createFileAtomically

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Creates a file atomically

Creates a file atomically by first creating and writing to a temporary file which is then renamed.

Keywords
utilities, programming, IO
Usage
## S3 method for class 'default':
createFileAtomically(filename, path=NULL, FUN, ..., skip=FALSE, overwrite=FALSE, backup=TRUE, verbose=FALSE)
Arguments
filename
The filename of the file to create.
path
The path to the file.
FUN
A function that creates and writes to the pathname that is passed as the first argument. This pathname is guaranteed to be a non-existing temporary pathname.
...
Additional argumentes passed to pushTemporaryFile() and popTemporaryFile().
skip
If TRUE and a file with the same pathname already exists, nothing is done/written.
overwrite
If TRUE and a file with the same pathname already exists, the existing file is overwritten. This is also done atomically such that if the new file was not successfully created,
backup
If TRUE and a file with the same pathname already exists, then it is backed up while creating the new file. If the new file was not successfully created, the original file is restore
verbose
A logical or Verbose.
Value

  • Returns (invisibly) the pathname.

See Also

Internally, pushTemporaryFile() and popTemporaryFile() are used for working toward a temporary file, and pushBackupFile() and popBackupFile() are used for backing up and restoring already existing file.

Aliases
  • createFileAtomically.default
  • createFileAtomically
Examples
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Create a file atomically
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
n <- 10;
createFileAtomically("foobar.txt", FUN=function(pathname) {
  cat(file=pathname, "This file was created atomically.
");
  cat(file=pathname, "Timestamp: ", as.character(Sys.time()), "", sep="");
  for (kk in 1:n) {
    cat(file=pathname, kk, "", append=TRUE);
    Sys.sleep(0.1);
  }
  cat(file=pathname, "END OF FILE
", append=TRUE);
}, overwrite=TRUE)

bfr <- readLines("foobar.txt");
cat(bfr, sep="");


# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Overwrite the file atomically (emulate write failure)
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
tryCatch({
  createFileAtomically("foobar.txt", FUN=function(pathname) {
    cat(file=pathname, "Trying to create a new file.
");
    cat(file=pathname, "Writing a bit, but then an error...
", append=TRUE);
    # Emulate write error
    stop("An error occured while writing to the new file.");
    cat(file=pathname, "END OF FILE
", append=TRUE);
  }, overwrite=TRUE)
}, error = function(ex) {
  print(ex$message);
})

# The original file was never overwritten
bfr2 <- readLines("foobar.txt");
cat(bfr2, sep="");
stopifnot(identical(bfr2, bfr));

# The partially temporary file remains
stopifnot(isFile("foobar.txt.tmp"));
bfr3 <- readLines("foobar.txt.tmp");
cat(bfr3, sep="");

file.remove("foobar.txt.tmp");
Documentation reproduced from package R.utils, version 1.7.0, License: LGPL (>= 2.1)

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