[your code here]

[qjnr]

/* This is a very basic implementation of cat in the D 
programming language.
    For more info about the D programming language, visit 
https://dlang.org .

    Copyright (c) 2018 qjnr */

import std.stdio : readln, write, writef;
import std.file : readText, exists;

void main(string[] args)
{
   if (args.length is 2)
   {
     string fname = args[1];
     if (!exists(fname))
     {
       writef("cat: %s: No such file or directory", fname);
     }
     else
     {
       string content = readText(fname);
       write(content);
     }
   }
   else
   {
     string line;
     while ((line = readln()) !is null)
     {
       write(line);
     }
   }
}