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A general description is here.
‘R CMD Rprof|build|check’ are now based on R rather than Perl scripts. The only remaining Perl scripts are the rarely used ‘R CMD Sd2Rd’, ‘install-info.pl’ (used only if ‘install-info’ is not found) and some maintainer-mode-only scripts.
‘R CMD’ no longer manipulates the environment variables ‘PERL5LIB’ and ‘PERLLIB’.