cat cp.c
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#define N 1024

int main(int argc, char* argv[]) {
  char buf[N];
  int sf, df, size;

  if ((sf = open(argv[1], O_RDONLY)) == -1) {
    perror(argv[1]);
    exit(1);
  }
  if ((df = open(argv[2], O_WRONLY|O_CREAT|O_TRUNC, 0755)) == -1) {
    perror(argv[2]);
    close(sf);
    exit(2);
  }
  while((size = read(sf, buf, N)) > 0) {
    write(df, buf, size);
  }
  close(df);
  close(sf);

  return 0;
}


cat cmp.c
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<stdio.h>

#define N 1024

int main(int argc, char *argv[]) {
 int fd1, fd2;
 char buf1[N], buf2[N];
 int n1, n2, i;

 if ((fd1 = open(argv[1], O_RDONLY)) == -1) {
  perror(argv[1]);
  return 2;
 }
 if ((fd2 = open(argv[2], O_RDONLY)) == -1) {
  perror(argv[2]);
  return 3;
 }

 while((n1 = read(fd1, buf1, N)) > 0 && (n2 = read(fd2, buf2, N)) > 0) {
  if (n1 != n2) {
   return 1;
  }
  for (i = 0; i < n1; i++) {
   if (buf1[i] != buf2[i]) {
    return 1;
   }
  }
 }

 return 0;

 close(fd2);
 close(fd1);

 return 0;
}