Filesystem

Introduction

This introduction to working with the filesystem is grossly simplified. It does, however, cover enough to get started with most projects.

Exploring the Filesystem

Our current working directory (in two different forms of error handling):

{:ok, cwd} = File.cwd()

{
  cwd,
  File.cwd!()
}

What is in that directory?

files =
  [cwd, "*"]
  |> Path.join()
  |> Path.wildcard()

Which of these are directories?

dirs =
  files
  |> Enum.filter(&File.dir?/1)

Preliminaries

First, lets come up with a filename that is highly unlikely to hurt anyone:

filename = "30c39b99-b9a8-4789-91ad-6283e43d1433"

Lets verify that it does not exist:

File.exists?(filename)

Note: Only continue if this returns false.

Writing to Files

{:ok, writer} = File.open(filename, [:write])
IO.write(writer, "Hello")
File.close(writer)

Appending to Files

{:ok, appender} = File.open(filename, [:append])
IO.write(appender, ", World")
File.close(appender)

Reading from Files

Reading of entire file:

case File.read(filename) do
  {:ok, lines} ->
    IO.puts(lines)

  {:error, details} ->
    IO.puts("Unable to read #{filename}: #{details}")
end

If the file is large, that is likely to be a bad idea. Instead the IO.read/2 function offers more control. In this case we read the first couple of characters (but there is also an option for reading a line):

{:ok, reader} = File.open(filenameThis)

reader
|> IO.read(5)
|> IO.puts()

File.close(reader)

Removing Files

Finally, lets clean up after ourselves:

File.rm(filename)