| CRAN | R Documentation | 
This function allows package developers to run tests 
themselves that should not run on CRAN or with 
"R CMD check --as-cran" because of compute 
time constraints with CRAN tests.
CRAN(CRAN_pattern, n_R_CHECK4CRAN)
CRAN_pattern | 
 a regular expressions to apply to the names of 
  | 
n_R_CHECK4CRAN | 
 Assume this is   | 
The "Writing R Extensions" manual says that 
"R CMD check" can be customized 
"by setting environment variables 
_R_CHECK_*_:, as described in" the 
Tools section of the "R Internals" manual.
'R CMD check' was tested with 
R 3.0.1 under Fedora 18 Linux and with
Rtools 3.0 from April 16, 2013 under 
Windows 7.  With the '--as-cran'
option, 7 matches were found;  without it, 
only 3 were found.  These numbers were 
unaffected by the presence or absence of the 
'–timings' parameter.  On this basis, the 
default value of n_R_CHECK4CRAN was 
set at 5.
1.  x. <- Sys.getenv()
2.  Fix CRAN_pattern and 
n_R_CHECK4CRAN if missing.
3.  Let i be the indices of 
x. whose names match all the patterns 
in the vector x.
4.  Assume this is CRAN if 
length(i) >= n_R_CHECK4CRAN.
a logical scalar with attributes 
'Sys.getenv' containing the 
results of Sys.getenv() and 
'matches' containing i per step 
3 above.
Spencer Graves (copied from the 
fda package)
Sys.getenv
skip_on_cran, which uses 
["the NOT_CRAN env var set by devtools and friends"](https://testthat.r-lib.org/reference/skip.html).  This 
CRAN function does NOT require a user to 
set any environment variable. 
cran <- CRAN()
str(cran)
gete <- attr(cran, 'Sys.getenv')
(ngete <- names(gete))
iget <- grep('^_', names(gete))
gete[iget]
#\dontrun is sometimes run on CRAN.  See
#https://github.com/ThinkR-open/prepare-for-cran
#accessed 2021-06-14
if (interactive()) {
if(CRAN()){
  stop('CRAN')
} else {
  stop('NOT CRAN')
}
}
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