R Under development (unstable) (2024-06-25 r86831 ucrt) -- "Unsuffered Consequences"
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> library("foreign")
> (dd <- data.frame(name  = c("apple", "banana", "carrot", NA),
+                   gender= c("male", "female", "male", "female"), stringsAsFactors = FALSE))
    name gender
1  apple   male
2 banana female
3 carrot   male
4   <NA> female
> ##   name gender
> ## 1    a   male
> ## 2    b female
> ## 3    c   male
> ## 4 <NA> female
> setwd(tempdir())
> tfSi <- "temp_for_sas_import.txt"
> ti   <- "temp_import.sas"
> write.foreign(dd, datafile = tfSi, codefile = ti, package = "SAS")
> file.show(tfSi) # the NA is shown as <empty>
> writeLines(sasCodes <- readLines(ti))
* Written by R;
*  write.foreign(dd, datafile = tfSi, codefile = ti, package = "SAS") ;

DATA  rdata ;
LENGTH
 name $ 6
 gender $ 6
;

INFILE  "temp_for_sas_import.txt" 
     DSD 
     LRECL= 21 ;
INPUT
 name
 gender $ 
;
RUN;
> ## This failed in foreign <= 0.8-71 :
> stopifnot(identical(" name $ 6",
+                     grep(" name ", sasCodes, value=TRUE)))
> 
> ## This site was unresponsive in Jan 2014
> if(!nzchar(Sys.getenv("R_FOREIGN_FULL_TEST"))) q("no")
> proc.time()
   user  system elapsed 
   0.31    0.04    0.31