R Text Files and Connections

How it works

Connections represent input or output streams. Opening and closing them deliberately prevents leaked handles and incomplete writes. This example writes a tiny UTF-8 text fixture through a file connection, closes it before reading and registers a cleanup fallback. Network and compressed connections have additional failure boundaries not implied by a local text read.

Run this R example

These examples run locally with R, not PHP, Python or JavaScript. The reviewed baseline is R 4.5.2 on Windows x64/UCRT, using only packages shipped with R. This is a tested version, not a newest-release claim. Install your own R from the official R project; an IDE is optional. Save the complete source as text-connections.R in a separate learning folder and run Rscript --vanilla text-connections.R. Keep code and fictional fixtures separate from a real project.

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The complete download uses a local scope, restores its temporary options and treats unexpected warnings as errors. Examples that handle an expected warning do so narrowly. Random examples change only their R process’s RNG state. File examples own their temporary output; figure examples leave their named PNG in the current learning folder and refuse to overwrite it. Use a new empty folder to rerun a figure.

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Example

local({
  previous_options <- options(warn = 2, digits = 8, stringsAsFactors = FALSE)
  on.exit(options(previous_options), add = TRUE)
  path <- tempfile("bhylu-note-", fileext = ".txt")
  if (file.exists(path)) stop("Refuse an existing file")
  on.exit(if (file.exists(path)) unlink(path), add = TRUE)
  connection <- file(path, open = "wt", encoding = "UTF-8")
  on.exit(if (!is.null(connection)) close(connection), add = TRUE, after = FALSE)
  writeLines(c("East room", "Three sessions"), connection)
  close(connection)
  connection <- NULL
  lines <- readLines(path, encoding = "UTF-8", warn = FALSE)
  cat("lines:", length(lines), "\n")
  cat(paste(lines, collapse = " | "), "\n")
  invisible(NULL)
})

path <- tempfile("bhylu-note-", fileext = ".txt")
if (file.exists(path)) stop("Refuse an existing file")
on.exit(if (file.exists(path)) unlink(path), add = TRUE)
connection <- file(path, open = "wt", encoding = "UTF-8")
on.exit(if (!is.null(connection)) close(connection), add = TRUE, after = FALSE)
writeLines(c("East room", "Three sessions"), connection)
close(connection)
connection <- NULL
lines <- readLines(path, encoding = "UTF-8", warn = FALSE)
cat("lines:", length(lines), "\n")
cat(paste(lines, collapse = " | "), "\n")

Expected result

lines: 2
East room | Three sessions

The fallback close is placed before file removal in exit order. On success, setting the connection variable to NULL prevents closing an already-closed handle again. Reading known complete lines is not a general parser for arbitrary data.