How to resolve the algorithm Append a record to the end of a text file step by step in the Elixir programming language

Published on 12 May 2024 09:40 PM
#Elixir

How to resolve the algorithm Append a record to the end of a text file step by step in the Elixir programming language

Table of Contents

Problem Statement

Many systems offer the ability to open a file for writing, such that any data written will be appended to the end of the file. Further, the file operations will always adjust the position pointer to guarantee the end of the file, even in a multitasking environment. This feature is most useful in the case of log files, where many jobs may be appending to the log file at the same time, or where care must be taken to avoid concurrently overwriting the same record from another job.

Given a two record sample for a mythical "passwd" file: Resulting file format: should mimic Linux's /etc/passwd file format with particular attention to the "," separator used in the GECOS field. But if the specific language has a particular or unique format of storing records in text file, then this format should be named and demonstrated with an additional example. Expected output: Finally: Provide a summary of the language's "append record" capabilities in a table. eg. Alternatively: If the language's appends can not guarantee its writes will always append, then note this restriction in the table. If possible, provide an actual code example (possibly using file/record locking) to guarantee correct concurrent appends.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Append a record to the end of a text file step by step in the Elixir programming language

Source code in the elixir programming language

defmodule Gecos do
  defstruct [:fullname, :office, :extension, :homephone, :email]
  
  defimpl String.Chars do
    def to_string(gecos) do
      [:fullname, :office, :extension, :homephone, :email]
      |> Enum.map_join(",", &Map.get(gecos, &1))
    end
  end
end
 
defmodule Passwd do
  defstruct [:account, :password, :uid, :gid, :gecos, :directory, :shell]
  
  defimpl String.Chars do
    def to_string(passwd) do
      [:account, :password, :uid, :gid, :gecos, :directory, :shell]
      |> Enum.map_join(":", &Map.get(passwd, &1))
    end
  end
end

defmodule Appender do
  def write(filename) do
    jsmith = %Passwd{
      account: "jsmith",
      password: "x",
      uid: 1001,
      gid: 1000,
      gecos: %Gecos{
        fullname: "Joe Smith",
        office: "Room 1007",
        extension: "(234)555-8917",
        homephone: "(234)555-0077",
        email: "jsmith@rosettacode.org"
      },
      directory: "/home/jsmith",
      shell: "/bin/bash"
    }
    
    jdoe = %Passwd{
      account: "jdoe",
      password: "x",
      uid: 1002,
      gid: 1000,
      gecos: %Gecos{
        fullname: "Jane Doe",
        office: "Room 1004",
        extension: "(234)555-8914",
        homephone: "(234)555-0044",
        email: "jdoe@rosettacode.org"
      },
      directory: "/home/jdoe",
      shell: "/bin/bash"
    }
    
    xyz = %Passwd{
      account: "xyz",
      password: "x",
      uid: 1003,
      gid: 1000,
      gecos: %Gecos{
        fullname: "X Yz",
        office: "Room 1003",
        extension: "(234)555-8913",
        homephone: "(234)555-0033",
        email: "xyz@rosettacode.org"
      },
      directory: "/home/xyz",
      shell: "/bin/bash"
    }
    
    File.open!(filename, [:write], fn file ->
      IO.puts(file, jsmith)
      IO.puts(file, jdoe)
    end)
    
    File.open!(filename, [:append], fn file ->
      IO.puts(file, xyz)
    end)
    
    IO.puts File.read!(filename)
  end
end

Appender.write("passwd.txt")

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