Rainer,
Download the R-devel build from http://mac.r-project.org 
The build is available under "Universal nightly builds for Mac OS X (10.6+ and 10.9+)" table.
R-devel-el-capitan-sa-x86_64.tar.gz (67Mb)
http://mac.r-project.org/el-capitan/R-devel/R-devel-el-capitan-sa-x86_64.tar.gz 
R-devel-el-capitan-signed.pkg (77Mb, installer incl. GUI)
http://mac.r-project.org/el-capitan/R-devel/R-devel-el-capitan-signed.pkg 
Best,
JJB
On 3/23/20, 9:06 AM, "R-SIG-Mac on behalf of Rainer M Krug" <r-sig-mac-bounces using r-project.org on behalf of Rainer using krugs.de> wrote:
    Hi
    
    I know - homebrew is not a supported installation approach to R, but I am asking anyway:
    
    Is there a way of installing r-devel via homebrew? Otherwise, what is the easiest way of getting r-devel on my Mac, without interfering with the homebrew install?
    
    Thanks,
    
    Rainer
    
    
    --
    Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany)
    
    Orcid ID: 0000-0002-7490-0066
    
    Department of Evolutionary Biology and Environmental Studies
    University of Zürich
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