read-file.c

#include <stdio.h>
#include <unistd.h>
#define CHUNK 4096

int main()
{
  int     fd;
  char    buf[CHUNK];
  size_t  nRead;

  fd = open("test.txt", O_READ);
  
  // Reads then writes the data
  while(nRead = read(fd, CHUNK, buf))
    write(1, CHUNK, buf);

  close(fd);
}

open(1), read(1), write(1)