Create Names for Temporary Files

Description

tempfile returns a vector of character strings which can be used as names for temporary files.

Usage

tempfile(pattern = "file", tmpdir = tempdir(), fileext = "")
tempdir(check = FALSE)

Arguments

Details

The length of the result is the maximum of the lengths of the three arguments; values of shorter arguments are recycled.

The names are very likely to be unique among calls to tempfile in an R session and across simultaneous R sessions (unless tmpdir is specified). The filenames are guaranteed not to be currently in use.

The file name is made by concatenating the path given by tmpdir, the pattern string, a random string in hex and a suffix of fileext.

By default, tmpdir will be the directory given by tempdir(). This will be a subdirectory of the per-session temporary directory found by the following rule when the R session is started. The environment variables TMPDIR, TMP and TEMP are checked in turn and the first found which points to a writable directory is used: if none succeeds ‘/tmp’ is used. The path must not contain spaces. Note that setting any of these environment variables in the R session has no effect on tempdir(): the per-session temporary directory is created before the interpreter is started.

Value

For tempfile a character vector giving the names of possible (temporary) files. Note that no files are generated by tempfile.

For tempdir, the path of the per-session temporary directory.

On Windows, both will use a backslash as the path separator.

On a Unix-alike, the value will be an absolute path (unless tmpdir is set to a relative path), but it need not be canonical (see normalizePath) and on macOS it often is not.

Note on parallel use

R processes forked by functions such as mclapply and makeForkCluster in package parallel share a per-session temporary directory. Further, the ‘guaranteed not to be currently in use’ applies only at the time of asking, and two children could ask simultaneously. This is circumvented by ensuring that tempfile calls in different children try different names.

Source

The final component of tempdir() is created by the POSIX system call mkdtemp, or if this is not available (e.g. on Windows) a version derived from the source code of GNU glibc.

It will be of the form ‘RtmpXXXXXX’ where the last 6 characters are replaced in a platform-specific way. POSIX only requires that the replacements be ASCII, which allows . (so the value may appear to have a file extension) and regexp metacharacters such as +. Most commonly the replacements are from the regexp pattern [A-Za-z0-9], but . has been seen.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

unlink for deleting files.

Examples

tempfile(c("ab", "a b c"))   # give file name with spaces in!

tempfile("plot", fileext = c(".ps", ".pdf"))

tempdir() # works on all platforms with a platform-dependent result


## Show how 'check' is working on some platforms:
if(exists("I'm brave") && `I'm brave` &&
   identical(.Platform$OS.type, "unix") && grepl("^/tmp/", tempdir())) {
  cat("Current tempdir(): ", tempdir(), "\n")
  cat("Removing it :", file.remove(tempdir()),
      "; dir.exists(tempdir()):", dir.exists(tempdir()), "\n")
  cat("and now  tempdir(check = TRUE) :", tempdir(check = TRUE),"\n")
}