createFileAtomically

From R.utils v1.28.4 by Henrik Bengtsson

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, th
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 restored
verbose: A logical or Verbose.

Value

Returns (invisibly) the pathname.

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)
    # Emulate a slow process
    if (interactive()) 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 1.28.4, License: LGPL (>= 2.1)

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