamental building blocks are the regular expressions that match a
single character. Most characters, including all letters and digits, are
regular expressions that match themselves. Any metacharacter with special
meaning may be quoted by preceding it with a backslash. The metacharacters
in EREs are . \ | ( ) [ { ^ $ * + ?, but note that whether these have a
special meaning depends on the context. "

and

"Patterns are described here as they would be printed by cat: (*do remember
that backslashes need to be doubled when entering R character strings*,
e.g. from the keyboard). "

So presumably

files <- files[grep("^\\.*$", files)]

is what you want.

-- Bert




On Sun, Jul 8, 2012 at 5:47 AM, syrvn <mentor_@gmx.net> wrote:

> Hello,
>
> when I use list.files with recursive = TRUE and all.files = TRUE, R returns
> a list of strings/paths.
> >From all those strings I want to keep only the ones starting with a .
> I tried using grep to achieve that. However, the problem is that because of
> the recursive list.files parameter,
> for some files beginning with a . there is a path attached. I think it is
> not as simple as it looks because all files
> end with . something. .xlsx or .txt or .r...
>
> files <- list.files("~", recursive = TRUE, all.files = TRUE)
> files
> /XXX/ZZZ/.R_history
> /XXX/ZZZ/AAA/Script.r
> /XXX/ZZZ/BBB/test.xlsx
> /XXX/ZZZ/CCC/.xyz
>
> files <- files[grep("^.*$", files)]
>
> I want grep to return only the following to lines:
>
> /XXX/ZZZ/.R_history
> /XXX/ZZZ/CCC/.xyz
>
> Any ideas on how to solve that issue?
>
> Cheers
> syrvn
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/list-files-find-files-beginning-with-a-tp4635773.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

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