How to prevent from overwriting the file? - r

Question

I'm looking for a way to prevent R from overwriting files during the session. The more general solution then better.
Currently I got bunch of functions called e.g.: safe.save, safe.png, safe.write.table which are implemented more or less as
safe.smth <- function(..., file) {
if (file.exists(file))
stop("File exists!")
else
smth(..., file=file)
}
It works, but only if I got control over execution. If some (not mine) function created file I can't stop it from overwrite.
Another way is to set read only flag on files, which also top R from overwriting existing files. But this has drawbacks as well (e.g.: you don't know which files needs to be protected).
Or write one-liner:
protect <- function(p) if (file.exists(p)) stop("File exsits!") else p
and use it always when providing filename.
Is there a way to force this behaviour session wide? Some kind of global setting for connections? Maybe only for subset of functions (graphics devices, file-created connections, etc)? Maybe some system specific solution?
The following could be used as test case:
test <- function(i) {
try(write.table(i, "test_001.csv"))
try(writeLines(as.character(i), "test_002.txt"))
try({png("test_003.png");plot(i);dev.off()})
try({pdf("test_004.pdf");plot(i);dev.off()})
try(save(i, file="test_005.RData"))
try({f<-file("test_006.txt", "w");cat(as.character(i), file=f);close(f)})
}
test(1)
magic_incantations() # or magic_incantations(test(2)), etc.
test(2) # should fail on all writes (to test set read-only to files from first call)

Answer 1

The conventional way to avoid clobbering data files isn't to look for OS hacks, but to use filenames and directories that are special for your session.
session.dir <- tempdir()
...
write.table(i, file.path(session.dir,"test_001.csv"))
writeLines(as.character(i), file.path(session.dir,"test_002.txt"))
...
or
session.pid <- Sys.getpid()
...
write.table(i, paste0("test_001.",session.pid,".csv"))
writeLines(as.character(i), paste0("test_002.",session.pid,".txt"))
...